Spread vs square bore manifolds and carbs
Dre
manifold??
I'd like to pull the (buggered) quad off a 308 with spreadbore manifold and
stick a squarebore holley on it, is this possible??
Cheers Dre
a9x5l
Unless you're using a manifold like the Edelbrock Performer, you need to
use an adaptor plate. Don't forget to check for bonnet clearance after the
swap ;-)
--
a9x5l
Noddy
"Dre" <ausjul...@hotmail.com> wrote in message
news:4532f0f5$1...@patrick.nettas.net...
> I'd like to pull the (buggered) quad off a 308 with spreadbore manifold
> and stick a squarebore holley on it, is this possible??
You need an adapter.
--
Regards,
Noddy.
Dre
news:4532fe15$1...@news.comindico.com.au...
Damn, see my other post :(
No clearance...
Cheers Dre
Dre
news:pan.2006.10.16....@hotmail.com...
Shit, bonnet clearance was my next question.
Time to find a spreadbore me thinks...
Cheers Dre
Noddy
> Damn, see my other post :(
>
> No clearance...
There are adapters around that are only 5/8 inch thick.
--
Regards,
Noddy.
Dre
Easier just to get a spreadbore me thinks, since I dont have a pref and I
dont have one yet :)
Or do squarebores shit on spreadbores?
Cheers Dre
a9x5l
Just get a 650 Holley with vacuum secondaries, they work great on a 308
and no need for an adaptor.
--
a9x5l
a9x5l
As I've said in another post, a 650 Holley with vacuum secondaries will be
a good replacement for the Quaddy.
--
a9x5l
matt vk3zmw
better option: bolt-on Holley or Edelbrock throttle-body injection.
BTW, how do you know the quaddy is buggered?
Noddy
> Or do squarebores shit on spreadbores?
Squarebores are generally the hot performance ticket, but spreadbores make
excellent noises when the secondaries open :)
--
Regards,
Noddy.
Noddy
> As I've said in another post, a 650 Holley with vacuum secondaries will be
> a good replacement for the Quaddy.
Agreed.
--
Regards,
Noddy.
Noddy
"matt vk3zmw" <nos...@nospam.ever> wrote in message
news:F3IYg.48107$rP1....@news-server.bigpond.net.au...
> better option: bolt-on Holley or Edelbrock throttle-body injection.
Only just.
Throttle body injectors are pretty average at best, and if I was going to
that trouble it wouldn't be much more difficult to go fabricated
multi-point.
> BTW, how do you know the quaddy is buggered?
It's a Quaddy :)
--
Regards,
Noddy.
Toby Ponsenby
Yeah, right - now the fuel price is on the way down for the (Yankee
elections).
But after that... methinks mechanical secondary carbs will regain
their popularity as seen post 70's oil crisis:-)
Dre
What about a 600 vac secondary??
Cheers Dre
Dre
Noted. How would a sqaurebore 600 with vac secondaries compare to this??
Cheers Dre
Dre
Cheers Dre
Dre
news:F3IYg.48107$rP1....@news-server.bigpond.net.au...
>> Hi all, I should know this, but does a square bore carb fit a spread bore
>> manifold??
>>
>> I'd like to pull the (buggered) quad off a 308 with spreadbore manifold
>> and stick a squarebore holley on it, is this possible??
>>
>> Cheers Dre
> Cheap option: Edelbrock spreadbore carby w/ vac secondaries.
problem is they are even harder for me to find than the spreadbore holleys!
> better option: bolt-on Holley or Edelbrock throttle-body injection.
>
> BTW, how do you know the quaddy is buggered?
I've spend ages on it and too much money, I cant find anyone that really
knows them and its still running like a piece of shit so its going. Too
inconisitant. I've tried, failed so going back to what works (or what I can
make work anyway)
Cheers Dre
Noddy
"Athol" <m...@privacy.net> wrote in message
news:11610386...@idlwebserver.idl.com.au...
> Just to keep John McK happy, I haven't mentioned the brand of mixer. :-)
:)
--
Regards,
Noddy.
Dre
>
>> Just get a 650 Holley with vacuum secondaries, they work great on a 308
>> and no need for an adaptor.
>
> on top of the rochester throttlebody. Overall height is about the same as
> the rochester except that the mixer is higher inside the air filter.
>
> Just to keep John McK happy, I haven't mentioned the brand of mixer. :-)
>
> Athol
> <http://cust.idl.com.au/athol> Linux Registered User # 254000
> I'm a Libran Engineer. I don't argue, I discuss.
I'd love to, but I'm trying to keep the cost down as much as I can.
All I need atm is a carb.
Would a 600 squarebore vac secondary be ok for a mild 308?? (previously had
a quad)
Cheers Dre
Dan---
news:11610386...@idlwebserver.idl.com.au...
> a9x5l <a9...@hotmail.com> wrote:
>
> Just to keep John McK happy, I haven't mentioned the brand of mixer. :-)
Why would you want to keep John happy ?. ;-)
--
Regards
Dan
Noddy
> Would a 600 squarebore vac secondary be ok for a mild 308?? (previously
> had a quad)
It'd work, but like anything how well it works will depend entirely on your
ability to get it sorted. Simply plonking it on and expecting it to be
"right" straight off the bat will leave you disappointed.
--
Regards,
Noddy.
Dre
I was more referring to a comparison between a 600 square vs 650 spread
(both vac secondaries), is one HEAPS better??
If there isn't much of a difference I'll go with a 600 (I can get a reco 600
square for the same price as a used 650 spread).
Cheers Dre
eeviil inc.
running a 308 with a spreadbore 650 (I think it's a 650) vac secondary
carb, the car goes great, and the carby has never given me any grief.
For all the extra stuffing around it's probably worth going and getting
a reco spreadbore, rather than dealing with bonnet clearance, etc, all
for a few extra HP if any. As it is in my commodore, my 9x2" K&N filter
touches the bonnet, but then again I think my manifold sits a bit higher
than standard holden manifolds.
Adam
eeviil inc.
They aren't THAT bad a carby. Maybe you just don't know how to tune them
properly :P
I know I sure as hell can't :)
Adam
eeviil inc.
Hahahaha yep it's a quaddy alright. When somebody that can tune them
does it right they are a brilliant carby, until they are tuned correctly
they can be a total PITA, which is generally about 90% of the time...
Adam
Dre
news:453438a8$0$11968$afc3...@news.optusnet.com.au...
Yeah I'm pretty much convinced now to go with a spread, plus there is less
chance of an air leak with only one gasket vs 2.
The next potential problem is I have one of those lower air filter housings,
the ones that fit 3" high air filters. Does anyone know if that will fit
over that moulded bit sticking out of the middle of the carb? Hard to
describe, but the hole for the bolt for the air cleaner is lower than the
highest point of the carb. Will that point (highest), clear the under side
of the top bit of the air filter housing??
