Does anyone know the maximum horsepower a 3 inch exhaust will support? I have dual cats that merge in one Borla cat-back. I'd like to build my engine as a supercharged 383, but from reading some posts it seems people making 600 hp run a 4 inch exhaust. Did I just shoot myself in the foot by buying the Borla setup (or any other 3 inch cat-back for that matter)?

 

It will hold you back some at that power level but I dont think you neccesarilly shot your self in the foot. Is the Borla a straight thru muffler? I picked up almost 3mph by going from a single 3" flowmaster to a dynomax race bullet.I am hoping to try out dual 3" this friday.I am expecting to pick up another 2-3 mph in the 1/4 mile.

 

Once you are up to those power levels, you are gonna want to dump the single exhaust setups and get a set of 2.5 - 3" duals made.

 

Doh! Can a dual exhaust setup follow the same routing the single exhaust does? I know the muscle car way is to just go straight back (even on the driver side), but that sacrifices ground clearance. And then, there's the question of having two mufflers back there...doesn't seem like there's a lot of room for that. The other question would be, how much power can the single 3 inch system support?

 

Ground clearance isnt really an issue on my 383 Nova but what i did was right at the end of the header i bought bolt up extenions and attaced my dual flowmasters on both the extensions and tucked them up under the body. they exit before the rearend houseing but not the popular "prostreeet" style side exits. they are tucked close to my floorpan and have trurn downs faceing at a angle so it exits out the side yet retains clearance of a catback ill take a pictures in a few minutes to show you what i mean till then later

 

i havent seen the underside of many camaros so i dont know if it will work but heres the way it exits

 

To answer 84firebird383, yes the Borla system besides having a free flowing muffler, has the option to bypass the muffler altogether on race days (the exhaust gases can just exit straight through right tail pipe). Think a 3 inch is still sufficient?
For Teal91rs, the third gens have the right side of the floorboard (under passenger seat) raised to accomodate the exhaust pipes. Your setup looks like it would reduce ground clearance on driver side for sure (again on a third gen). Besides, I don't think you're running cats, which is a must around where I live.
I know Ferrari's can make that power, have the ground clearance and pass e-check. Can't a third gen pull that off?

 

400 rwhp is when you see the need for going larger than 3". A single 4" can support what you need or just install a cut-out. That is what you really should do with that much power.

 

Me not running cats what would lead you to think that! hehe i think cats where required after 1978? but besides that shifty hit it right on the head a cutout is the way to go! a muffler shop can probly fab up a single 4 inch exaust into a muffler with dual outlets easyly and with a cutout it should be more then you will ever need when that exaust is quarked up.also clearence and 500hp dont really mix lo.l emissions on a 500hp car with cats is really pushing it man. just my opinion this 383 n/a with no cats and only running a 12.0-12.3 is totaly failing emissions just immagne 500 blown hp's are. emissions is a little outa your grasp there expicaly with a cutout along with a 4' exaust youll fail visualy. so i think this 500hp goal is a little hard to obtain but thats just my opinion i have no clue about emissions so just ignore me! also when floirda had emissons our 69 camaro with an ls6 (454 remanufactured ls6) it had a documented 500hp and 600 footpounds of torqe (this is net flywheel power it rebuilt and dynoed by us in the 80's its an orginal from a vellie ) with 2.5 inch exaust it failed baddly. so just rethink this 500hp goal and rember the goventment is out to kill the hobbie!

 

Thanks for everyone's input. I'm rethinking the 600 hp goal and instead of a supercharger spend the money on lighter components like an aluminum block. Shaving weight is the other way to go fast.
Teal91rs, you're right about the government.

 

I only have a 3" on my car. Terry Houston 3" downpipe into a SLP 2OTL. I don't think it hurts performance that much. Best ET is in sig but I've run 121.4 as a best mph with a different chip(just couldn't spool on the launch with it)

Haven't dynoed the car since being stock but the online calculators claim over 430rwhp and 520HP.

As for emissions, I just put a cat on and went to the emissions station. Passed easily on the treadmill. No other changes Took the cat off when I got home. Its really just chip tuning to get it to pass. FWIW, my car has 50# injectors.

 

I think you would be happier with a superharger and your 3" borla than an aluminum block

 

Stumbled on this old thread, but wow, how things have changed in the 20 years since this thread was made.
It's a good read, enjoy.