Is a 5-angle valve seat better than a 3-angle?
Thomas Hood
their Serdi equipment but I have never seen this offered before. Does
it flow noticably better? Is valve seat life compromised?
If 3 angles is better than 1 and 5 better than 3 is the perfect valve
seat a radius?
Tom
Dave Baker
>From: thoma...@virgin.net (Thomas Hood)
>Date: 17/04/02 17:47 GMT Daylight Time
>Message-id: <1712da36.02041...@posting.google.com>
>
>The Cylinder Head Shop here in the UK is offering this service on
>their Serdi equipment but I have never seen this offered before. Does
>it flow noticably better?
Nope, but it isn't really a meaningful question because the widths and angles
of each of the cuts and the resulting throat diameter are unknowns. 3 angles
that got these right would obviously be better than 5 that were all wrong.
Is valve seat life compromised?
Again, not a meaningful question. The width and angle of the seat part of the
cut isn't specified in either case. The angles either side of that are
irrelevant.
>If 3 angles is better than 1 and 5 better than 3 is the perfect valve
>seat a radius?
>
>Tom
Not necessarily no. Sharp edges between each of the cuts can actually be
beneficial. Airflow is a strange beast.
What matters is proper flowbench research and knowing what works and what
doesn't. All you're seeing is advertising bullshit.
Dave Baker
Puma Race Engines (www.pumaracing.co.uk)
Terry Thorne
used to cutaway material for better flow/breathing. most bang for the buck
on a V8 American engine is a windage tray.
good luck-go fast
tt
Dean Dardwin
Like a lot of things... it depends. On some heads, where a 5 angle cut
is possible, they will flow a little better. Will you notice the
difference on a low rpm street engine? Not likely. Will you notice the
difference on a high rpm race engine? Maybe. But the pro engine builders
use a flow bench to make sure.
Bottom line is that the accuracy of the valve job is more important that
the number of angles.
Dean
Rex Burkheimer
> it flow noticably better?
Maybe. Is this a racing engine?
>Is valve seat life compromised?
Not if the actual contact area stays the same
Any good shop cuts seats to 3 angles on a stock valve job. This just narrows
the seat to specs, since the first cut widens the contact area. Two more
angles just smooths the transition to the valve pocket and to the combustion
chamber.
If done intelligently, you can see some differences in the very highest
RPM range.
What do they do to the valve?
j.brew
knife edged, but the engine only lasts one race... :-)
Jb
"Thomas Hood" <thoma...@virgin.net> wrote in message
news:1712da36.02041...@posting.google.com...
Tom
Did you think to ask them why they offered this?
Tom
M/shop info & old machine tools.
http://shopswarf.orcon.net.nz
Jordan
engine in a British bike (700cc) stated that a multi-angle valve job was
essential on that motor, for good performance. Don't know how you could
have fewer than 3 angles.
7 is probably even better!
The Davenport's
In theory, yes...but that is a pretty hard theory to hit.
In a perfect world, a knife edge would be the best, but it's not going to
last very long...one race, no more...to make it last longer, a radius with a
very small, single angle would be best...small the contact, the better flow,
but the shorter the valve job is going to last.
A five angle grind is a more repeatable version of the radius...hard to
repeat the radius in the real world.
Luck
Mike
Dave Baker
>From: "The Davenport's" dav...@charter.net
>Date: 18/04/02 01:21 GMT Daylight Time
>Message-id: <ubs4ceg...@corp.supernews.com>
>
>
>"Thomas Hood" <thoma...@virgin.net> wrote in message
>news:1712da36.02041...@posting.google.com...
>> The Cylinder Head Shop here in the UK is offering this service on
>> their Serdi equipment but I have never seen this offered before. Does
>> it flow noticably better? Is valve seat life compromised?
>> If 3 angles is better than 1 and 5 better than 3 is the perfect valve
>> seat a radius?
>>
>> Tom
>
>In theory, yes...but that is a pretty hard theory to hit.
>
>In a perfect world, a knife edge would be the best, but it's not going to
>last very long...one race, no more...to make it last longer, a radius with a
>very small, single angle would be best...small the contact, the better flow,
I take it you don't have a flow bench then or you'd know just how wrong that
was. I suppose I shouldn't complain that so many people get valve seats wrong
because a fair chunk of my work is putting previously modified heads right and
it's nice easy to find horsepower, generally with a customer who is then
astonished at how slow the car really was before.
What amazes me though is that there are so many books out there that tell you
how seats should be cut (like any of David Vizards or Bill Jenkin's excellent
book on the Chevy engine) and yet the tuning industry never appear to read them
and just churn out the same old narrow seats time after time that don't work
well at all.
