2.5 to 3.0 Exhaust

AJ/FormS said
^^ what he said^^
back pressure isn't even good for lawnmowers.

:rofl:

d1970 said
I guess back pressure is not the right word to use. With the larger 3 inch pipe compared to the 2.5 pipe you are going to lose some savaging, you will have more exhaust turbulence happening at low rpms which slows down the exhaust flow, which will effect the low end torque. At higher rpms there is no problem with the exhaust flow and the 3 inch exhaust will work better if your motor is tuned properly. Smaller diameter pipes will usually produce better low- to mid-rpm torque. Larger diameter pipes usually produce more mid- to high-rpm torque."

Most of the scavenger effects are in the header.
Then comes the collector. If it is he wrong size and shape, there is a power loss. Then it is the length of pipe of the collector. It should be the same size for as long as it produces torque. To much or not enough will hurt power. If you incorporate a pressure termination box, the pipe size should remain the same afterwards. In some cases, going down a size doesn’t hurt but in some cases, it may add or loss no power in where the pipe size after the termination box outlets. (Pipe into the muffler.)

I can’t say for certain in this case since it would have to be dyno tested to know exactly what the engine likes and his particular build is void of any specs given.

This makes your as written statement a blanket one. Following your advice, as written could be more of a mistake than an era on the side of caution for what may be or not. I have used 1-3/4 tube headers on a low compression 318 and gained power very noticeably.

The one draw back for certain is the exhaust will be louder!
Until I have engine and vehicle build specs, as well as what exactly he is doing, I’ll agree that a 2-1/2 exhaust is probably dead on the money for what he is probably doing.
:thumbsup: