Date: Tue, 19 May 1998 12:59:43 -0400
Reply-To: Erik O <koesel@UAKRON.EDU>
Sender: Vanagon Mailing List <Vanagon@vanagon.com>
From: Erik O <koesel@UAKRON.EDU>
Subject: Inline Exhaust Theory: part I
Content-Type: text/plain; charset=us-ascii
Finally put the finishing touches on my new exhaust system for my 82 GTI
powered Westfalia. Thanks to everyone who offered input, suggestions,
ect.
The major problem I encountered was not being able to use the "Dasher"
4-2-1 manifold I had purchased for it last fall. The manifold was simply
too tall to clear the left motor mount. After scouring through two "VW
only" boneyards and looking at at least 50 pulled 4cyl cores, I think
I've seen every exhaust manifold ever put on a inline VW. I'm sure I
could of missed a few, but have come up with only two possibilities for
use on a vanagon. The first was out of a 1.8L Golf with 10:1 compression
(86 or later). This is the one with the round outlet that uses a donut
shaped gasket and uses those stupid spring clips to hold the downpipe.
This is also sometimes referred to as the dreaded stock manifold, I'll
explain this later. The second was from an 81' Audi 4000. This was a
4-2-1 style manifold with the dual outlets. The shape of this manifold
looked like it would fit perfectly in a vanagon, nicest dual outlet
manifold I've seen (in Vanagon terms).
I choose the Golf manifold, against the recommendations of a few
listmembers, but I have my reasons....
"The Dreaded Stock Exhaust Manifold is on your car. It's design is just
about as bad as you can get... It is generally recognized that
Volkswagen had a decent manifold but they 'improved the design' to
accommodate the Lambda Sensor and screwed up the flow characteristics."
- Parts Place
Autotech, Techtonics and most all others agree with this, and they are
probably right. I've seen dyno test results that confirm it. However,
the performance gains on the lower RPM range were modest at best. Maybe
up to 2 HP from 1000 to 4500 RPM. Now don't get me wrong, I'm a HP
scrooge, I'll take any little bit this engine will give me, but I
question the reliability of these results. If these companies were
claiming 6 to 8 HP on the lower end, then I may be inclined to follow
their recommendations, but 1 or 2 HP is too close to zero to convince me
that these tests were nothing but best case Dyno results, which while
true and accurate, don't occur in most applications and testings.
Companies have commercial interests in providing the best technical test
data in evaluating their products, that's advertising and there's
nothing wrong with it. And while these 4-2-1 headers and downpipes
really help the engines breath at higher RPMs, they're just too close to
zero in my range to make me bite. Plus, I can get that low RPM power
back, if it's there at all. Read on.
Speaking of range, I think it's important to note this range issue. I
figure my range with this engine is between 0 and 5000 RPM. I normally
shift when I reach 4500 RPM or so. I sometimes leave it in second or
third and wind it out a bit, reaching higher RPMs.
While this isn't necessarily bad on these engines and they seem to like
it, there are just reasons to keep your foot off it a bit. One of my
major concerns is the higher RPM's effect on my 82' air-cooled Vanagon
transmission. These trannys were NOT designed for the RPM range of the
water-cooled inline engines. What's the redline for a 2.0L air-cooled?
4400? My GTI engine redlines at 6500, I think. Therefore, my engine
might last all day at 6000, but I hate to think what that's doing to the
transmission. Vanagon transmissions have never been considered to be
that reliable and bulletproof anyway. Like barbecuing, "low and slow".
Another thing I questioned was the comment about VW "screwing up the
flow characteristics". I happen to have a lot of confidence in VW
engineering, so what could they have done to these stock manifolds that
would have made them such lousy performers? (I'm not talking about high
end here. A Bored out 4-2-1 or a tubular header will almost always help
high RPM breathing.) In looking at my Golf manifold, the flow looked
pretty good. Nice sized ports with gradual merges into a decent sized
outlet. WAIT! What the heck is this thing blocking the outlet. The
Oxygen sensor? Ahh, that might be what these companies are talking
about. VW messed up the flow when they added the O2 sensor to American
destined markets. The O2 sensor sticks down in the outlet and is about
1/2 by 3/4 of an inch in size. My understanding of exhaust flow theory
tells me this is a bad idea, at all RPMS. Taking that bugger out and
replacing it with a 5 buck plug might have just got me that extra couple
HP or grunt that I was missing from those header dyno tests. The only
way to confirm this is to do Dyno testing of my own, no way! I test my
van on the highway.
End of part I
_______________________
Erik O Akron, Oh
82 GTI Westfalia
http://ebyte.com/gl
http://ebyte.com/wow
| 
