I have been reading about how load a 4" exhaust is, I just woundered if anyone has run a 4" DP" to a 4" inlet on a cat ( I must have a cat) to a 3" cat back? Would this choke off the exhaust, or would that be a happy medium between back pressure and noise? Just a thought, hopefully a veteran can shed some light on this subject,

 

i've heard a FD with a 3" downpipe and 4"exhaust. loud as hell. 3" is loud to. whats are your plans for the car?

 

Check out RX7NUT13B

He has a 4" exhaust that splits after the downpipe into two cats

 

I was think 4" dp, cat then 3 " catback specifically.

 

3 inch is plenty for most sane power levels on a street car... what are your goals?

 

Its more aid in spool up, then meeting a hp goal.

 

on my old setup, i ran a T88-34D w/ a 4" downpipe... at the time, the only cats I could find were through http://www.drgas.com

I didn't need the oval piping but a 4" cat wasn't easy to locate... I didn't end up using a cat on my exhaust setup.

 

Yeah, I ran a 3 inch DP to a 3 inch to 4 inch custom made flange. From there all the way back with a 4 inch flex tubing used for coupling exhaust from electrical generators.

It was pretty looking, but was loud as hell, boosted and accelerated much faster than the 3 inch system I'm currently running. After my rebuilt engine was installed, I couldn't control the runaway boost, needed to choke it down after the DP.

Maybe you need to modify your Cat to 4 inch? I removed all Cats and run it straight through!

 

I have a magnaflow ti cat back. I can get a random technologies high flow cat with a 4" in and 3 " out. A spec kits are available with a 4 " dp. That was my plan. Not to choke the car from the turbo back, yet keep the tone resonable.

 

your exhaust can only flow as well as its most narrow point.