A 2-1/2" system is adequate for most street cars, and 3" exhaust pipes might help slightly when you begin to run in the mid 12's. Faster cars definitely benefit from 3" exhaust pipes. In addition to width, the actual design of the exhaust pipe has a tremendous effect on performance. The more bends, kinks, and rough edges inside the pipe, the greater the internal friction on the exhaust gasses and the less efficient the exhaust system. Therefore, performance exhaust systems usually feature exhaust pipes that are smoothly bent, smooth on the inside, and have as fewest bends as possible to reduce the friction inside the pipe. Uniform diameter head-pipes of adequate size will improve performance over carelessly bent or badly crimped pipes. Mandrel bent pipes provide the best available performance. So, if it was mine, I would seriously consider the 2 1/2 inch pipes over the 2 1/4. The less back pressure you have, the more efficient the engine. Well designed exhaust systems will actually draw the gasses out instead of creating back pressure. Now, also consider going with a header that will work to help the exhaust system draw out the gases. A stock cast iron manifold creates too many bends and turns, therefore less efficiency.

 

Remember folks you do need SOME back pressure. That is why you do not want to go larger than 2.5. If you goa 3 on these cars, you will actually loose HP. The reason why is on the intake stroke there is usally some overlap between exhaust and intake. If you do not have the right amount of back pressure, you will suck some of the exhaust into the intake cylinder which obviously hurts HP.

 

Yeah, but that is unlikely with a stock exhaust manifold. Hell, even with a tuned header, you are still going to get some back pressure unless you run it wide open right out of the head. Old racers opened up their manifolds exhaust systems with a cut-out for years, because it created a better flow, therefore more horsepower. Look at the funny cars. Right out the top from the header.

 

I know not to go too far. I've heard all about it. Some dumb*** with a civic, wanted to put 3 in exhaust on his car. The other guy told him that little 4 banger wouldn't run with it. Anyways. I just wanted to know if going to 2.25 was too much.

 

No Charles, the 2.25 will work just fine with your set-up.

 

Yes, I know now GLen. Do you think i could install the exhaust myself?

 

My exhuast is all clamped on. When i get my headers in a week i am going to see if i can keep this setup.

 

I dont see whats wrong with the exhaust being clamped on. Welded exhausts can leak too. BELIEVE ME I KNOW.

 

mine looks sound. I do have a leak, but at the gaskets.

 

I have the adapters and all. I believe i can clamp them together without leaking. If you use the adaptors right, it shouldn't leak at all.