Cheers Dre
Dre
Yep, totally agree, and I've been fiddling with it for ages (waaaay to long
:)
To cut a long story short, I'm planning to stick an efi manifold from a VS
commodore on the engine (the engine allready has VS heads, cam and exhaust)
soon (ish), but in the meantime I need it to run better, so chuck a holley
on it, tune it, drive it, then use the holley on a 308 in my Torana when the
engine is finished and the efi is fitted. Yes, a lot of stuffing around,
but hey, thats part of the fun :)
Cheers Dre
Noddy
> I was more referring to a comparison between a 600 square vs 650 spread
> (both vac secondaries), is one HEAPS better??
There's a noticeable difference, but I wouldn't say it's huge, and you'd
have to have the rest of your shit well sorted before you could pick any
real significant benefits.
If you can get a new (or rebuilt) 600 cheap enough, then that won't
disappoint you.
--
Regards,
Noddy.
Noddy
> They aren't THAT bad a carby. Maybe you just don't know how to tune them
> properly :P
No one can. Their fuel metering system has got bigger tits than my missus :)
--
Regards,
Noddy.
Dre
Cheers Dre
John McKenzie
The quick answer is yes. But you'd need to deal with the different bolt
pattern. You'll need an adapter plate to fit it.
--
John McKenzie
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Dre
news:453459...@alphalink.com.au...
> Dre wrote:
>>
>> "Athol" <m...@privacy.net> wrote in message
>> news:11610386...@idlwebserver.idl.com.au...
>> > a9x5l <a9...@hotmail.com> wrote:
>> >
>> >> Just get a 650 Holley with vacuum secondaries, they work great on a
>> >> 308
>> >> and no need for an adaptor.
>> >
>> > Of course, the option that I personally prefer is to chuck an LPG mixer
>> > on top of the rochester throttlebody. Overall height is about the same
>> > as
>> > the rochester except that the mixer is higher inside the air filter.
>> >
>> > Just to keep John McK happy, I haven't mentioned the brand of mixer.
>> > :-)
>> >
>> > --
>> > Athol
>> > <http://cust.idl.com.au/athol> Linux Registered User # 254000
>> > I'm a Libran Engineer. I don't argue, I discuss.
>>
>> I'd love to, but I'm trying to keep the cost down as much as I can.
>>
>> All I need atm is a carb.
>>
>> Would a 600 squarebore vac secondary be ok for a mild 308?? (previously
>> had
>> a quad)
>
> The quick answer is yes. But you'd need to deal with the different bolt
> pattern. You'll need an adapter plate to fit it.
>
it'll be a bit harder to find, but I'm in no huge rush.
Am I right in saying that the throttle body on a spreadbore is similar in
operation to a Quad re the secondaries?? But a square bore, all 4
butterflies open at the same time?
Cheers Dre
a9x5l
If you use a 14" low profile air cleaner housing(one with clearance for
the float bowls) it should fit, but, don't use a filter less than 3" tall
as there won't be enough room around the choke housing and the air flow
into the engine will be very restricted(believe me, I've tried it!).
Something like this...
http://www.moroso.com/catalog/categorydisplay.asp?catcode=34003
--
a9x5l
a9x5l
There won't be much in it performance wise though the spreadbore should
have slightly better part-throttle responsiveness and overall fuel economy.
--
a9x5l
mackeb
> Am I right in saying that the throttle body on a spreadbore is similar in
> operation to a Quad re the secondaries?? But a square bore, all 4
> butterflies open at the same time?
No. Both the spread and square bore carbs, as well as the QJet are
progressive - ie the primaries open before the secondaries under medium
to heavy throttle and the primaries only (generally) stay open at
cruising speeds.
Bear in mind that the QJet has mechanical seconadies with a vacuum
actuated air valve system that makes it pretty hard to under or over
carb just about any Holden V8 set up.
I run a QJet on both my 253 VH Commodore and 308 HJ and wouldn't go
back to a holley for anything. Both took some fiddling to get right.
The biggest problem was the APT setting wasn't right for the 308 as the
carb came off a 400 sbc from pontiac firebird.
May I ask what the problem with the QJet is?
Flat spots under hard acceleration but not under soft acceleration are
often air valve preload probs and can be sorted in no time! APT is
also quite a big factor in performance and economy.
Dre
Yep, thats exactly what I've got, 14" low profile and a 3" filter installed
in there. I also checked a quad last night and they have a similar setup
for the choke butterfly.
Nice, no worries then.
650 Spreadbore vac secondaries it is!
Thanks for the info!
Cheers Dre
Dre
news:1161089936.6...@b28g2000cwb.googlegroups.com...
I dont have any flat spots. I have extreme trouble getting the idle and off
idle circuit sorted. The 308 has quite a hot cam in it and it doesn't have
a lot of manifold vacuum at idle. I've played around with the spring on the
primary meetering rod plunger and have gotten it better, but its still not
right. You can feel the engine working through heaps of fuel and its
running too rich.
On top of that, whenever I floor it and open the secondaries, when I've
finished, the idle is around 700rpm higher than it was. Kill ignition,
start engine, idle back to normal. Open secondaries, idle raises again,
kill ign, start eng, idle normal again.
Cheers Dre
mackeb
> I dont have any flat spots. I have extreme trouble getting the idle and off
> idle circuit sorted. The 308 has quite a hot cam in it and it doesn't have
> a lot of manifold vacuum at idle.
Fair enough I suppose. Holleys are quite a bit easier to setup for low
vacuum systems, especially with the range of booster venturies
available.
The QJet certainly can be made to work in this situation but requires
drilling etc of fuel passages so you run the risk of rooting the carb.
Have you considered drilling a small hole on each of the primary
throttle plates (on the same side of the shaft as the transfer slots)?
This will allow more air in at idle. This is quite often performed on
cars with QJets and wild cams.
Later model emission carbs had smaller curb idle discharge ports.
Idle feed resistrictions may also need to be elarged.
John McKenzie
nope. Even on a squarebore (some dominators are exceptions, but they are
a different thing again0 the primaries (assuming both are double
pumpers) will still open about 2/3 of the way before the secs start to
open.
The actual difference is the _size_ of the throttle plates and venturis.
On a squarebore, the primaries and secondaries are roughly the same size
as one another. On a spreadbore, the primaries are noticeably smaller
(for more throttle response and better fuel efficency at low rpm and
throttle openings) and the secs are bigger.
In theory the spreadbore is a fucking much better option for a streeter.
