Somebody help me out here. What size are the Rotary Perfomance and N-Tech high-flow cats? If they are 3-inch pieces, and most downpipes are 3-inch pieces, what good is it to have a 3 and 3/4-inch cat-back exhaust like the Jap-spec Greddy or A'pexi GT? Are their advantages in that they feature straighter piping and almost straight-through muffler design rather than their pipe diameter? I'm not trying to trash anyone's exhaust. I'm just trying to make an informed decision regarding performance and sound without buying into any hype or trend.

 

The Bones and Ntech are both 3" hi-flo's, and yes you do make a valid point. As for the exhausts you mentioned, the Apexi' GT is 3" and gradually opens to 3.74"...whereas the GReddy Jspec starts at 3.71" and remains that way.

So what's the adavantage? Well, not too much with a fairly stock seven. Most of the people that get these larger diameter exhausts plan on doing heavy modifying and even going single turbo or hi-flow twins. If you look, you'll notice a lot of people run the RB and Pettit cat-backs whcih are fairly similar to stock in design and a lot run the Apexi' dual. I think that 3" is plenty for an RX7 until you get to the 'big' mods. I went with the GReddy Jspec because I plan on upgrading to ball bearing twins next year. I was just thinking ahead.

Like I said, on a fairly modded car the difference between one of these monster exhaust and a more typical one would be marginal, if any at all. However, one place where you will get hurt having a large diameter exhaust is when you decide to go with a midpipe. When you have that huge exhaust with no convertors and just straight pipe, there will be absolutely no restriction and those turbo's will just spool away and you won't be able to control them.

Until you start adding the horsepower, one of the 'monster' exhaust won't be needed....

 

yep...