I am getting exhaust put on my Olds and the Mechanic is trying to sell me 2.25 head pipes and 2" tail pipes. The engine is a mild 71 455 with a cam. I went from 2" to 2.5" tail pipes on a 454 LS5 Chevelle and picked up at least .3 tenths at the track and a couple miles per hour. I'm thinking 2.25 the whole way, but why not 2.5?

Thanks for any advice.
Dave

 

I would go 2.5 all of the way with mandral bends. Sure helped wake up my 455

 

x2

 

I kinda thought 2.5 was the way to go. I think the shops like installing smaller pipe to make things easier.
Thanks guys,
Dave

 

Hey Dave, just curious what kind of prices you're being quoted to purchase and install your system.

 

I had a local guy that does a nice job quote me $300 for aluminized 2.25 headpipes, 2" tailpipes and mufflers. The price is right. He will allow me $50 because I have my own mufflers.
Dave

 

That's pretty cheap. I have a guy in Phoenix quoting me $590. That's with 2.5" pipe and Flowmaster 40s. Guess it's decent.

 

Anyone on here tried the larger diameter repro cast exhaust manifolds that mimic the originals? How about the ovalized 3 inch pipe I see advertised in this area?

 

Actually that is the stock size, at least in the mid-60s. But 2-1/2s are definitively better from the performance standpoint.

 

I put a crossover back of the trans and 2 1/2 pipes with stock bends ...

 

Link ...

plz ...

 

Whatever the outlet of your manifolds/headers are is as big as your headpipes should be.

If you have manifolds and the exit is 2.25, it does you no good- (actually probably hurts you) to run bigger headpipes.

If you have headers with a 3" collector or 2.5" collector, then run that size pipe. A lot of racers will cut off a 3" collector and weld on a 12" gradual reducer to go from 3" down to 2.5". (or from 3.5" to 3")

The idea with exhaust is it needs to gradually, and smoothly get smaller- so as to keep exhaust velocity up as it cools down. By the time the exhaust gets to the mufflers its cooled down enough that the size of the tailpipes really doesn't matter. Stock they stepped down one more size in tailpipes, but for performance, you could run the same size as the headpipes, or no tails at all- most performance tests show them to be roughly equal.

 

Here is the local company I see all the time at the swaps swelling oversize repro exhaust manifolds and oval pipes:

http://www.ramairrestoration.com

 

Thanks ...

I'll check out my car for which manifold I have ...

I have a stock set up so velocity may be more important than capacity ...