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View Full Version : What is the best size for exhaust pipe?



Ren96240SE
10-17-2000, 06:45 AM
I'm looking at a Cat-back system that comes in 2" pipe dual 2" exhaust and 2 1/4" pipe dual 2" exhaust. I want to make sure I keep optimum back pressure so which is the best for performance of a NA car with minor upgrades. Also taking into account next stage is greddy header & hiflow cat, then possibly upping to ~10-1 pistons and total seal rings with a port and polish and JWT ECU. (life starts looking up when your neighbor is a mechanic who builds and races as a hobby! Suddenly you have access to more options for less $$$) My goal is not to build a V8 stomping turbo monster (even though they're cool as hell!!!) but a ~200hp NA car with quick throttle response (most important in my opinion) that is even more fun to drive.

240fan
10-17-2000, 07:33 AM
thats what I want to build, a ported n polished NA car. sorry dont know if your setup is for optimum back pressure.

10-17-2000, 11:20 PM
Ok, so first of all, its not backpressure that you need for optimum NA performance, its exhaust gas velocity. Smaller pipes, which are better for gas velocity, also have higher backpressure, which is where the confusion comes from.

Now, what you want is maximum exhaust velocity and minimum backpressure -- note that these two are often mutually exclusive. 2" is good for exhaust velocity at low RPM's, but is excessively restrictive at high RPM's. 2.25" is ideal for mildly-tuned NA 240sx's. If you plan to do modifications to increase the engine's volumetric efficiency (like the header and the p&p job), then you may want to think about even going to a 2.5" pipe. You may lose a little low end due to the low gas velocity, but the low backpressure will be more important at high RPM's, and will allow you to make the most of your planned mods.

Asad

<BLOCKQUOTE><font size="1" face="Verdana, Arial[/img]quote:</font><HR>Originally posted by Ren96240SE:
I'm looking at a Cat-back system that comes in 2" pipe dual 2" exhaust and 2 1/4" pipe dual 2" exhaust. I want to make sure I keep optimum back pressure so which is the best for performance of a NA car with minor upgrades. Also taking into account next stage is greddy header & hiflow cat, then possibly upping to ~10-1 pistons and total seal rings with a port and polish and JWT ECU. (life starts looking up when your neighbor is a mechanic who builds and races as a hobby! Suddenly you have access to more options for less $$$) My goal is not to build a V8 stomping turbo monster (even though they're cool as hell!!!) but a ~200hp NA car with quick throttle response (most important in my opinion) that is even more fun to drive.<HR></BLOCKQUOTE>

**DONOTDELETE**
10-22-2000, 08:27 PM
i agree with asad... but if ur gonna go high compression, go with 10.5:1 and hotshot headers. also if you can deal with the emissions, get don nimis dump pipe instead of a high flow cat...

steve