Greg PAW

I'd like to get the best exhaust available. My focus is maximum performance. I'm not really concerned about sound or loudness or emission (no cats is an option, I'll send the arbor day foundation some money to rid me of environmental guilt). I just want the best flowing exhaust I can get.

I'd like to increase the power on the higher end as I plan to have the engine running higher revs within the next year or two. Gas velocity is also important though. I'm thinking in the area 2.5" pipes but please tell me what you guys think.

All comments welcome!

fanta4

this topic has been beaten to death. i dont think there is a "best" exhaust. it seems that everybody has their own preferences here.

JWG

for maxiumum performance, you would need an exhaust with approximately 14 "inches of water" backpressure.

Audi's OEM 2.8 exhuast has approximately 24 inches of water backpressure.

Anything less than 14 inches of water in the low 200 hp range and you will degrade performance.

For example, a 4000 hp dragster requires no backpressure;a 850 hp NASCAR engine runs 4-6 inches of water.

So, as you increase HP, you may decrease backpressure. As you increase to 300 hp, 12 inches will likely prove optimal; 400 hp and 10 inches will likely prove optimal.

So, you should find a mechanic/engineer/designer from a race team who knows about exhaust backpressures and ask him to design a system for you. Alternatively, you could learn how to measure backpressure yourself and tackle the problem by trial and error, until you get optimal measurements.

Note: This does not apply to turbo charged engines where the turbo itself creates and controls a majority of the backpressure.

PitViper

How do you ensure you have the proper backpressure? Does this sound proper? a Y 2.25" to 2.50" from the cats, through 2.5" pipe to 2.5" in/out resonator to a muffler with 2.50" inlet and dual rear 2.25" outlets?

How do I measure backpressure?

JWG

I only know the theory and numbers from my research into the optimal backpressure for the 12v; I lack practical experience in these matters. However, any competent exhaust speciality shop should have the ability to measure backpressure.

As the measuring standard indicates, you obviously use the pressure from the exhaust system to push water up and down a tube with a scale marked upon it.

I bet an intelligently worded Google search will get you to a web site that will provide you instructions on how to make a home-made backpressure scale and measure the exhaust system.

I feel pretty sure that it does not require a supercomputer and a degree in rocketry--any one of us who can do basic car repair should have the means to do it with some basic instructions.

PitViper

thx

MikTip

Look at systems other Audi types have custom fabricated! ;O)

Especially a system, where that person has gone through all the trial & error of various pipes, bends & mufflers, to arrive at a "good" system! ;O)

Example: UrS4's custom setup.

Or:<ul><li><a href="http://home.ec.rr.com/miktip/page2.htm">http://home.ec.rr.com/miktip/page2.htm</a</li></ul>

snowman '92 100

<a href="http://autorepair.about.com/cs/troubleshooting/a/aa112401a.htm">http://autorepair.about.com/cs/troubleshooting/a/aa112401a.htm</a>

"Starting with the engine at idle, slowly increase engine speed to 3,000 RPM, engine vacuum should be equal to or higher than idle vacuum at 3,000 RPM. If vacuum decreases at higher engine RPM's, an excessive exhaust back pressure is probably present."

Bryans12v

To convert inches of water to a pound measurement?

Then you would be able to use a flowbench.

Hokie - STI avant

I went through a few setups and eventually modeled mine after MikTips. It performs and sounds great.

Eventually I plan to go with UrS4's single cat setup.

Mike