2.5 or 3" exhaust system??

[1 tuff z]

does anyone have any insight as to the best system for my z? i have; f54 block, p90 head w/isky cam, msa header, jcr supercharger setup. i am considering either 2.5 or 3" from the header back. i don't know if the 3" would provide too little back pressure or not.

 

david

[Brad-ManQ45]

For what it is worth, I believe you would be much happier w/a mandrel bent 2.5". Definitely quieter (less droning) and weigh less.

 

N/A engines DO like a little backpressure as compared to Turbos (which don't like ANY). Supercharged engines act about the same as N/A except are generally happier w/a bit more exhaust.

 

For exhaust discussion purposes, I will lump the N/A and supercharged engines together and turbos in their own world.

 

A lot of people I have talked to and heard from for N/A z's recommend 2.25" to eliminate droning at certain rpms (I have a '75 that has header w/2.5" and it DOES drone - this will be rectified when I swap in the V-8 and hopefully - turbo it), so 2.5" would probably be fine for you.

 

The nice part is - these can be had fairly inexpensively to bolt in from MSA/others, or have it done at a GOOD shop in your area.

 

Of course I am assuming that you are not going to be running super high boost (no intercooler) and nitrous. If this is a weekend toy then you may want to go bigger but I personally wouldn't.

 

I had a 2.5" w/Flowmaster on my '83 ZXT and hated it drone at idle and below 2500 rpm and not much better on the highway. Went to a 3" stainless mandrel bent system w/straight through oval Ultraflow and not only quieter, builds boost faster and has better top end. Remember though that this is a turbo, so you start out quieter.

 

I have a pet theory about the cancellation type mufflers and turbos - I don't think they work as well at quieting, because the exhaust pulses are a bit dampened/stretched, so there is a disparity between the affect on exhaust noise reduction between N/A and turbos that tend to favor them for N/A cars. If there is in fact a scavenging effect to the Flowmaster type mufflers, the dampened pulses from the turbo would tend to support my pet theory, and at least one magazine article I can remember did a muffler comparison on a turbo car and the Flowmaster did not do as well as the same I/O Dynomax of approximately the same size (noise or acceleration).

 

Since I went up from 2.5" to 3", acceleration times comparisons would be unfair. But the overall enjoyment of the car cannot be stated enough. Instead of the hollow droning at all times around town, you get the sound like came out of stock Musclecars when I was a teen (late 60's early 70's) and no,my memory is not shot - I had my 72 351CJ Mustang (BOUGHT IN '74) until a few years ago (when I bought it my girlfriend's mother said it was the first car a boyfriend had that sounded just right - quietly powerful)!

 

OK, I'm off my soapbox now

 

Brad