choosing exhaust for street/strip build on BB 383, 2.5" or 3" exhaust?

[skynimbus]

Currently running 2.25" dual exhaust with glasspacks.  Want the most power and performamce I can get outta the build on this motor.  Does larger pipe deliver more power or does more power simply require larger pipe?

[c00nhunterjoe]

The 2.5 will adequately power the 383 well into the 450hp range. 3" will give no more power, just a deeper amd louder exhaust.

[68X426]

3" exhaust may actually lose you some horsepower and torque.  There may not be sufficient back pressure from the system to help your heads/cam combo find its optimal production range. 

I recall someone's study on a dyno and that bigger exhausts failed to yield more power, in fact diminishing torque by something like 5%.  I'm sure the turbo tuner guys will weigh in, and the diesel guys will have their opinions.  I understand it as a matter of a carbed motor needs some proper degree of backpressure.  Too much is as bad as too little.  The time proven choice has been 2.5".

[RamZCharger]

I have read several articles on cut-outs that when dyno'd against a baseline being open yields more HP and TQ.  Not huge gains but certainly no reduction in power.  Wouldn't larger exhaust have a similar effect and isn't backpressure also more dependent on design of headers . . . ?

[alfaitalia]

....yes you will get more power and torque with open pipes.......but usually only higher up the rev range and at the cost of low down shove, which if you are street driver is where you really need it despite what traffic light grand prix racers may say! You need that back pressure to keep the unburnt fuel in the combustion chamber when the cam is on the overlap phase (both valves open when piston starts on the way back up.) I fitted a full race system on a turned Audi I had in about 92.....was flat as a witches tit below about 3000....then took off like a scolded cat.....not nice on the street where it spent all its time....so I swapped it out. Drag racers etc don't care about low down torque and just need to get the gases out fast as possible to make max power at high revs....hence the short open exhausts or even just 18 in or less fat, open tube headers on a pure drag weapon.

[c00nhunterjoe]

When done right, there will be no difference in et or mph in the 2 systems. I ran 3" full exhaust on my car and had no measurable difference co.pared to open header

[alfaitalia]

True....only really affects drivability on the street.

[Lennard]

No opinions,  just facts:

https://m.youtube.com/watch?v=_PVXvHkr-Vs

[alfaitalia]

Pretty much what most on here where saying.

[c00nhunterjoe]

No opinions,  just facts:

https://m.youtube.com/watch?v=_PVXvHkr-Vs

Thats a bit bias.... on a 600hp mill.... we are not talking about that, a better video would have been their 2.5 vs 3" test on a 355hp 350 chevy..... which is more like what the avg motor on these forums are.

https://youtu.be/bXQ-cXeri1Y

[skynimbus]

OK thanks,  2.5" it is then. 

[RallyeMike]

Another thing to consider - The big block chevy test was also with 2" primary tube headers. Not a header size typically found on the common street engine.