gdubya Posted January 20 Share Posted January 20 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 Quote Link to comment Share on other sites More sharing options...
jft69z Posted January 20 Share Posted January 20 As you mentioned, clean them up and install. 2 Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted January 20 Share Posted January 20 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. 4 Quote Link to comment Share on other sites More sharing options...
Marks71 Posted January 20 Share Posted January 20 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. 1 Quote Link to comment Share on other sites More sharing options...
Marks71 Posted January 20 Share Posted January 20 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 1 Quote Link to comment Share on other sites More sharing options...
jft69z Posted January 20 Share Posted January 20 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? 2 Quote Link to comment Share on other sites More sharing options...
70white402 Posted January 21 Share Posted January 21 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. 1 Quote Link to comment Share on other sites More sharing options...
jft69z Posted January 21 Share Posted January 21 12 minutes ago, 70white402 said: Same manifolds. No difference. Great, thanks Jeff! Quote Link to comment Share on other sites More sharing options...
420ponies Posted January 21 Share Posted January 21 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. 1 Quote Link to comment Share on other sites More sharing options...
gdubya Posted January 21 Author Share Posted January 21 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. Quote Link to comment Share on other sites More sharing options...
jft69z Posted January 21 Share Posted January 21 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. 1 Quote Link to comment Share on other sites More sharing options...
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