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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
Comments: To: ldhamm@xmission.com, "Vanagon@VANAGON.COM" <Vanagon@VANAGON.COM>
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 http://ebyte.com/wow


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