I'm going to get true duals for my car, but I'm undecided with the 2.5 or 3". The mufflers are going to be the same thickness either way, magnaflow 4x9's, and the area of a single 3" exhaust pipe is 22.1, while dual 2.5" pipes are 30.8", but then there is the increased surface area so they might not have that big of an advantave over a catback. I'm going to be around 400rwhp too since I know that makes a difference. Should I just go with 3" true duals?

 

You should be fine with 2 1/2". That being said, if you plan to go beyond 400, then you may want to consider the 3". Remember too, if you lower the car, you don't want the pipes scraping. You going dumped or all the way out?

 

Dumped, but won't the mufflers be the lowest point of the exhuast? The 2.5" and 3" mufflers are the same thickness. And I might add a 100 shot on it in the future....

 

I run 2.5's and it is great! 420rwhp.

 

I had 3" duals on my lt1 and scraped everywhere (not really that big of a deal as long as you slowly scrape and dont hit the bump hard) Im going with 2.5" duals this time around.

check out a pair of sweet thunder chambered mufflers. I had 3" dia and 18" length and loved the sound.

 

I went with 3" on my camaro because I know how the mod bug works and I didnt want to redo it later

 

I have been thinking about doing the same thing later down the road when I get more cash. I want it customized to the bottom of the car and out the back with the best clearance. I have the CME exhaust on my Camaro - what is the inlet of those pipes? I thought I might like to keep the SLP muffler that came with that option so that it wouldn't get so loud as to attract the police, but still sound nice. So I see that 2.5" piping is good for 400-420rwhp mark, but what about my current muffler?

 

Yep, I would think ahead and go 3". I sure wish I had of. If your having a set custom built, you should also consider an H-pipe set up for aftermarket torque arm and driveshaft loop clearance.

A local shop maybe able to do a nice set for close to the price of the cookie cutter duals on the market.

 

Check out the sticky in this forum about induction and exhuast mods, you'll want to read posts 6 and 13 onwards (there's a link to the sticky in my sig ).

Other things to consider are if you do eventually go over the axle, 2.5" will be much easier to locate. Also if you ever plan on a body mounted torque arm make sure you design your system with it in mind (or preferably with the ta actually fitted first).

 

dont mean to hijack the thread..but, couldnt you have the shop build the system so that you could remove the center of the system to add a TA later on down the road...like have flanges not only at the header..but also like near the rear end..so you could just unbolt and remove to get to the drive shaft, and TA location??
just thinking..

 

well that's fine, but once you remove the exhuast and install the ta where do you put the exhuast, there's not enough room for both if you mount the X or H pipe where most people normally do.

The only sucessful setup I've seen is where the X pipe is offset to one side and goes over the lower hanging bracket of the ta, but you'd need the ta there to work round it as it looked very very tight.

 

true true, ok well under what conditions would i need a TA???? i plan on going well past 400rwhp in the future....what do you think...

by the way...im going to go 3" this week on my system..i figure that i want the most flow when i get my heads and cam, abd i woudl HATE to have to change to a bigger exhaust system...
just my $0.02

 

Well following David Vizard's theory that 2.2cfm per 1hp is required 2.5" duals should be good for zero flow restriction on a 500bhp motor (~440-450rwhp), however if you had 550-600bhp the exhuast wouldn't suddenly loose hundreds of bhp. Yes there might be a restriction but I doubt it would be by much. If every single pony is required the 3" may be the better bet when you're at 600+rwhp for a noticable difference.

As for the torque arm, well a good chassis/suspension setup including a body mounted torque arm could well be worth quite a few tenths at the 1/4 mile. Power is nothing without control.

Also a body mounted ta will remove the slop/movement present with a tranny mounted one. Following Newton's laws of physics, for every action there is an equal and opposrit reaction.

This means as you accelarate away from the line the tyres push against the tarmac, and the tarmac effectivily pushes back agains the wheels which is what propels the car forward. Know some of that energy will be lost in deformation of the tyres, compression of the suspension and the rest will be channelled thru the car via the torque arm. A tranny mounted torque arm will then move as the tranny is essentially floating (it uses rubber bushes) a body mounted one won't and will allow more or the potential energy to be used to propel the car forward making it faster accelarating (traction permitting).

Take a look at this picture of a body mounted torque arm, as you can see there is barely enough room for a 3" Y collector and I-pipe. In order to get an X-pipe in there will require some careful design.



What you'd need to do is get the X-pipe to transverse the passenger side front mount of the torque arm, but as you can see there's not a lot of room there.

 

If youre custom fabbing your exhaust, try this.

3" into the x, offset on the passenger side, then 2.5" coming out of the x, both on the passenger side, up and over the axle. It may be easiest to start with a premade Y pipe and cut the collector short, then fab the Y into an X and continue down.

This is the setup I have, except I have gutted cat shells, magnaflow 6" round mufflers and a center mount. Makes for a moderate sound at idle and part throttle, but a real screamer at WOT.

 

Sounds like what I'm looking to do with another OEM catback. Just bring the two pipes together close enough to join them with an (insert letter of the day here)-pipe, then both over the axle and into a pair of bullets, glasspacks, fart cans, I haven't decided yet.

 

Walmart sells a 10" diameter chrome wastepaper basket that you could use an an exhaust tip. that would look so hot!