In a 400 to 450 HP motor would there be much of a difference?? Lets say both motors have headers.

2.5" dual head pipes/mandrel bent into 3" single pipe with a 3" cut out...or

2.5" duals with H pipe and a pair of perf muff's.

I asked this Q on another site and was told single 3 would have more restriction than duels

Was it with an exhaust cut out???

When i was at the point of replacing the exhaust i went with what my muffler person recomended 2.5" duals with out the H pipe and a pair of perf muff's.
i read the H pipe or cross overs would improve low end and would allow the engine for a better flow and balance....im glad i did not go with the H pipe or cross over... im sure i will cause "many" to disagree with me on this Thread, but we can agree to disagree...i just like the Rough, Loud sounding Mis,each pipe on its own, not evenly sounding rap that it has...might just be the extreme duration on my cam...but i can hear it well..Just enough to speed your heart up...when i fire up....know what i mean....Chris

Yeah, this set up would not be for my Camaro. Its for my Jeep. I currently have 2.5" duals mandrel bent to a Flowmaster Y pipe . This exits through a long straight 3" pipe to a 3 chamber delta flow muffler. The new 396bbc going in will most likely make around 400 to 425hp. So I was thinking about either adding an exhaust cut out for when I amd running mud/sand races or just upgraded the single pipe to 3.5" and no cut out.

Well, I would guess you are aiming at high HP rather than low end torque, considering the races you plan on running. This in mind, I would go with the duals. On the other hand, I don't think the big single will restrict you a whole lot in any way, but think of it as being more simple, and less to go wrong with. In true duals, you have twice the possibility of a tube falling off over the dunes. Again, hardly and issue worth considering. So what do I suggest? Well, that one is simple: which ever one is most cost effective. ;)

A single 3" is equal to dual 2 1/4". IMO you will lose HP with the single 3" compared to dual 2.5" with good mufflers.

thats why alot of guys w/4th gen ls1 cars run duals 3'' the single is cool for street w/ cut out but for most braket/street cars I see alot of duals the only reason I didn't go w/duals on my 93 is because its a firehawk and I wanted it to look mostly stock

A single 3" is equal to dual 2 1/4". IMO you will lose HP with the single 3" compared to dual 2.5" with good mufflers.

Lonnie, What about if there is a cut out used before the muffler during racing only?? Do you think the uncapped 3" will flwo more than a muffed 2.5"?

I can only guess, but I'd say no. A lot of straight through mufflers and others don't hurt flow much if at all. The area of a 3" pipe is quite a bit smaller than the area of two 2.5" pipes. Pi*r squared: 7.07 vs 9.82. The single 3 is about 28% smaller. You would need a single 3.5 to almost equal dual 2.5's, and it is still slightly smaller. You can probably run almost any dual 2.5 mufflers and still outflow the single 3". With 450 real HP, I think you will be down quite a bit.

Actually the area of dual 2 1/4" pipes is 7.95. Bigger than a single 3" also.

I think my math is correct. I'm sure someone will let me know if it's not.

Hmm.............maybe I will just step up the single pipe to 3.5" down the road and forget about the cut out.

Dr Gas has oval tubing. The 2.5 X 4 should be good. Oval mufflers too, I think spintechs.

What was your reason for not wanting dual 2.5"?

I have dual transfer cases in it and they are clocked flat for more ground clearence. This allows zero room on the passenger side for exhaust pipe routing. So I have to run a single set up. The Dr gas oval stuff would work sweet huh....