Exhaust manifold flow efficiency

[Gary B. (66)]

I recall reading an article some years ago about a technique to improve the flow characteristics of a cart iron exhaust manifold by pumping an abrasive slurry through the manifold passages under high pressure. The slurry supposedly polished the internal walls and eroded away bumps and imperfections and perhaps even increased the cross sectional area thereby improving the flow and volume of exhaust gases. Does anyone remember reading about such a procedure and does anyone know if it actually works in terms in a documented increase in HP? If it works, what does it cost and does anyone have the name of a shop that could do the work?

Thanks,

Gary

[Page C.]

Re: Exhaust manifold flow efficiency

Hi Gary, Seems like I remember the article . I believe it was in some years back in Hot Rod Magazine. Will look thru some back issues when I get a chance. Have no idea if it was an improvement . Page Campbell

[Page C.]

Re: Exhaust manifold flow efficiency

Hi Gary, Seems like I remember the article . I believe it was in some years back in Hot Rod Magazine. Will look thru some back issues when I get a chance. Have no idea if it was an improvement . Page Campbell

[Jon Whiteley]

Re: Exhaust manifold flow efficiency

Gary,I believe the process you are referring to is called Extrude Hone and the company that developed this goes by the same name. I'm digging back in my memory with regards to this, but seem to recall that it was reported effective. You will probably have to check out magazines like Hot Rod,etc. for an advertisement or phone number. Maybe they have a website. Good luck!

[Jon Whiteley]

Re: Exhaust manifold flow efficiency

Gary,I believe the process you are referring to is called Extrude Hone and the company that developed this goes by the same name. I'm digging back in my memory with regards to this, but seem to recall that it was reported effective. You will probably have to check out magazines like Hot Rod,etc. for an advertisement or phone number. Maybe they have a website. Good luck!

[Joe L.]

Re: Exhaust manifold flow efficiency

Gary----

I would be extremely leery of modifying exhaust manifolds through use of the "extrude hone" process, which is primarily used for cylinder heads, or any other process. Many cross sections of an exhaust manifold are rather thin; removing material could weaken the casting, making it susceptible to cracking. Too much risk, in my opinion, for the small amount of gain.

As an alternative, if you don't require A.I.R. fittings and you don't already have them, use the 2-1/2" flange rams horn manifolds. These manifolds, GM casting numbers 3797901, 3797902, 3797942, or 3846563, are the best flowing exhaust manifolds ever used on a small block.

[Joe L.]

Re: Exhaust manifold flow efficiency

Gary----

I would be extremely leery of modifying exhaust manifolds through use of the "extrude hone" process, which is primarily used for cylinder heads, or any other process. Many cross sections of an exhaust manifold are rather thin; removing material could weaken the casting, making it susceptible to cracking. Too much risk, in my opinion, for the small amount of gain.

As an alternative, if you don't require A.I.R. fittings and you don't already have them, use the 2-1/2" flange rams horn manifolds. These manifolds, GM casting numbers 3797901, 3797902, 3797942, or 3846563, are the best flowing exhaust manifolds ever used on a small block.

[Bill W.]

Re: Exhaust manifold flow efficiency

Gary, There is a company in Wisconsin, forgot the name, they developed and applied this process to stock manifolds used in some classes of dirt stock car races, where, for noise abatment, headers were not allowed. The tests results I saw (several years ago) claimed 5-7 hp gain above 5000rpm. Doesn,t sound like a good deal to me. I like Joe's idea better, ran to 2.5 inch manifolds. Bill

[Bill W.]

Re: Exhaust manifold flow efficiency

Gary, There is a company in Wisconsin, forgot the name, they developed and applied this process to stock manifolds used in some classes of dirt stock car races, where, for noise abatment, headers were not allowed. The tests results I saw (several years ago) claimed 5-7 hp gain above 5000rpm. Doesn,t sound like a good deal to me. I like Joe's idea better, ran to 2.5 inch manifolds. Bill

[Gary Bosselman (2575)]

Re: Exhaust manifold flow efficiency

Guys,

Thanks for the tips. The company name is indeed Extrude Hone Corp, based in Irwin, PA. I think I got things confused and the article I read some years ago was about cylinder heads, not exhaust manifolds. In any case, I have a call in to the company to see about the cost for treating a pair of heads.

Gary

[Gary Bosselman (2575)]

Re: Exhaust manifold flow efficiency

Guys,

Thanks for the tips. The company name is indeed Extrude Hone Corp, based in Irwin, PA. I think I got things confused and the article I read some years ago was about cylinder heads, not exhaust manifolds. In any case, I have a call in to the company to see about the cost for treating a pair of heads.

Gary