Jerry
My two cents worth -- There is good reason to grind seats with three
diferent angles. That allows you to control the valve contact surface on the
seat. It allows adjusting the width of the contact 'ring' of the valve on
the seat. And, it allows adjustment of where, on the valve face, it contacts
the seat.
I submit that 3 angle seat grinding is appropriate for doing a good valve
job. I submit that 3 angle seat grinding is not done for increasing flow.
That would be done by port grinding and a flow bench.
I dont see how multi angle seat grinding could hurt if you have time
and-or reason to blend the seat to match the port.
So, I think the guy who offers 5 angle valve grinding knows something
about salesmanship.
Jerry
"Thomas Hood" <thoma...@virgin.net> wrote in message
news:1712da36.02041...@posting.google.com...
AWM
"j.brew" <james....@btinternet.com> wrote in message
news:a9kor1$r7d$1...@knossos.btinternet.com...
> After a visit round Williams F1 factory I'm assured the perfect seat is
> knife edged, but the engine only lasts one race... :-)
> Jb
less prone to trapping particles than a wide seat.
Graeme
would be no further forward. Asking here is likely to get a variety of
answers and information so he can make a judgement for himself. Not usually
good practice to ask the person selling if something is worth the money.
Graeme
"Tom" <tma...@xtra.co.nz> wrote in message
news:3CBDEEF2...@xtra.co.nz...
Bob
Sone correctly a 3 angle is all that is needed on most engines
unless you are looking for performance. I have on premise a full lne
machine shop and with stock or mild upgrades we use either 3 or 5
angle cutters (all our work is done on Sunnen equipment). The high
performance work we do is done on the Sunnen machine using a profile
cutter which has 9-12 angles depending on the application. I took a
old head and did a 3 angle job then flowed it to have a base number. I
then did it with a 5 angle and there was no noticable difference in
the flow but when it was done on using the profile cutters there was
an additional 15 CFM of flow. Unless it is a high output engine a 3
angle seat is adequate. If you are going to change the cam in this
engine (or the rocker ratio) I would be more concerned about making
sure the valve stem height is set correctly and the caculations have
been done to make sure you do not get into coil bind. Hope this helps
you out.
Bob
www.partsbuddy.com
thoma...@virgin.net (Thomas Hood) wrote in message news:<1712da36.02041...@posting.google.com>...
Thomas Hood
> >Subject: Is a 5-angle valve seat better than a 3-angle?
> >From: thoma...@virgin.net (Thomas Hood)
> >Date: 17/04/02 17:47 GMT Daylight Time
> >Message-id: <1712da36.02041...@posting.google.com>
> >
> >The Cylinder Head Shop here in the UK is offering this service on
> >their Serdi equipment but I have never seen this offered before. Does
> >it flow noticably better?
>
> Nope, but it isn't really a meaningful question because the widths and angles
> of each of the cuts and the resulting throat diameter are unknowns. 3 angles
> that got these right would obviously be better than 5 that were all wrong.
>
I don't see why its not a meaningful question. I would have thought
that it could (would?) be taken as read that the 'best' angles, throat
diameter etc would be used (whatever they may be!)
Sooo... given a nice valve cutting machine and somebody who knew the
best angles to use (such as yourself) would a 5-angle cut prove
superior?
Or is it the case that like 4-valve engines proving superior to
5-valves due to other constraints, less is more?
I certainly didn't get sucked in by the advertising. I would simply
like to understand the issue a little better. Some other things
written on the site don't quite tally with what I've read in the past.
Specifically what they have to say on 2-piece exhaust valves being an
accountants choice.
Incidently I have been trying to come by a copy of Gas Flow in the IC
Engine by Annand but it appears to be out of print. Are there any
specialist 'motor sport' bookshops or otherwise where I might find a
copy.
Thanks,
Tom
Dave Baker
>From: thoma...@virgin.net (Thomas Hood)
>Date: 18/04/02 15:11 GMT Daylight Time
>Message-id: <1712da36.02041...@posting.google.com>
>
>pumar...@aol.com (Dave Baker) wrote in message
>news:<20020417143448...@mb-fj.aol.com>...
>> >Subject: Is a 5-angle valve seat better than a 3-angle?
>> >From: thoma...@virgin.net (Thomas Hood)
>> >Date: 17/04/02 17:47 GMT Daylight Time
>> >Message-id: <1712da36.02041...@posting.google.com>
>> >
>> >The Cylinder Head Shop here in the UK is offering this service on
>> >their Serdi equipment but I have never seen this offered before. Does
>> >it flow noticably better?
>>
>> Nope, but it isn't really a meaningful question because the widths and
>angles
>> of each of the cuts and the resulting throat diameter are unknowns. 3
>angles
>> that got these right would obviously be better than 5 that were all wrong.
