Date: Wed, 20 May 1998 12:08:05 -0400
Reply-To: Erik O <koesel@UAKRON.EDU>
Sender: Vanagon Mailing List <Vanagon@vanagon.com>
From: Erik O <koesel@UAKRON.EDU>
Subject: Re: Inline Exhaust Theory: part I
Content-Type: text/plain; charset=us-ascii
Larry Hamm wrote:
> Erik,
> Thanks for the progress report and the legwork that I thought I was
> going to have to do! I'm starting a diesel-to-gas swap next week, and am
> glad to have the results of your research. I'm curious about the Audi
> manifold-do you feel it's a sure fit? Do you recall where the outlet is?
> I think your reasons for going with the Golf are sound, but are there
> any other reasons you didn't use the Audi? Thanks for the input!
> Larry
The Audi manifold looked like a great fit. The best fit out of all the
4-2-1 manifolds I've seen. I've been told there are others, Fox, Dasher,
but none of those I checked looked like they had any chance of fitting
without modifying the engine mount. I am under the impression that there
are varying heights of these same manifolds that are a bit shorter and
will work. I just saw nothing personally in the last two models that
will fit. The outlets on the Audi are on the far left.
I didn't use the Audi because I don't think it's necessary. When you go
from a Gulf style manifold to any 4-2-1 setup you are essentially
doubling the volume of pipe from the head to the single collector. The
high performance parts companies would like you to think that this is a
good idea, and in some ways it is. You will see in increase in high end
HP, you are allowing more air to exit the head with those setups. These
companies are also the only ones I've known of to conduct Dyno testing
through out the entire RPM range on these setups. These Dyno tests show
an increase in horse power and torque through out the RPM range, however
the gains in the lower end aren't that significant. So it makes sense to
a lot of watercooled owners to use these tubular headers or dual
downpipe setups, because it's free HP and torque. I have some problems
with all of this....
1> Being a wise consumer, I know that companies don't post their worst
results from testing their products. Some even lie. Like the companies
that make those cheapo air compressors, with pressures up to 1200psi.
You've seen them. Since there isn't really much of a standard within the
industry defining the procedure for testing those products, for
advertising purposes, companies have the freedom of using "padded"
figures. Now, I have a lot of faith in the companies that make products
for our Volkswagens, I just think that they are going to use the best
figures they can produce, even if they aren't consistent with real world
situations. This may influence the results.
2> I also don't believe these dyno results because they are basically
saying that the VW engineers were off a bit on their designs. Off ALOT!
VW was half way, 50% of the way to producing the best manifold for their
cars. I just don't buy it. I will agree that VW screwed up in
positioning the O2 sensor right in the middle of a critical flow area of
the "dreaded" manifolds. I will also concede that VW didn't design their
manifolds for optimum performance over 5500 RPM. That's a rough
neighborhood I don't like to drive in anyway. But the same companies
that are producing these "official" performance tests are using 2X or
more pipe before the collector than VW's engineers thought was
necessary. Hummm....this may influence the results
3> In order to make a properly "tuned header, pipe is connected to the
exhaust ports of the head and a line is drawn inside with a crayon that
has very specific burning qualities. The engine is started and brought
up to temp. The crayon line will burn up to a certain distance from the
head and stop abruptly, this is an indication of a lower temp area. The
pipes are then cut at this burn mark and welded into a collector. This
makes a tuned header for that specific engine. Another way to discredit
the dyno tests is to look at the products these companies are selling.
They only make one header or dual downpipe for each bodystyle. For all
A1 chassis cars Autotech sells a tri-Y header that fits every engine,
cam, head gasket thickness, compression configuration you can put in an
inline. That's not a real tuned header or downpipe. What are these
headers doing to the low end grunt on the less than optimum setup. This
may influence the results.
All of the above is how I "convince" myself that there are no low end
benefits for opening up my manifold. I could care less about high end or
horsepower, torque rules. I'm using a manifold that's suited to the
specifications of my engine. I have a 86 GTI engine and am using a
manifold from an 87 Golf GL. They have identical compression, bore and
stroke. All I'm trying to accomplish is the most torque in the flattest
curve possible. I may even reduce my 2" exhaust before it reaches the
muffler to 1 3/4. That won't suffocate the engine and may help the
bottom end. If I need to grind a mil or two from the inside diameter of
the manifold, I will do that. That's pleanty.
Does all this really matter? Nope! I'm just an idiot who did a lot more
talking than working on this project. I just want to produce the most
efficient set up for this van. I have a goal for MPG and I'll let
everyone know when I attain it. As for driveability right now, I went
out yesterday to buy some sand for a pool I'm assembling, 35 50lb bags
in the back and it was hardly like it was even there. The van still
zooms around and pops wheelies like before. Even with a 1750lb load the
van was driveable.... and fun!
As for what manifold to choose Larry, it's probably really not that
important. The Golf I'm using is probably not the same one everyone else
is thinking of. There really is something different about it in terms of
shape and flow. We'll just have to wait for the pics. The Audi 4000
really is a slick dual output manifold and if you go this route, lets
get together sometime and race!
--
_______________________
Erik O Akron, Oh
82 GTI Westfalia
http://ebyte.com/gl
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