In practice, holley made the spreadbore, not so much for these benefits,
but purely to have a carb that fit the bolt pattern of the rochester and
carters to get some gm and mopar guys to take a look who mostly used one
of the others from the factory. furthermore, holley for some fucking
unknown reason decided to re-route the acc pump circuits within the
metering block and the fuel bowls, fuel bowl gaskets and indeed metering
blocks are different and non interchangeable with squarebore ones. To
make it even worse, the sealing for the acc pump isn't the metering
block gasket itself, but an added tube and o-ring setup which tends to
dry and shrink if left standing long enough and also be a bitch to
separate. The acc pump squirters are _also_ different and non
interchangeable. the squarebore ones will fit, but they aim the spray in
the wrong place!
Then, the next issue is the floats. all of the spreadbores I've seen
have side hung and non externally adjustable floats. Which are just a
fucking pain in every way. Especially if you have trouble getting
re-usable fuel bowl gaskets (they _are_ available, but not many places
stock them. Even knowing exactly what I wanted, and going through this
with a particular wholesaler, they still stuffed it up and I was 3
months getting the right gaskets and so forth for the bloody thing)
So after all that, _if_ you sort all that, they are just able to do the
job a normal holley will. You'd _never_ pick (via performance or
economy) the difference between a well setup spreadbore or squarebore,
the spreadbore is just a lot more aggro to get sorted due to parts
availability. I haven't tried hume performance for the gaskets, but if I
had to do this again, I would, as they seem to be the only people that
really do everything hands on and know their stuff intimately. They tend
to be decent value too - a lot of local shops won't reco carbs and just
order through them as they can't justify the time spent.
If I was in your shoes, I'd actually try and find someone to sort the
quaddie. They are harder for a beginner to setup, and I'm not an expert
(and I've got enough holley bits and experience) but I could get the job
done if need be. the thing is, with any of the big 3 carb makers
(including the edelbrock clones of quaddies or carters) - any of their
carbs well sorted are so close to one another in potential as to be
indistinguishable. The _real_ issue is to actually make sure you _can
and do_ get them optimised for the setup.
If carbs are new, and it's hard to get bits or work done, then a holley
would be an easier starting point. I'd suggest a 600 squarebore vac sec.
mostly because it's a reasonable size match (and for what it might miss
on top end - the odd couple of percent at most, you'd never miss it, but
it's much easier to get it sorted acceptably in the mid range. And think
of that as being paramount. An engine (even in racing) spends the 'guts'
of it's time in the mid range, and only sees peak rpm just before the
gearchange, or at the end of the strip or straight, peak power
practically of zero concern)). 600 vac secs are also one of the most
common and cheapest holleys to find s/hand.
If you absolutely don't want to have to do any (or fuck all) sorting and
reco work, then the 570 holley street avenger (usually somewhat
competitively priced - check both hume, vpw and rocket and even play one
against the other to get the best price) wouldn't be a bad option. They
are basically a well setup 600 (for lack of better comparison) with
quick chance vac secondary spring, and very neat finish to them. You'd
likely get it to run quite well as is out of the box. (not that I'm
suggesting that anyone ever should, just saying you won't be stranded
with an undrivable pig before you get it sorted out)
Neil Fisher
<jm...@alphalink.com.au>, after considering some belly-button fluf,
wrote:
[...]
> I haven't tried hume performance for the gaskets, but if I
>had to do this again, I would, as they seem to be the only people that
>really do everything hands on and know their stuff intimately.
Have you tried Carby Services, John? They have a couple of *really*
good carby people (especially Al). Not to knock Humes, you understand,
but if you're looking for people who know carbies, IMO you can't go
past CSC.
Neil
---
Neil Fisher / Bob Young
Thundercords
personal opinion unless otherwise noted.
Looking for spark plug leads?
Check out http://www.magnecor.com.au
Dre
Yes I've got HEAPS of info from various sources but I was never keen on
drilling passages etc.
I totally admit the problem with the carb is the tune, but thats the
problem, I cant find anyone that *can* properly tune it. I can however get
the Holley tuned spot on.
Cheers Dre
Dre
Thanks very much for a very detailed answer. The problem for me is I cannot
find anyone that can tune a Quad, period and I've been looking for ages.
I've finally given up as the quad is in my ute and it shits me to tears, I
want to enjoy this thing and that carb is the major sticking point. I do
plan to install an EFI setup on this engine, but I need something in the
mean time and the quad isn't cutting it...
I can get a Holley tuned spot on *and* I have a use for it after I'm done
with it in the ute so I've decided to do the changeover.
Planning to go a reco 650 spreadbore vac secondaries...
Cheers Dre
Noddy
> I totally admit the problem with the carb is the tune, but thats the
> problem, I cant find anyone that *can* properly tune it. I can however
> get the Holley tuned spot on.
And herein lies the problem.
You can get a rotty to perform very well, but doing so is a task. As you say
it requires physical modification of the carb itself, and if you make a
mistake the thing is rooted.
A Holley will give you as good or better performance, doesn't been to be
drilled, has *vastly* superior support in terms of parts & accessories and
are relatively simple enough that the average Joe can get one working pretty
well without a detailed knowledge of them.
For these reasons, I've never understood why anyone would bother with a
Quadrajet. Still, some people just *like* to be different for the sake of
it.
--
Regards,
Noddy.
John McKenzie
>
> On Wed, 18 Oct 2006 19:51:06 +1000, John McKenzie
> <jm...@alphalink.com.au>, after considering some belly-button fluf,
> wrote:
>
> [...]
>
> > I haven't tried hume performance for the gaskets, but if I
> >had to do this again, I would, as they seem to be the only people that
> >really do everything hands on and know their stuff intimately.
>
> Have you tried Carby Services, John? They have a couple of *really*
> good carby people (especially Al). Not to knock Humes, you understand,
> but if you're looking for people who know carbies, IMO you can't go
> past CSC.
I haven't as yet. I've never been in the market for actual work to be
done, just good prices on parts (and the ability to know what I'm
actually asking for)
I could rattle off a list of names in melbourne where I've rung up
askign specifically for spreadbore bits, taken the time to double check
that it's definitely spreadbore, not the std squarebore etc etc, only to
get to the place and find, the contrary. Which ended up making _me_
quite contrary :) . Hell one of the main wholesalers (and supposedly one
of the top holley guys) down here used to tell everyone that certain
spreadbore parts were nla, and tried to sell squarebore reco or new
carbs, until I mentioned to him I had been in touch with holley in the
USA and they were still making the parts 'yes, but you'd have to order
them in special, I don't normally stock them'. Which is a far cry from
nla and buying a new carb. I'd hate to think someone would actually have
fallen for that prick's scam.
If I was born in another era, I think I might have done well with a
carby business. I have no idea if they were money winners way back when,
but they generally made perfect sense to me just by looking at them and
thinking. Dunno why, as there's plenty of things I look at that
absolutely don't...