>>
>
>I don't see why its not a meaningful question. I would have thought
>that it could (would?) be taken as read that the 'best' angles, throat
>diameter etc would be used (whatever they may be!)
If there was one thing you almost certainly couldn't take for granted that
would be it. I see 1 in 10 professionally done heads that have anything like
the right seats in them. Usually too narrow with too big a throat. Read my
website.
>Sooo... given a nice valve cutting machine and somebody who knew the
>best angles to use (such as yourself) would a 5-angle cut prove
>superior?
I doubt it - or at least the difference would be minimal and need a flowbench
to A) prove one way or the other and B) find out what the optimum widths/angles
were. Which takes any job way outside a reasonable budget.
On engines I build a lot of, like say the XR2 Challenge ones a few years ago, I
spend hours experimenting to find the optimum seat profiles - which varies with
cam lift anyway so there is no one single optimum profile. After years of
experience I'll get pretty damn close on any head now without having to use the
flowbench but for that last few % you still need to experiment.
>Or is it the case that like 4-valve engines proving superior to
>5-valves due to other constraints, less is more?
>
>I certainly didn't get sucked in by the advertising. I would simply
>like to understand the issue a little better. Some other things
>written on the site don't quite tally with what I've read in the past.
>Specifically what they have to say on 2-piece exhaust valves being an
>accountants choice.
Best way to make them in most cases which is why OE manufacturers do. How often
does a modern valve fail? Basically never.
>
>Incidently I have been trying to come by a copy of Gas Flow in the IC
>Engine by Annand but it appears to be out of print. Are there any
>specialist 'motor sport' bookshops or otherwise where I might find a
>copy.
>
>Thanks,
>
>Tom
and Roe - My copy was photocopied from a friend's copy many years ago -
although I think I lent it out and never got it back. Only 2 chapters are of
great use but they do contain excellent information although it is easy to
misinterpret and probably helpful mainly to people with a good grounding in
fluid mechanics. For real world heads rather than test bench simulations you
need to do your own flowbench research and that takes years.
All the basics are in part 1 of my cylinder head article. Follow that and
you'll be close enough on most heads. I give too bloody much away I think.
Maybe I should stop writing and preserve the mystique a bit more.
Tom
You must be hell in a supermarket!
As it happens, the post didn't mention money, price or cost..
If a surgeon said he could fix your knee with an arthroscopy,
do you wander around getting opinions from lay people rather
than question the surgeon?
To refrain from questioning the provider of a service, of any
benefit they may provide, because their opinion may be profit
motivated is burying your head in the sand!
Never bought a car off a dealer?
Peter Hill
No, a rad on the seat causes the conical jet of gas which flows though
the valve/seat gap at low lift to adhere to the seat. When it breaks
away from the seat it forms a turbulent flow which blocks the flow
though the valve/seat gap. A nice sharp edge is required to get good
separation of the flow. The initial flow though the port is critical
to accelerate the gas early, it affects the flow throughout the intake
process. Loss of that flow to turbulent conditions at the seat/valve
exit will reduce peak flow. Full radius seats went out of use before
WWII.
As for 5 cuts where do you make the extra 2 cuts?
Normal 3 cut - smaller angles are 74 Honda, larger 89 Nissan.
Throat 53/60 degree inc, Nissan exhaust 30 degrees inc.
Seat 90 degree inc
Land 105/120 degree inc.
Any cuts outside the land are of no use as it will not see the gas
flow, that hopefully separated from the port at the edge between seat
and land.
If extra cuts are in the throat, then 5 cuts are not enough. The
angle between successive changes in port wall should be less than 15
degrees included (7.5 degree change in wall angle - and smaller would
be better) to prevent early separation. So that should be.
1: 15 degree inc
2: 30 degree inc
3: 45 degree inc
4: 60 degree inc
5: 75 degree inc
6: 90 degree inc Seat.
7: 120 degree inc land.
Cuts 1-5 (or single throat cut on 3 cut port) should have a radial
width of about 1mm in total. If the radial width of all cuts in the
throat is greater than 1.5mm then.
1. Valve seat is too big for port - replace seat and fit correct
valve.
2. Hole in valve seat is too small - get it bored and ported to match.
3. Porting job is rubbish - take it back.
With a CNC grinder (or dresser for grinding stone on hard seats) it
should be possible to make a cutter such that the throat is a smooth
rad, blending into a narrow 90 degree seat with a sharp edge to the
120 degree land. It would only be of use for the one size of port so
it is cheaper to get a set of tapered cutters that fit a wide range of
port sizes.
I refuse to discuss crap French cars with 120 degree valve seats!
--
Peter Hill
Can of worms - what every fisherman wants.
Can of worms - what every PC owner gets!