Exhaust pipe size w/LS1 in a street rod??

[Mike52]

I'm getting ready to build the exhaust for the '32 Coupe. What are the optimal size pipes to run on a stock LS1, 2¼" or 2½"? Due to frame rails, engine placement, etc, I'll be using block hugger headers if that helps with the sizing.

Thanks,
Mike

['00_Z]

If you plan to keep the engine stock 2.25" duals will flow fine. You can run 2.5" also if you want it louder but it isn't necessary.

[WickedSuperSport]

well, LS1's come stock with 2.5" piping, so thats probably what you might want to use.

[KurtRardin]

How big is the collector on your headers?

For the love of God, do not listen to the size recommendations that an exhaust shop makes either, unless it's a sponsor here. Most shops think that an LS1 is an ol' 350, and that the same rules apply. Most of the aftermarket exhaust systems for LS1s are 3", but 2.5 would honestly be plenty, especially if its just going to be a cruiser.

You will know that your shop hasnt got a clue about LS engines if they mention their little catch phraze: "Back Pressure"

[Mike52]

Thanks to everyone.

Kurt, I won't be listening to an exhaust shop, I'll be the one fabbing this system. I've got a great, cheap (free) source for the stainless steel tubing including the bends, elbows, etc. I just needed to know the recommended size, looks like it will be 2½".

Thanks again,
Mike

[Hard Core Z28]

Dual 2.5" will be a good choice.

[Lopoetve]

what do most exhaust shops expect to use? I'm guessing if they want back pressure, they try to push 2" or the like?

[KurtRardin]

No, not quite that low, but they'll start rambling about how dual 3" pipe will make it loose power, burn more fuel, burn valves... and that an x pipe's job is to add back pressure and does not change exhaust tone... and that mandrel bent pipes don't flow any better than crush bent pipes.

I bought a welder and swear never to go to another shop that thinks my 5.7 liter is a 350.

[Lopoetve]

ah, gotcha. I'll remember that

[01ssreda4]

Originally Posted by Hard Core Z28

Dual 2.5" will be a good choice.

i agree, i would personally go with whatever size my header collector was or 3 inch whichever was bigger....

[thunderstruck507]

I have 2.25" on mine and as of now with this tune I don't make any more power with cutouts open than closed. Cutouts are a foot or less behind the headers, exhaust goes all the way to the back.

But if I were running a new system I would go 2.5" just to be safe and maybe be a little louder.

[sciff5]

Originally Posted by KurtRardin

No, not quite that low, but they'll start rambling about how dual 3" pipe will make it loose power, burn more fuel, burn valves... and that an x pipe's job is to add back pressure and does not change exhaust tone... and that mandrel bent pipes don't flow any better than crush bent pipes.

I bought a welder and swear never to go to another shop that thinks my 5.7 liter is a 350.

This is the biggest pile of horseshit I've ever heard. Dual 3" will if anything help it wont hurt.

I run true dual 3" all the way back and I had some of the best numbers for a bolt on ls1 at my local tuner, and then turned some of the fastest times ever run by a bolt on ls1 rx7

To the original poster, keep it simple and run exhaust the size of the collectors on your headers, which are probably 2.5". I think X pipe really makes the car sound better, but thats more opinion than anything else

[KurtRardin]

Originally Posted by sciff5

This is the biggest pile of horseshit I've ever heard. Dual 3" will if anything help it wont hurt.

That's the point that I was trying to make too, but most exhaust shops will try to tell you otherwise. You should have seen the looks when I proposed the idea of a 4" merge collector on my Y pipe... they thought I was crazy. Well, a cam, 4.10s, and a 4" y pipe later and I still get 28mpg on the highway.

[Daez]

Dual 3" here.