I did a quick google for them but couldn't get a hit (that looked
remotely right) - could I trouble you for their details?
John McKenzie
> The problem for me is I cannot
> find anyone that can tune a Quad, period and I've been looking for ages.
Fair enough too - that's absolutely a case of 'bird in the hand' (except
that it's really like a bird in the hand or one in the bush, since the
'quaddy in the bush' isn't potentially significantly better than a well
setup holley) so there's real sense in that.
> I've finally given up as the quad is in my ute and it shits me to tears,
fair enough too. Since neither you, the engine, nor anyone else would
know what carby is under there (provided it's well sorted) there's no
reason to stick with an unsortable (given your circumstances) carb.
I
> want to enjoy this thing and that carb is the major sticking point. I do
> plan to install an EFI setup on this engine, but I need something in the
> mean time and the quad isn't cutting it...
The thing I _would_ consider is removing the inlet manifold, and
touching up the holes under the carb in the std manifold with a die
grinder to remove rough edges and smooth the flow transition from the
base of the carb into the inlet manifold. It can reduce fuel separation
at those sharp edges and allow the engine to run well with leaner jets,
as there's better fuel distribution/uniformity.
> I can get a Holley tuned spot on *and* I have a use for it after I'm done
> with it in the ute so I've decided to do the changeover.
Makes sense to me.
>
> Planning to go a reco 650 spreadbore vac secondaries...
Ok, depending on the specific combo (feel free to list the details
again) you might run into one slight snag. the cross to bear of holley
vac secs is that they don't open like carters and rochesters. On the
other two, the throttle open, but a big air door above them (where the
choke would be more or less on the primaries) is closed, but biased in
it's weight and shaft location. Air flowing down in there (or trying to)
opens the air door. Since it's over the main fuel metering spot in the
secs, it acts like a choke whilst they are opening, and automatically
enrichens the mixture. So it has an automatic sort of secondary acc
pump. It allows the secs to be opened relatively quick.
On the holleys, when you open the throttle, it slides a link arm along
the secondary throttle linkage which then allows the secs to open, but
doesn't open them itself, it just 'puts some slack in the line' so to
speak. the vac cannister will then work to open them. If you lift off
the throttle, the link arm pulls tight and closes the secs no matter
what the cannister wants to do.
this means there's no secondary enrichment. So as holley secs (vac
operated ones) open there's no enrichment going on. so they lean out a
little. The faster you open them, the more the lean out, to the point of
a flat spot. It's basically the down time between when the secs open and
when the secondary fuel circuits fully respond to the increase in fuel
flow..
SO this leanout doesn't mean it's overcarbed, it just means it's
desperately in need of an acc pump for the secs (or a substitute). This
is _very_ important.
If you run a different spring in the cannister, a heavier spring, the
secs won't open az much for a given suction, as the spring resists. So
it doesn't as much affect how quick the secs open, it affects how _far_
they open. By going to a stronger spring (as per holley recommendations)
you limit how far it opens. This _will_ almost always get rid of the
flat spot. But it also means the stronger spring is stoppign the secs
opening further (or fully) and once the fuel flow has gotten over that
initial hurdle, esp the higher the rpms climb, it will actually _want_
more airflow than that spring would allow.
Which is problem enough on a squarebore. On a spreadbore the secs
account for a much greater percentage of flow, so the leanout will be
more severe, and the stronger springs will cut of even more of that
greater proportion of flow. Meaning you can (left unchecked) end up with
a fair compromise in output above mid range rpms.
Obviously what _needs_ to be done is not to limit the extent the secs
open, but how quickly they do so (or slowly as the case may be). The
solution is simple enough. In the vac cannister there's a check ball, it
lets air in one way (pops off the seat) and slowly the other (it sits on
the seat, and the air only flows through grooves around it). That's to
help lower stress on the vac diaphragm when it has high vac, but the
throttle is lifted off and it yanks the secs closed.) You _could_ just
as easily have a restrictor in the passage (tiny sleeve) and it'd be a
little more stress on it, but you could always put in a new diaphragm
every couple of years, consider it a routine thing done perhaps when you
flush brake fluid (I tend to do that yearly, I don't know too many who
do, more's the pity).
What you do is make the hole/restriction even tinier (you can heat the
base/cup the ball sits in and tap the ball a few times with a hammer to
flatten out the base and reduce the depth of the grooves as it will sit
a little lower, if that makes sense, or just add a restriction in the
vac port somewhere, which is what I tend to do. The other thing you
could do is simply drill into the vac cannister lid (carefully) and
attach a hose barb, then run a short hose to a small container, maybe
something like a fuel tank of a model car and seal that off. The extra
time to pull vac out of the mini tank will slow the opening rate.
Personally I'd go the 'make your own restriction' in the vac port, as
it's the easiest to do, and to alter or remove later on.
That way you end up with slower opening secs, but no flat spot, which
mean you can run a lighter spring which will open them up more
(eventually) at higher rpm, and not restrict the mid-range on up. You
don't generally see that in holley literature, but it's kosher, I assure
you.
The other thing to consider is not so much a bigger acc pump squirter
(it might be necessary for other issues, but not specifically for this
one), but looking at a cam with more delivery right at the end of the
primarly linkage travel. This will give a larger squirt right at the
end, adn help alleviate any potential lean out as the secs start to
open.. I'm not sure which one comes with the 650 spreadbore std (though
I bloody should, I've got the remains of one sitting around here
somewhere) but there is a chart you can download from holley (let me
know if it's impossible to find) that shows the various delivery
idosynchrasies of each colour acc pump cam. Yet another thing that could
be done is to make (potentially via a similar method) the high speed air
bleeds on the primaries slightly smaller, which would theoreritcally
make it run a little richer on the primaries at higher throttle
openings, but also help alleviate the lean out.
Naturally enough, if the flat spot is non existant, the above stuff
isn't a big deal. But if there is a flat spot, and it's not (or just
barely) sorted with the strongest spring in the vac cannister, the above
stuff is well worth a thought. As a dumb example, a friend's son put a
600 on a nearly stock 253. I became involved because he'd swapped the
old 2 barrel and some cash for the 4 barrel and inlet. And needed to get
it sorted before his old man found out and murdered him. With the
heaviest spring in there, it just barely fixed the flat spot.
Some or all of this comes up in a big series of posts on performance
forums. It may or may not help:
http://www.performanceforums.com/forums/showthread.php?t=67196864
mackeb
> For these reasons, I've never understood why anyone would bother with a
> Quadrajet. Still, some people just *like* to be different for the sake of
> it.
Spot on. I like the QJet though because when it is right (or close to)
then it absolutely blow the holley out of the water for power, smooth
throttle response etc and the fuel economy is fantastic.
