There are a lot of differing opinions concerning this topic. Some people say 2.5" is sufficient, while others say 3" is best. Would a 3" true dual x-pipe setup be overkill on a full bolt-on car with nitrous? The TSP true dual setup is appealing, but I don't know if 3" would be too much for a bolt-on/spray car.

 

doesnt really matter how big it is... the bigger the better, although you must make sure your cam is suffecently designed to handle the lack of backpressure...

but of course someone correct me if i'm wrong.

 

What do ya think cars with open headers do for back pressure?
Back pressure isn't any good at all. Ya may need to tune for it and that is because the intake is working efficient.

 

I didnt say it was good, but thats what the cam works with, the less back preasure the better,
Open headers still have back preasure, they have to take a few turns, but no real bottle necks...
in any event it should work just fine... maybe a different cam or you might have a differnt power band, but all is fine

 

3" true dual x-pipe setup all the way

 

If you plan on taking them over the axle, you may want to consider 2.5" to make things easier.

 

Since you asked so nicely...

Bigger (than necessary) isn't always better. That applies to a few other things also.

Take a clue from GM. The 505 fwhp LS7 in the new Z06 has 3 inch true duals, with "cutouts" in the mufflers for high power/high rpm. Smooth flowing 3 inchers with nonrestrictive mufflers will support over 600 fwhp.

If BD380 isn't going much over 400 fwhp NA, 2-1/2 duals with the proper mufflers should be good even with a reasonable amount of spray. Besides, it's a lot easier and cheaper (and less weight) to hang 2-1/2 than 3 inch pipes as SS MPSTR just said.

Now if you are going well over 500 NA (430++ rwhp) NA, then 3 inch true duals would be helpful. I'd consider 3 inches back to 3 inch Magnaflow or Dynomax Ultraflow welded mufflers and then step down to 2-1/2 inch mandrel bend tailpipes. See this for why:

http://web.camaross.com/forums/showthread.php?t=397741

As fow camshaft timing, your engne designer should take into consideration the exhaust system, especially if he did a custom cam for your vehicle. If you are in the up-to-400 rwhp range, any cam that works assumes a fairly freeflowing system. Don't get jung up on this until you are looking for the last few % either for racing or something like the Engine Masters.

FWIW, properly designed headers and collectors can have zero backpressure, and in fact less than zero if they are correctly tuned.

Oh, yeah, 3 inchers are almost always louder than 2-1/2s.

 

so you are saying, if i get my 470 hp engine back, and i throw either a super or a turbo on there (havent decided yet), and get her on the juice as well, i will need atleast 3"

 

I'm guessing you might be north of 600 fwhp then. IF you have a chassis that will put it to the ground (your stock one won't), yeah, go 3 inches.

Before you get too carried away choosing exhaust pipe size, decide if you have enough funding to build a 600++ hp blown engine and the chassis/driveline which will handle it. Most folks don't plan enough cash for both, so they get a poser. Bet there are a lot of them in your area.

FWIW, will you be doing a lot of highway cruising with this blown monster? I ask, because the 6-speeds available have .50 or so 6th gear. Even with a LOT or rear gear, this won't be super useful to you. You might look at a Tremec TKO 3550 series 5 speed. Nice selection of gear ratios and 600 lb-ft continuous rating. Do some of your own research. It's fun. Google is your friend.

 

yea I figured north of 600 hp, but i wasnt planning on shelling it all out at once, I wanted my 470 hp motor, to be built and it is all forged so i figure if i get bored with that I can always put some extra goodies on...

 

As I said, my car has stock heads and a stock cam. It's a bolt-on car with spray. The topic got sidetracked and my question was never answered. Would 3" be too much? And no, I don't plan to take it over the axle. It will have dumps.

 

Too much cost yes, too little ground clearance, yes. And i personally think 2.5 in sounds better than 3 although ive never heard back to back on the exact same engine.

And i think bigger isnt always better...why not just have 2 in primary headers? Because it would actually kill power on and lt1 and not make much sense unless you were making crazy power.

 

Sorry. I thought this covered it:

You ain't makin over 400 with stock heads and cam, so, IMO, unless you are spraying for 600+ fwhp, good 2-1/2 mandrel bent true duals with low restriction mufflers will be sufficient. If you are at 600 with stock heads, cam and internals, you aren't likely to see that very long.

 

But 400hp is 400hp. What difference does it make if it's making that power on spray or on motor? The car won't be raced on motor, therefore I don't care how it performs on motor. Basically you're saying that 3" piping is beneficial at 400hp, which the car should make on spray, correct? Or are you saying that a 400hp motor car with the addition of spray would necessitate the use of 3" piping?

 

A dual 3" exhaust is a big exhaust...bigger than most realize.

A 4" Mufflex system is smaller than a dual 3" system and there are some very fast cars running a 4" (even 3.5") systems.