I'm going to get a custom cat-back made because it seems like the best way to go vs. buying a Stillen, Warpspeed, OBX, etc. I want a fairly quiet exhaust with NO DRONING, that still flows better than the stock one. I am planning on putting in at least one resonator and a 5th gen muffler at the end.

So the questions are:

Mandrel-bent vs. Pressure-bent
Clearly mandrel bent is better, but how much better? This may be hard to quantify, but is it worth ~$260 for mandrel-bent vs. ~$150 for non-mandrel bent? My general thinking is that if I'm going to do this, I may as well do it right and get the mandrel-bent. But if it's only going to scavenge like 1hp, then it may not be worth the extra $110.

5th Gen Muffler
I hear great things about the 5th gen muffler, in that it flows well but is still relatively quiet. However I also read that the opening is 2.25", like the stock exhaust. If the cat-back is 2.5", what do I do? I think I recall someone boring out the opening on the muffler to accept a 2.5" pipe, but I can't seem to find the post.


Anyone have any feedback?

 

I was at Warpspeed awhile back and Dallas was showing me the difference between their pressure bends and their mandrel bends and there was hardly any difference. Mandrel is the same no matter what but I 've seen pressure/crush bend quality vary from shop to shop.If the place you're getting your piping from does good pressure bends, it's probably not worth it to pay more for mandrel IMO.

Warpspeed can also change the inlet to a 2.5". I'd give them a call and talk to Dallas about it.

 

Yeah, just about any exhaust shop would be able to open the inlet of a muffler to a larger diameter, its really no big deal. If you want some gains and don't really care too much about the environment, you could get a straight pipe with the money you saved going with crush bent pipes.

 

I've got a 5th gen muffler (2001) that has had its inlet pipe swapped from 2.25" to 2.5" dia. I bought it from Jime (fellow org'er who did 12.6 sec 1/4ET). I believe the original pipe was removed, a bigger hole was cut out and then a new 2.5" pipe welded in place.

(BTW, the pic in my sig is outdated in case you're wondering why the muffler has only one tip & not two)

 

Okay, I'll check out their mandrel bends and see just how much I'd be losing.

Good to know about the muffler. As for the straight pipe, I actually converted my POS rattling RT cat into a "straight cat".

 

I don't quite understand why changing the stock 2.25" pipe to a 2.5" pipe would be any different because the internal pipes in the muffler are still 2.25". I'll also add that running a slightly tapered exhaust, larger at the front to slightly smaller at the muffler, actually improves exhaust flow by keeping the exhaust hot as it travels down the pipe. I'm not talking about tapering from a 3" pipe to a 1.5" pipe is good, but going from 2.5" to 2.25" is completely fine and actually better than a full 2.5". Tapering the exhasut done slightly is a well known exhaust design.


Dave

 

Good point Dave. To be honest I really didn't think about it all that much, I just remembered hearing about someone else do this, so I figured...

 

Hmm thats good to know. I always wondered if having a budget y-pipe (which is 2.5" diameter") and then keeping that stock cat and adding an Apexi WS catback (which are both 2.25" diameter) would have any negative effect on performance rather than just getting everything 2.5" diameter. But after reading that i guess not, and may even be better.