I do agree with the comments about drilling etc. There are not too
many things you can drill and completely stuff up the carb, it would
just be time consuming to repair and I suppose with the cost of QJets
going through the roof this can only be a bad thing.
I am luck enough to own two 800 cfm (large primary) QJets and found
that these work really well, even with the jets to suit a 400 sbc on my
308. Low end torque is good and mid to high end throttle response is
off the chart. You think the secondaires are open, then you squeeze
the pedal a bit more and yeee harr ;-))
{Insert comment hear about how much better a 350 would be ;-))) }
Interesting QJet fact: QJets were fitted to the ford cobrajet from the
factory (don't know what yar though).
Noddy
"mackeb" <mac...@cen.prendiville.wa.edu.au> wrote in message
> Spot on. I like the QJet though because when it is right (or close to)
> then it absolutely blow the holley out of the water for power, smooth
> throttle response etc and the fuel economy is fantastic.
Like fuck it will :)
Only someone who has never been within 5 kilometers of a well set up Holley
could ever make this statement :)
> I do agree with the comments about drilling etc. There are not too
> many things you can drill and completely stuff up the carb, it would
> just be time consuming to repair and I suppose with the cost of QJets
> going through the roof this can only be a bad thing.
The fact that you have to drill them at all makes them a pain in the arse,
and opens up a world of potential scrap alloy for those who aren't so
particularly skilled.
You might think something as simple as drilling a hole couldn't end in
disaster, but there are people out there who can turn it into a CNN worthy
news story.
> I am luck enough to own two 800 cfm (large primary) QJets and found
> that these work really well, even with the jets to suit a 400 sbc on my
> 308. Low end torque is good and mid to high end throttle response is
> off the chart. You think the secondaires are open, then you squeeze
> the pedal a bit more and yeee harr ;-))
>
> {Insert comment hear about how much better a 350 would be ;-))) }
I think a 660 centre shooter would be much better, but I'd never insult one
by putting it on a plastic when a WW Stromberg would suffice :)
> Interesting QJet fact: QJets were fitted to the ford cobrajet from the
> factory (don't know what yar though).
There were a number of Cobra Jet Fords, and a version of the Rotty was only
ever available as a stop gap measure on one of them, and that was the 1970
429 cubic inch version.
Ford has used a number of carburettors over the years, from Holley,
Autolite, Carter, and their own (which was a version of the autolites that
they made themselves). Their basic principle towards carbs was that anything
low performance got a 2 or 4 barrel autolite (later a "Ford" carburettor,
and later still a Carter), and anything high performance got a Holley right
off the bat, ranging in CFM values from 600 to 850.
The single Rotty equipped '70 429 was a dealer fit "package" that existed
for a very short time when Ford had trouble supplying cars with non
performance 4 barrel carbs after Autolite was wound up and Ford themselves
had not yet got their own carburettor manufacturing into full swing. To tide
them over, Ford did a deal with Rochester for them to supply a very small
number of 715 cfm carbs that were to be fitted until the hold up with
production was sorted.
As it turns out, 99% of people who ordered a 429 Cobra jet in 1970 did so
with the 750 cfm Holley, and the Rochester equipped car became very rare
indeed.
Every other Cobra Jet (or performance Ford of any type for that matter),
came standard with a Holley, and Ford's association with Holley goes back to
the days of the Model T.
--
Regards,
Noddy.
John McKenzie
>
> and I suppose with the cost of QJets
> going through the roof
are they seriously? I recently gave away a pair of them! doh!
Dre
<snip> Holy crap! I kinda wish you hadnt told me all this, they sound just
as finicky as a Quad :)
I totally hope I dont have a flat spot, but have saved all of this
invaluable info incase I do, thanks very much for putting it all down.
Maybe I just stick the ute into the garage now and start the efi, LOL!
Cheers Dre
Dan---
> Dan--- <iam...@nospam.com> wrote:
>> "Athol" <m...@privacy.net> wrote:
>
>>> Just to keep John McK happy, I haven't mentioned the brand of mixer.
>>> :-)
>
>
> Why would I want to piss him off?
Missed the ;-) did we?.
I dunno I kind of enjoy reading Johns ramblings very comical. :-)
--
Regards
Dan
Neil Fisher
>I did a quick google for them but couldn't get a hit (that looked
>remotely right) - could I trouble you for their details?
Carburettor Service Co.
240 Parramatta Road Burwood NSW
02 9747-4066
Ask for Al or Tim. Tell them I said to ring.
Neil.
John McKenzie
> isn't a big deal. But if there is a flat spot, and it's not (or just
> barely) sorted with the strongest spring in the vac cannister, the above
> stuff is well worth a thought. As a dumb example, a friend's son put a
> 600 on a nearly stock 253. I became involved because he'd swapped the
> old 2 barrel and some cash for the 4 barrel and inlet. And needed to get
> it sorted before his old man found out and murdered him. With the
> heaviest spring in there, it just barely fixed the flat spot.
I managed to forget to finish that paragraph. After the mod to the vac
port to make even more of a restriction, we went 3-4 springs lighter and
it still had no flat spot. The difference above 3500rpm was noticeable
enough by seat of the pants (and without being a tool, i can generally
discern between improvements and other factors that might make it appear
to have improved). On particularly large engines, you can actually get
to the point where they have no trouble developing significant signal
strength and you can even open up the existing factory restriction and
open the secs quicker without a flat spot occuring.
Incidentally the air-door setup is _the one true thing_ the carters and
rochesters have over vac sec holleys. If it was for a race engine (or
very serious streeter) the double pumper holleys (which have the
secondary acc pump thus enabling the secondaries to be opened
instantaneously without a hesitation) are definitely the go.
I still maintain that well setup there's fuck all between any of them,
and provided the carb sizing was reasonably appropriate, any one of them
could be made to work. It's more a case of if I was starting from
scratch, and cost differences didn't factor in, I'd go for the holley
for most race stuff, and probably street, but if I got a carter for free
(or possibly a rochester) I'd not turn it down.
About the only exception to this is the carter thermoquad. They are
actually a particularly well thought out carb in terms of function and
tunability (and indeed flow) but part of them (and the fuel bowl section
is integral) is made out of some sort of bakelite or plastic (I don't
know exactly what) and it _is_ prone to cracking. I used to work at a
damaged vehicle auction, and more than a few of the older fords that
were in there were because of underbonnet infernos, and the remains of
the thermoquad were plain to see. If you can get them new (I honestly
don't know) then I wouldn't object, but no way known you'd get me to
settle for a s/hand one. Too much to lose.
Out of curiousity - have you read any literature on the quadrajets.
There's a reasonably good book by (I think) doug rowe. I've actually got
it lying around somewhere. you're welcome to borrow it (but be advised,
it might take me a good 2 months to find, and then manage to get it in
the mail or whatever!)
