I'll be running roughly a 650hp blown engine. Already have hooker super comp headers and right now a dual 3 inch exhaust system but the ground clearance is terrible. It was ok in Germany but here back home it wont cut it. I would rather run a single 4" for its simplicity, but I'm worried about power loss. As long as it isnt killing more than 15 horses I'd be happy. I really dont want to fab up another dual 3 inch system. What do you guys think? Fab up a single 4" or continue with the dual 3. Both I want up and over the axle to put the mufflers in the rear to max ground clearance.

 

Thunder Racing did a whole series of dyno tests on exhaust systems and discovered that the difference between a 3.5 inch and 4 inch single exhaust was'nt very great: 5 to 10 HP. At the 500 HP level, even a good three-inch mandrel bent exhaust doesn't give up that much HP. Mufflers made the biggest difference.

They did a dyno test on a blown LS1 4th-gen and discovered that a Hooker Aerochamber, cut to 3.5 inches on the inlet, 3.5 inches on the single outlet, helped boost horsepower by nearly 40 HP over a Spintech muffler, when coupled to a 3.5 inch Mufflex pipe.

Dave Tuschoff has the nicest exhaust I've seen for a third-gen: Hooker long tubes to a 3-inch Y-pipe, that dump into a 3.5 inch Mufflex cat-back that has been adapted to a single in, single out Hooker Aerochamber muffler.

With a moderate fuel injected 383, he's trapping in the 11's at 118 MPH.

 

So if I made a custom 4", it should be suffice for 600hp? It would make things a lot easier. Im having trouble finding 4" mufflers though. I would like to get a single in, dual out one, but that might be impossible.
Oh and where would I get a 3" into 4" y-pipe?

 

In your case you don't have alot of options.....you NEED good ground clearance.....go with a custom 4" piece modeled after the 3" factory pipe. Custom 3" y pipe into the 4" up over the axle and then pic your poison from there. Thats about as good as it will get when ground clearance is important.

 

Ok, so no one sells a 3" into 4" y-pipe? I cant seem to find a 4' muffler either.

 

I custom built an exhaust system for my 82Z. I made a duel 3" to single 4" Y-pipe and it was easy.

If you look down a few threads under My Exhaust Pic or Picture you can see the 4" system I built. My car is lowered and it has tons of ground clearance. I also have a spintech 4" single inlet and 3" duel outlet. There are lots of mufflers for what your looking for.

PM me with any questions

 

Mufflex sells a 4" single and dual exit cat back exhaust. you would probably have to have a Y pipe fabbed up to the diameter you want. just a suggestion...

 

You could try Dr. Gas or spintech for the 3-4 reducer. Any time you get up into this size of exhaust it gets expensive.