1641cc a lousy engine combination?
John Hirsh
*************************************
"The 1641 P&Cs are a straight swap for the 1600 P&Cs but they are very thin
walled and often have a very short life - 20,000 miles if you are lucky,
according to folks I have spoken too. They also have a very thin sealing lip
at the top of the cylinders, so it's much easier to get a leak developing
there and ruin the head. The 1641s increase the compression ratio a little -
from about 7.5:1 to about 7.8:1 which would probably need premium unleaded
to avoid detonation, or else thin spacers under the cylinders to increase
the head space to get the compression back to 7.5:1 so you can use normal
unleaded fuel (91 RON Octane).
1776 P&Cs require machining of the case and heads to fit the larger bore.
They have normal thickness cylinder walls, so they won't distort like 1641s
and will last about as long as 1600 P&Cs.
The head space is still a problem and using standard 1600 heads (fly cut to
fit the larger cylinders of course) and will result in a compression ratio
of about 8.4:1 which is probably a little too high even for premium unleaded
(95 RON octane).
So you'd need the heads machined for a larger head space and/or spacers
under the cylinders. But you can't go much past about 0.9mm spacers before
the push rods become too short and the rocker arm angle on the valves
becomes too steep, so you need to consider longer pushrods too. And with
spacers under the cylinders, the exhaust ports are further apart so fitting
muffler systems can be a problem.
1641s MIGHT last OK in an engine which has mild use ( not subjected to the
high temps of regular hard driving), but if you have more power, you're
likely to use it right???
You only have to look at the history of the VW engine design - the 1200s
have very thick cylinder walls and almost never leak at the head joint (77mm
cylinders). 1300s ditto (77mm cylinders but loner stroke of course). The
1500 (83mm cylinders) has thinner walls (larger inside diameter with
itentical outer diameter) but doesn't seem to suffer head sealing problems
either.
The 1600s (85.5mm cylinders) have thinner walls again (still the same outer
diameter) and DO occasionally have head sealing problems...VW never used
walls thinner than this, and that tells you something significant in itself.
So the general rule is "machine-in" P&Cs are likely to last longer than
"slip-in" cylinders, no matter what the capacity.
Add to that... the 57cc extra capacity of the 1641s will give you a very
small increase in power (until the cylinder start to wear/warp/leak), but
the 192 extra cc of the 1776 will make a noticable difference, and will last
about as long as stock 1600 P&Cs. And if you want a "cheap" increase in HP,
the 1776 CAN just cope with the standard 34PICT/3 carby and inlet system,
but can easily be upgraded again with twin carbs etc when money allows, yet
you'll FEEL the difference in the increased capacity even with the stock
inlet system and single carb.
Rob
Rob and Dave's aircooled VW pages
Repairs and Maintenance for the home mechanic
http://www.geocities.com/aussiebug1970/
**********************************************
I didn't realize the 1641cc engine is that crap.
Any comments on Rob's article?
Vanagon Man
compression ratio to 7.0 to one or so so that there is no problem with pump
gas.
--
Adam P
81 Westy "The Brick "
70 Single Cab "Whitey"
74 Beetle "Ol Yeller"
73 Transporter (STILL at paint shop)
1988 Vanagon Wolfsburg
75 Campmobile "for sale'
Used Vanagon Parts for sale (mostly aircooled)
"John Hirsh" <nospam_s...@yahoo.com> wrote in message
news:Kd589.11099$7V6....@news-server.bigpond.net.au...
John Stafford
"Vanagon Man" <vgo...@msn.com> wrote in message
news:ajqs0k$1dirfq$1...@ID-149037.news.dfncis.de...
> I guess these folks never thought of shimming the cylinders to lower the
> compression ratio to 7.0 to one or so so that there is no problem with
pump
> gas.
There's no problem with pump gas if the engine is timed properly. Lowering
compression to 7:1 simply lowers its efficiency, diminishes mileage, and
oddly can also cause more heat (the timing thing again.) Bad idea, IMHO.
John Willis
scribbled this interesting note:
>I guess these folks never thought of shimming the cylinders to lower the
>compression ratio to 7.0 to one or so so that there is no problem with pump
>gas.
I quote from the article:
>> So you'd need the heads machined for a larger head space and/or spacers
>> under the cylinders. But you can't go much past about 0.9mm spacers before
>> the push rods become too short and the rocker arm angle on the valves
>> becomes too steep, so you need to consider longer pushrods too. And with
>> spacers under the cylinders, the exhaust ports are further apart so fitting
>> muffler systems can be a problem.
--
John Willis
Rob
And Adam, if you actually read your own clip of that post, you'll
about half way down "thin spacers under the cylinders" and the bottom
line talking about "0.9mm spacers", so yes - us folks DO know about
using shims!
And if you knew any more about the post, you'd see that I was talking
about using 91 RON octane (87AKI in the USA) unleaded which works well
with 7.5:1 compression (no oxygnates in Aussie fuels to stuff them
up).
You'll also note that in every one of my posts I am careful to qualify
things I say, like "91 RON octane", rather than just "91 octane" as,
unlike some people, I am fully concious of the worldwide audience we
have in these newsgroups, and the differences in terminoligy and such
which exists. So even though John Hirsh lifted that post from an
Aussie VW newsgroup, it will still make sense to folks in the US if
they care to read it right.
Regards
Rob
Rob and Dave's aircooled VW pages
Repairs and maintenance for the home mechanic
http://www.geocities.com/aussiebug1970/
"Vanagon Man" <vgo...@msn.com> wrote in message news:<ajqs0k$1dirfq$1...@ID-149037.news.dfncis.de>...
Rob
I didn't say that 1641s were crap. I just said that they had potential
problems and was trying to make folks aware before they jumped on the
"quick and easy" route for getting more grunt from their engines.
I think I was reasonably fair on the 1641s myself, since I also
pointed out a few of the problems of the 1776 (which the 1641s were
being compared to) as well.
Comments from others are most welcome of course.
Regards
Rob
Rob and Dave's aircooled VW pages
Repairs and maintenance for the home mechanic
http://www.geocities.com/aussiebug1970/
"John Hirsh" <nospam_s...@yahoo.com> wrote in message news:<Kd589.11099$7V6....@news-server.bigpond.net.au>...
> small increase in power (until the cylinders start to wear/warp/leak), but
Jan Andersson
John's got it right. The CR needs to be in the CORRECT value range, not
"low enough so it'e definitely safe"
Jan