I've not read them, but 'too many' people have praised holley books by
dave emmanuel for it to be a fluke - if you were in the market for a
holley tweaking book, he's the author I'd look to. I don't have personal
experience there, as I've mostly done the 'suck it and see' learning
method with holleys (and seemingly prevailed).
Only other thoughts - if you do go efi - please please please, find a
set of efi spec heads and go that way. Even stock cast iron factory efi
heads flow as well (and often better) as the most heavily ported pre efi
heads. Yes, you need to change to a different inlet to suit, as well as
different exhaust headers (castle auto electrics make them to suit any
pre efi car with efi heads mind you) and of course revised cam due to
different inlet and exhaust layout, but in the long run you get a much
nicer package.
Where it gets really 'funny' is that the factory std inlets for the 304s
aren't exactly the best breathing setups around. You can actually make
more power with a torquepower inlet manifold (they are the clear cut
king of carb style inlets for efi heads, but they can run with efi as
well) and a well sorted carb than with efi on the stock efi inlet! I'd
even go as far as to say you might end up with a torquepower inlet and
decent carb and end up not even bothering with efi (it was certainly the
experience of the guy who had the 253 that got the 600 vac sec with mods
by me. It ended up with a 308 torquepower inlet, efi heads, blah blah
blah and runs low 13s (possibly good for a 12 if he can get it off the
line better) with a 3.25 diff and 2500convertor (he pulls around 2800rpm
at 100km/h with the tyre height he has) for comparison sake, in a HQ
coupe with probably 500kg extra of stereo and various other dubious
accessories over the std coupe.
John McKenzie
> Carburettor Service Co.
> 240 Parramatta Road Burwood NSW
> 02 9747-4066
> Ask for Al or Tim. Tell them I said to ring.
Thankyou muchly. I don't know when the next 'exciting carby adventure'
will be, but I'll certainly give them a call when it pops up.
Dre
Yep, there are 2 of those books, a new revision and an old. I have both :)
> I've not read them, but 'too many' people have praised holley books by
> dave emmanuel for it to be a fluke - if you were in the market for a
> holley tweaking book, he's the author I'd look to. I don't have personal
> experience there, as I've mostly done the 'suck it and see' learning
> method with holleys (and seemingly prevailed).
>
> Only other thoughts - if you do go efi - please please please, find a
> set of efi spec heads and go that way. Even stock cast iron factory efi
> heads flow as well (and often better) as the most heavily ported pre efi
> heads. Yes, you need to change to a different inlet to suit, as well as
> different exhaust headers (castle auto electrics make them to suit any
> pre efi car with efi heads mind you) and of course revised cam due to
> different inlet and exhaust layout, but in the long run you get a much
> nicer package.
I allready have VS commodore heads, a mild Crow cam (which the engine
builders kindly lost the specs for!!) and extractors to suit. I'd be using
a stock VS commodore EFI manifold and setup. I've allready mounted the fuel
lines, but still need to install the fuel pump and filter up the back.
Then I need to work out how to get around the body control module (I have a
lead) and install it all. But there are a quite a few little shit things I
need to sort before I can start, otherwise the utes not going anywhere...
> Where it gets really 'funny' is that the factory std inlets for the 304s
> aren't exactly the best breathing setups around. You can actually make
> more power with a torquepower inlet manifold (they are the clear cut
> king of carb style inlets for efi heads, but they can run with efi as
> well) and a well sorted carb than with efi on the stock efi inlet! I'd
> even go as far as to say you might end up with a torquepower inlet and
> decent carb and end up not even bothering with efi (it was certainly the
> experience of the guy who had the 253 that got the 600 vac sec with mods
> by me. It ended up with a 308 torquepower inlet, efi heads, blah blah
> blah and runs low 13s (possibly good for a 12 if he can get it off the
> line better) with a 3.25 diff and 2500convertor (he pulls around 2800rpm
> at 100km/h with the tyre height he has) for comparison sake, in a HQ
> coupe with probably 500kg extra of stereo and various other dubious
> accessories over the std coupe.
>
> --
> John McKenzie
Thanks again for the info. My setup is as follows (bearing in mind I
haven't built this thing to be a race car, I'd like a nice streetable ute).
Its a HZ ute, 308 bottom end, VS commodore heads and EFI manifold, Pacemaker
extractors through a twin 2.25" system, Supra 5 speed, 3.08 diff. It sits
at around 2600 rpm at around 118k/h in 5th gear which is bloody great (I do
a fair bit of highway driving). 1st gear is basically tire smoke, it
currently lights up the rears in 2nd when you dump the clutch, 3rd gets it
to around 155k/h and I haven't wound 4th out :)
BUT its an absolute dog around town, it wont idle very well and when you
open the secondaries it goes like stink (literally) and puts out shitloads
of black smoke (rich fuel).
Cheers Dre
mackeb
> > and I suppose with the cost of QJets
> > going through the roof
>
> are they seriously? I recently gave away a pair of them! doh!
>
Yep. Second hand average condition ones are going for $100-250 here in
Perth with recond. carbs going for ~$450
Arnie
> > Dre wrote:
> >> "matt vk3zmw" <nos...@nospam.ever> wrote in message
> >> news:F3IYg.48107$rP1....@news-server.bigpond.net.au...
> >>
> >>>Dre wrote:
> >>>
> >>>>Hi all, I should know this, but does a square bore carb fit a spread
> >>>>bore manifold??
> >>>>
> >>>>I'd like to pull the (buggered) quad off a 308 with spreadbore
manifold
> >>>>and stick a squarebore holley on it, is this possible??
> >>>>
> >>>>Cheers Dre
> >>>
> >>>Cheap option: Edelbrock spreadbore carby w/ vac secondaries.
> >>
> >>
> >> problem is they are even harder for me to find than the spreadbore
> >> holleys!
> >>
> >>
> >>>better option: bolt-on Holley or Edelbrock throttle-body injection.
> >>>
> >>>BTW, how do you know the quaddy is buggered?
> >>
> >>
> >> I've spend ages on it and too much money, I cant find anyone that
really
> >> knows them and its still running like a piece of shit so its going.
Too
> >> inconisitant. I've tried, failed so going back to what works (or what
I
> >> can make work anyway)
> >>
> >> Cheers Dre
> >
> > Hahahaha yep it's a quaddy alright. When somebody that can tune them
does
> > it right they are a brilliant carby, until they are tuned correctly they
> > can be a total PITA, which is generally about 90% of the time...
> >
> > Adam
>
> Yep, totally agree, and I've been fiddling with it for ages (waaaay to
long
> :)
>
> To cut a long story short, I'm planning to stick an efi manifold from a VS
> commodore on the engine (the engine allready has VS heads, cam and
exhaust)
You have a quadrajet on VS heads? what manifold?
