exhaust manifold flowing

[cawley]

Has anyone or knows someone that ported or used acid to get there exhaust manifolds to flow as good as headers ? I have heard of people using acid but I don't know how true it is. Has anyone done flow test on exhaust manifolds ?

 

[ValiantOne]

Can't add to the conversation, but I'm going to follow it. I am a "header hater" and would love to keep my 340 manifolds on my upcoming build.

 

[jazak5]

I do recall a process called extrude honing but to find someone to do it would most likely have to have them shipped out

 

[340doc]

I read an article years ago about a method called extrude honing. A very firm abrasive media is forced through the manifold repeatedly until it enlarges and smooth's the inner walls. You'll have to search it up. If I remember, the flow numbers increased but still fell short of headers.

 

[toolmanmike]

From what I've read it smooths but doesn't remove much material. It improves flow but not by much. I have a pic on my laptop but not on my phone.

Extrude Honing | Bonehead Performance

 

[toolmanmike]

Here's a photo of a centerr port of a small block manifold. It would be interesting to flow and dyno before and after.

 

[cawley]

Here is what I am going to be up to (when I get the money) My goal is to make my 69 383 barracuda engine look as stock as possible but run in the mid to low 11s.

 

[RustyRatRod]

Talk to @Treblig, I mean Treblog. He may not have flowed them, but he modifies stock manifolds and does a really nice job on them.

 

[Rapid Robert]

there was a utube vid on using some blast media at home sorta like the commercial extrude hone process & reportedly there was a significant gain in flow. I'm gonna see if I can retrieve it. EDIT found it: filled capped up ex man with muriatic acid/let set for 2 hrs/drain & refill with fresh acid/repeat 4 times. manifold held 16% more water when done (water used to check volume/capacity). I was impressed.