exhaust sizes?

[slideways_ninja]

ive seen a lot of people recommend a 2.25" exhaust for the 4 cyl. hardbodies like my own why is that?

[seang]

Hi, I'm running a 2 1/8 inch catback straightpipe on my ka24e. It has 134 hp even still, so the stock computer tune is why. However, it does seem to rev a little more freely near redline which is essential every time I get on the highway. Its a little boomy without a resonator or muffler. I wish I would have went with just a 2 inch instead because I think that is plenty unless your actually doing a nismo cam and time consuming tuning of the ecu, among other mods. The bigger the pipe, the louder it will be. A 3 inch on a stock truck 4 banger would be ridiculous. I do think a straightpipe sounds better than a fartcan, and a flowmaster isn't a good idea on a 4 banger, just my opinion.

[PEZi]

main reason is back pressure... the non turbo 4 cyl engines need backpressure so you for sure don't want to go over 2.5 without a turbo... 2.25 is generally the best choice for the torque to hp balance

[Desert Rat]

Exactly. You need some backpressure to make torque, and truck engines need a little grunt to them.

[seang]

Today, my 2 1/8 inch flexpipe tailpipe (catback straightpipe), finally rusted through after 3 months. I put on a 1 7/8 straightpipe from the cat back. I noticed a torque drop near redline, but around 4000 rpm, it is a little punchier. HP seems about the same at 134, but it doesn't carry up to 6200 rpm like it did with the 2 1/8, more like 5450 rpm. This is a DD, so I'm keeping the smaller one. For performance duty though, go with a 2 1/8 or 2 1/2. Speaking for the truck version of the ka24e, z24 engine similar.