John McKenzie
I'll see how many I've got - I might still have a couple left - if you
know of anyone I'll go halves with you.
John McKenzie
Hangon, I'm losing the plot - this is the one with the quaddy currently
on it? Which inlet have you got on there?
Or are the efi heads about to go on it (apologies, I'm not with it
today, Anyone got a day job they wanna offer me?)
> BUT its an absolute dog around town, it wont idle very well and when you
> open the secondaries it goes like stink (literally) and puts out shitloads
> of black smoke (rich fuel).
Is there any chance at all that the throttle shafts are worn a fair bit?
That's what I'm thinking. Possibly exacerbated by the location of the
return spring.
If the spring is on the opposite side of the link arm (across the other
side of the throttle shaft) the spring and the cable (or link arm) pull
on one another in a see-saw like motion. With time, this grinds away at
the throttle shaft.
The only way to prevent it (and sadly more than a few factory setups are
'wrong' on that front) is to move the spring to the same 'end' of the
linkage so it the cable or link is attached to the top and pulling
backward, the spring needs to be attached at the top and pulling forward
NOT attached to the bottom and pulling rearward.
If the throttle shaft and carb base is worn, not much will help, but
relocating the spring will tend to pull it closed more uniformly, and to
the same spot each time. Right now (if it's 'wrong') it'll pull back but
have a few sticking points along the way, and not quite shut, then as it
cools down, or is left, with the minute amt of expansion and then
contraction, it often will pull itself that last few thou home. Giving
you the problem you have now.
I should have probably mentioned that earlier. It's a prick of a thing
too. a few HQs with sb chevs and similar that I've seen have exactly
this problem, partly due to factory inlets, but also because there's not
_too_ many conveniant places to put the spring toward the front (one
trick it to make a loop of thick steel wire, and run it around the temp
sensor (there's a right way and a wrong way to do that obviously). but I
can't think if it would even come up as a drama on the holden or not
without one in front me to reacquaint myself with the inlet manifolds.
--
John McKenzie
mackeb
> I'll see how many I've got - I might still have a couple left - if you
> know of anyone I'll go halves with you.
I'll take em if they're not too expensive. You can never have too many
QJets ;-))))
Do you have any large bore primary jobbies lying around?
Dre
news:4539...@dnews.tpgi.com.au...
Cheers Dre
Dre
The quad is currently on a 308 in my ute, the 308 has VS heads, a cam and
pacemakers to suit those heads, and an inlet to suit a carb with EFI heads.
The inlet is a Redline single plane manifold for carbs to suit EFI heads.
When I got the engine built I wanted to be able to convert over to EFI
easily in future.
What you've said below is spot on, there *is* play in the shaft and it was
very hard for me to find a spot for that spring. I have a few other quads,
all the throttle bodies are average so not worth changing.
Buuuuuuuut, on Friday I scored a reco double pumper 650 vac secondary
spreadbore for cheap! So now the quad is gone :)
When it arrives, I plan to find out the jets/valves in it and then for shits
and giggles, just plop it on there and see what happens :)
I fully expect it to be a bit of a pig (especially since it has unknown
jets/valves), but I'll sort it once its on there, it cant be any worse than
my current quad.
Btw, do you know any good Holley tuning books? I'm going to have a go at
sorting this out myself before I hand it over.
Cheers Dre
John McKenzie
>
>
> Buuuuuuuut, on Friday I scored a reco double pumper 650 vac secondary
> spreadbore for cheap! So now the quad is gone :)
Is it double pumper or vac sec? I think you've made a typo as it can't
be both!
> When it arrives, I plan to find out the jets/valves in it and then for shits
> and giggles, just plop it on there and see what happens :)
As a warning, even if re-cod be careful getting the fuel bowls off, as
they tend to stick badly (esp with paper gaskets) and then extra careful
if you want to take the metering blocks off. Due to the
shape/location/design of the acc pump transfer tubes that fit inside a
passage in the metering block and carb main body, and they seize up to
buggery.
> Btw, do you know any good Holley tuning books? I'm going to have a go at
> sorting this out myself before I hand it over.
I've not read them myself (never actually read any books on holleys) but
there's consensus from anyone who's anyone that the books by Dave
Emmanuel (I think released under HP books) on holleys are the business.
I dare say you'd be able to get second hand for a song from amazon.com
or new if preferable.
There's probably a bunch of posts from the past couple of years in
aus.cars that would give a step by step. I'm thinking off the top of my
head either myself or John H might have been the most recent.
John McKenzie
Aside from the more prevalent throttle shaft issue, I dare say that
you'll find that that inlet in and of itself isn't all that crash hot.
I'm not shitting on it because it's a redline product. I'm rather
focusing on the fact that a single plane inlet shows less signal
strength (and hence more difficulty in optimising or even the
potentially lower overall result even when fully optimised) which
affects the drivability and even the performance at lower rpms.
Of the available it's probably in 3rd place (behind the harrop in 2nd,
and the torque-power as #1). If you were starting from scratch, and I
harp on this because it really is sensational, then the torquepower dual
plane is outstanding. Very good low-mid range, and it 'holds on' much
higher in the rpm range. In other words, you'd probably _never_ have an
even slightly streetable combo that the dual plane torquepower is not
ideal for. The single plane they make (esp the newer one) is kickass,
but I personally would suggest it's more race only oriented.
I should've put this in one of the other posts - but this reco
spreadbore you are getting - if it's from a carb shop somewhere, see if
they'll send it to you with re-usable fuel bowl and metering block
gaskets. They really are re-usable, even years down the track come apart
and back together with ease and re-seal perfectly. They also mean you
don't have to scrape paper ones off (which can take more time than the
rest of the reco work put together). Best of all, I once had an issue
that drove me up the wall with a holley, and it was down to some tiny
bits of gasket debris winding up in one of the fuel circuits. Took
forever to trace.
If it can't be ordered with them, let me know, I'll dig up the 'right'
part numbers for the spreadbore spec reusable gaskets (I wrote them down
after the trials and tribulations I had the last time around)
Dre
I totally agree. I speced a Harrop dual plane manifold to begin with and
when I went it to check how it was all going, they had allready fitted a
bloody redline POS single. By that stage I had had enough of their shit and
just wanted my engine finished and out of there. Dont get me started on
that place, absolute nightmare it was.
> Of the available it's probably in 3rd place (behind the harrop in 2nd,
> and the torque-power as #1). If you were starting from scratch, and I
> harp on this because it really is sensational, then the torquepower dual
> plane is outstanding. Very good low-mid range, and it 'holds on' much
> higher in the rpm range. In other words, you'd probably _never_ have an
> even slightly streetable combo that the dual plane torquepower is not
> ideal for. The single plane they make (esp the newer one) is kickass,
> but I personally would suggest it's more race only oriented.
