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I never said that you dont get backpressure with a 3in. exhaust.  You will but it may not be what is necessary.

Quote (Rerun72 @ Jan. 30 2002,10:40)Actually you really do need back pressure thats exactly why our race car dropped back in the one race when the Headers fell off we were losing Power.  It is really key.  Thats the reason why you have to be sure not to have to big of an exhaust.  Trust me.
The reason your car fell back when your headers fell off is that you had no velocity in your primary tubes.  No exhaust is not always better than having an exhaust, and bigger pipes aren't always better than smaller pipes.

You need to match the air velocity so that when the exhaust port opens there is a negative pressure pulse at the valve.  Then as the air moves out of the cylinder you want it to be pulled out.  If the air is too slow then it won't happen, and if there is pressure there the exhaust air will have to be pushed out by the piston with force, which will lower the available space in the cylinder for the next intake phase.

Just remember, back pressure is bad and velocity is good.

Fine I am just gonna give up and say your right.

Back Pressure  
Final point check it out.

Hmm, hard to say that Rex is wrong, since he is using fluid dynamics and basic engine mechanics/dynamics to back his cause up... and you have some guy's opinion on a webpage? I guess some people believe everything on the Internet...

Hey you believe whoever you want but I just posted that since it explains exactly what the guy initially asked.  What exhaust should I go with.  If you wanna believe Rex fine.  But I know I am not wrong.

This is what I believe, if you are getting a turbo for sure get 3" exhaust. The turbo will make enough backpressure not to lose too much low-end power. If your going with Nitrous I would just get an exhaust cut off. That way you won’t compromise drivability.

Wouldn't this stuff all be dependent on the specific engine, the number of valves, max rpm, etc?
Like that link is talking about a 3.0 v6. That engine is much different than a quad 4..

If I stuck the exhaust from Rex's car onto my car with the 3100v6, well it probably wouldn't work so well.

your forgeting thermodynamics play a major role in this also, ecspecially over a larger span of exhaust...... HotExhaust = Higher Velocity Exhaust, Cold Exhaust = Slower Velocity Exhaust, Larger pipes allow thee Exhaust to cool down slowing it down, having a smaller pipe will keep the exhaust hot making it travel faster.

Also, when larger than needed pipes are used, there is not enough constant flow, ecspecially during low rpms, so there isn't a steady flow through the pipes, this causes turbulent flow with in the exhaust which also slows things down.

I say get a 1/2 inch pipe and give it a wirl

Thats the best advice I have heard yet.  Thanks Taz... .  Oh yeah by the way I wasn't using that necessarily cause of the Engine type just the explaination to the use of the exhaust and when you should use what size.

I definitely would agree with what Rebel said as well.

Quote (Rerun72 @ Jan. 31 2002,12:05)Back Pressure ÂÂÂ
Final point check it out.
So we have web sites to back up our ideas....

http://www.warnertechnology.com/Cars/backpressure.shtml

http://www.geocities.com/MotorCity/7177 ... heory.html

http://www.magnaflow.com/02problems.htm

http://www.burnsstainless.com/TechArtic ... heory.html

I will stand my my statement that for a Quad4 a 2.5 inch exhaust is correct for high power.  2.25 is ok for the street.

Don't worry, as short as my exhaust is the pipe never gets cold.

here's a question... would 2.25 be big enough if i got a camshaft put in?

Cause i really don't wanna have to sell my new Superturbo to buy a bigger one...

Yes, a camshaft at most is 10hp to the wheels...you don't need 2.5 or bigger unless your gonna be pushin 50hp+ than stock, and then its not even a necessity to get 3.0 unless you got like 275hp or something more.