Exhaust Set-up: 454 with stock manifolds

[gdubya]

I am in the process of rebuilding my 70SS 454.  Running headers isn't an option as I want to keep it original and true to the car.

Any recommendations on how to go about getting the best performance out of the original manifolds?  Or just clean them up (or find replacements) and run it back?

Thanks in advance,

GW

[jft69z]

As you mentioned,  clean them up and install.

[MC1of80]

Like Joe stated, clean them up and install them. 

On "Barn Find" my 71 402 Monte the original manifolds were cracked. Installed a set we had "in stock". After that I installed pypes 2 1/2" head pipes into a (Also in stock) 2 1/2" flow master exhaust system that I removed the flowjunk mufflers and installed a better flowing dynomax ultraflo mufflers. With stock SS tips. 

[Marks71]

Just wanted to throw this out there. Research Extrude Hone. It’s a process of forcing an abrasive material through the manifold to smooth out the interior and improve  flow. Not sure of the cost or how much benefit is accomplished. Maybe Joe or someone here has had some experience with it. 

[Marks71]

31 minutes ago, Marks71 said:

Just wanted to throw this out there. Research Extrude Hone. It’s a process of forcing an abrasive material through the manifold to smooth out the interior and improve  flow. Not sure of the cost or how much benefit is accomplished. Maybe Joe or someone here has had some experience with it. 

My own post prompted me to do a little research. Apparently it’s quite expensive and some of the comments weren’t too good. Sorry 

[jft69z]

2 hours ago, Marks71 said:

Just wanted to throw this out there. Research Extrude Hone. It’s a process of forcing an abrasive material through the manifold to smooth out the interior and improve  flow. Not sure of the cost or how much benefit is accomplished. Maybe Joe or someone here has had some experience with it. 

Funny you mention that Mark. My first thought was to suggest Extrude Hone 🙂. That, and maybe a little exhaust port matching, but for something that sounds like a stock rebuild, it would probably net you about 0.5 horsepower. Certainly not worth the expense & why I said clean them up and go.

I think Holley/Hooker has some cast iron type manifolds out there that may have some flow benefits, but no personal experience. 

EDIT: I just looked on the Holley/Hooker site. It appears they don't have anything for Big Block Chevy. Just small block, LS/LT swaps, some Fords, etc.

I don't know if LS6 Chevelle manifolds are different than the LS5, but someone here will have the answer to that. Maybe they were bigger/flowed better because of the higher horsepower?

[70white402]

15 hours ago, jft69z said:

Funny you mention that Mark. My first thought was to suggest Extrude Hone 🙂. That, and maybe a little exhaust port matching, but for something that sounds like a stock rebuild, it would probably net you about 0.5 horsepower. Certainly not worth the expense & why I said clean them up and go.

I think Holley/Hooker has some cast iron type manifolds out there that may have some flow benefits, but no personal experience. 

EDIT: I just looked on the Holley/Hooker site. It appears they don't have anything for Big Block Chevy. Just small block, LS/LT swaps, some Fords, etc.

I don't know if LS6 Chevelle manifolds are different than the LS5, but someone here will have the answer to that. Maybe they were bigger/flowed better because of the higher horsepower?

Same manifolds. No difference.

[jft69z]

12 minutes ago, 70white402 said:

Same manifolds. No difference.

Great, thanks Jeff!

[420ponies]

Yeah, That's what my engine builder / previous employer uses on all his F.A.S.T. (Factory Appearing Stock Tire Race Class) builds. You ought to check these cars out, insane what they can run on stock 7" wide poly glass  tires. Amazing . Anyway, I'm going with stock manifolds (might port match is about all).These guys are running 565 Cu.In. motors. They also have a stock class that runs the more traditional sized motors ,but man, There Fast!!  In the F.A.S.T. Class, they do exhone  those manifolds, too the maximum clearances allowed. I follow Horsepower Depot on Youtube.

[gdubya]

Thanks for all the replies. I should have stated I am not doing a stock rebuild. I’m going to squeeze as much out of the motor as possible without compromising the integrity of the original block. Bored (.030 or .060) and stroked, roller, head work, etc. 

[jft69z]

If that's the case, you're probably going to have to live with the limitations of the cast manifolds, try the extrude hone like Mark & Jim mentioned, or get headers.