I'm not really fazed about the manifold at this stage as I have an efi
manifold, this is just an "in the mean time quick fix", so if I can get the
holley close, that will do. Once I fit the efi, I put a for sale sign on
the redline and move the Holley onto a 308 with L34 heads and a 4 barrel
dual plane manifold. This engine hasn't been finished yet (I still need
some parts for it too) anyway but once I fit the Holley, then I spend some
serious effort to get it running properly.
> I should've put this in one of the other posts - but this reco
> spreadbore you are getting - if it's from a carb shop somewhere, see if
> they'll send it to you with re-usable fuel bowl and metering block
> gaskets. They really are re-usable, even years down the track come apart
> and back together with ease and re-seal perfectly. They also mean you
> don't have to scrape paper ones off (which can take more time than the
> rest of the reco work put together). Best of all, I once had an issue
> that drove me up the wall with a holley, and it was down to some tiny
> bits of gasket debris winding up in one of the fuel circuits. Took
> forever to trace.
>
> If it can't be ordered with them, let me know, I'll dig up the 'right'
> part numbers for the spreadbore spec reusable gaskets (I wrote them down
> after the trials and tribulations I had the last time around)
That would be bloody great, hugely appreciated, thanks very much!.
Btw, I have a 4175 spreadbore Holley.
Cheers Dre
Dre
> Dre wrote:
>>
>>
>> Buuuuuuuut, on Friday I scored a reco double pumper 650 vac secondary
>> spreadbore for cheap! So now the quad is gone :)
>
> Is it double pumper or vac sec? I think you've made a typo as it can't
> be both!
Really? Shows how much I know about holleys :) Its definately a vac
secondary 650 (its a 4175 Holley), so not a double pumper. I was looking at
soo many different Holleys the other week I must have mixed them up.
>> When it arrives, I plan to find out the jets/valves in it and then for
>> shits
>> and giggles, just plop it on there and see what happens :)
>
> As a warning, even if re-cod be careful getting the fuel bowls off, as
> they tend to stick badly (esp with paper gaskets) and then extra careful
> if you want to take the metering blocks off. Due to the
> shape/location/design of the acc pump transfer tubes that fit inside a
> passage in the metering block and carb main body, and they seize up to
> buggery.
Roger that, noted! I have downloaded a few exploded diagrams so I now know
how its stuck together. It'll make a hell of a lot more sence once I have
the carb sitting in front of me..
>> Btw, do you know any good Holley tuning books? I'm going to have a go at
>> sorting this out myself before I hand it over.
>
> I've not read them myself (never actually read any books on holleys) but
> there's consensus from anyone who's anyone that the books by Dave
> Emmanuel (I think released under HP books) on holleys are the business.
> I dare say you'd be able to get second hand for a song from amazon.com
> or new if preferable.
Nice, thanks I'll have a look.
> There's probably a bunch of posts from the past couple of years in
> aus.cars that would give a step by step. I'm thinking off the top of my
> head either myself or John H might have been the most recent.
LOL, you mean all those posts I have been saving into my "useful posts"
folder over the years :) Yep, I'm reading everything I can atm!
Thanks again!
Cheers Dre
John McKenzie
>
> "John McKenzie" <jm...@alphalink.com.au> wrote in message
> news:453DAA...@alphalink.com.au...
> > Dre wrote:
> >>
> >>
> >> Buuuuuuuut, on Friday I scored a reco double pumper 650 vac secondary
> >> spreadbore for cheap! So now the quad is gone :)
> >
> > Is it double pumper or vac sec? I think you've made a typo as it can't
> > be both!
>
> Really? Shows how much I know about holleys :) Its definately a vac
> secondary 650 (its a 4175 Holley), so not a double pumper. I was looking at
> soo many different Holleys the other week I must have mixed them up.
I figured as much. I acutally suspected you meant vac sec, as you had
been focusing on that for hte most part. With the breadth of topics
brought up in this thread, the odd typo or two isn't unusual (hell I
left out the last half of a whole bloody paragraph in one post!)
>
> Roger that, noted! I have downloaded a few exploded diagrams so I now know
> how its stuck together. It'll make a hell of a lot more sence once I have
> the carb sitting in front of me..
I agree wholeheartedly. I don't know why, but a lot of line drawings
start to get hard to read (*maybe I have a form of dyslexia??) whereas
if I see something in the flesh, or a photo (as opposed to diagram) of
it I'm 100% able to 'get it' at a glance.
>
> LOL, you mean all those posts I have been saving into my "useful posts"
> folder over the years :) Yep, I'm reading everything I can atm!
>
god help us all!
Another thing I didn't bring up about the spreadbores, but have in the
past is that they have 'fixed' booster venturis. On the squarebores,
they are cast separate then slotted into the main body and locked in
place with a flared edge where the metering block meets the carb main
body. Which means you can change em for more sensitive ones. It also
means they can come loose (and often that's the cause of untraceable
fuelling issues on older ones). The spreadbore ones are cast into place.
So you can't change them. But what you might look at doing, if absolte
need be (and this is related to getting the secs to have more signal
strength) is drill them from the bottom up.
It requires you mod the tip of the drill bit to avoid cutting the centre
section out, and a very close matched drill bit diameter, and a sturdy
enough drill press to get it dead straight and also to exactly match the
depth.
But basically making the bottom half of the booster bigger, at the right
spot will lead to a little more signal strength and better atomisation
(esp if the size of either the carb as a whole, or the secs themselves
in this case, is borderline for the engine). Even if it doesn't have the
flat spot, some guys pursue it for better throttle response, and to be
able to open the secs on a holley vac sec even quicker.
I did a pic of this ages ago for a moparmarket post. It was about a
different carb, but the principle applies. Of couse the std holley
booster venturi have a 'roof' going across the top of the basketball
hoop which isn't shown here, but the rest of the venturi shape is close
enough.
In the pic on the left is the std booster. In the middle is what you'd
drill if you could custom make a cutting tip to do it. On the right is
the 'compromise' you do with a std drill bit. You have to leave the
narrowest section as is, as that actually develops most of the signal,
but the sharp and abrupt change to the bigger diameter below there helps
as well (it also arguably leads to mixture turbulence, for want of a
better term which improves fuel atomisation/distribution.
the drill bit A is a std bit. You'd need to modify it by grinding out
the centre section till it's curved like that. That way it won't start
to hit that roof section whilst drilling the booster. If that makes
sense. drill bit c doesn't apply in this case.
http://home.alphalink.com.au/~jmac/venturi%20mods.jpg
naturally if you stuff it up, it's a lot harder to rectify since you
can't replace them (unless holley has revamped the spreadbores and used
replaceable boosters, but not likely) as such