big block exhaust

[tirebird]

I'm curious to see what type of exhaust members are using with their big blocks.

The builder of this car believed that stealth was best and ran 2 1/4" pipes out of the 3" collectors of the Headman headers to a crossflow muffler and dual tips. Very quiet..too quiet.

I'm running dual 3" pipes with dual Flowmaster Super 40's and turndown's.

Some experts say 3" pipes are too large even for an LS6 454, unless it's on a race car. What do you think?

[Chevy454]

What do you have done to the LS6? 3" *might* be a tad much, unless you're really wringing out the 454...

[tirebird]

No,.it's stock. I floored it yesterday morning on the way to the GoodGuys show and it seemed just as healthy as before, so I can't see any difference so far,...except for loudness. I'm carrying ear plugs in the glove box.

[SS4Real]

Unless you're over 500hp, 2 1/2" seems to be the recommended size. I spent some time at Doug Thorley's shop in SoCal and that's what they recommended. I've got a 2 1/2" ceramic coated mandrel bend system with Walker Dynomax Hemi Turbo's. The system was custom bent and installed using stock exhaust manifolds and ran $1500 with the H pipe. It's a work of art and not cheap but is quiet in the interior with no resonance. When you jump on it, it roars but doesn't overwhelm.

[Unreal]

I'm running 2-1/2" (or 2-1/4..can't remember)stainless chambered, made on the original GM tooling. Stock cast manifolds.

It's very loud...too loud!!

[Chevy454]

I agree with Jim, 3" is overkill for your combo...in fact, I would copy Jim's system to a "T"...LOVE those Dynomax Turbo mufflers...

[tirebird]

You guys may be right. It's a simple fix for me to go back to 21/2" and keep the turndowns. That will be my next car project. Thanks guys.

[njsteve]

I am running 3" from the headers back, in my 426 Hemi. The car puts out 397hp at the rear wheels with open headers and 385hp at the rear wheels with the 3" exhaust hooked up. This was a 45hp improvement over the stock 2-1/4" exhaust. The engine is stock with factory original cam. The same exhaust probably would not be a good idea if I was running stock exhaust manifolds.

In the same vein, my Trans Am's 1972 455 HO (stock 8.3 to 1 compression) had 3-1/2" exhaust put on by some crazy person. It had stock exhaust manifolds and four adapters welded together to up the pipe size to fit the 3-1/2" pipe and get this: 4" inlet mufflers . https://www.yenko.net/attachments/110429-adapter1.JPG
https://www.yenko.net/attachments/110432-adapter2.JPG
I think the guy must have found the mufflers and then figured he was 1/2 way to an exhaust system and had to use them. The car would barely run with that exhaust system. I will be going back to stock when we reassemble the car.

[tirebird]

Steve:
With Hedman long tube headers and the 3" exhaust, the car runs great. I know too much exhaust can reduce low end torque, but I don't see any degradation in my car's performance after putting in the 3" system. I've never dynoed the car, but taking the factory specs., and adding in the headers, the LS-6 is running some where north of 420hp/tq., at the wheels.