I saw some exhaust manifolds that were extrode honed.What exactly do they do? enlarge the inside? thanks

 

Extrude honing is where they force a putty-like substance through the port starting with a very coarse grade and working there way down to a finer grade for a final polish. It smooths and slighty opens up the port.

 

And it's very expensive and on our intakes, you won't see much improvement.

 

Cool thanks

 

SLP had the exhaust manifolds on the 1997 LT4 SS/Firehawk extrude honed to help them meet their advertised 330HP figure. As was described, the process forces a putty like substance through the manifold that smoothes and polishes the walls by removing some material. One of the SLP techs that worked on the LT4 project stated that this made the manifolds flow close to what the SLP shorty (97 style) headers do. They did this on the LT4 cars as they were having a hard time getting the 330HP because they were stuck using the stock LT1 programming due to emissions certification. My car bone stock other than ECM tuning made 311RWHP, whereas most bone stock LT4 Vettes make 300RWHP. Considering that the LT4 Vettes have a better exhaust design (true dual, with manifolds similar to shorty headers) than stock f-bodies, I would tend to believe SLP's claim that the extrude honed manifolds do flow about the same as their 96/97 style shorty headers.

Honestly though, unless you are going for the sleeper look, I'd go for long tube headers instead.

 

Im soo lazy and dont wanna do headers. My friend at a muffler shop quoted me $300 to do headers and he keeps car for a week or so and works on it when he can.

 

Exhaust manifolds are going to be 80% of the work to do headers. Also, you should be able to get headers installed for around $150-$180 in one day.

 

dude, headers arent that hard to install. Ive installed 5 sets in LT1s. Edelbrock, 2 Pacesetters LT, and 2 MACs. Go with some MACs or Pacesetters. MACs will be cheaper and make plugs 10x easier.

 

Can you install MAC's from the top like the pacesetters? Where is a good place to get them? Do they work as good as some of the other name brands?

 

I live about 3 miles away from one of the Extrude Hone facilities. I talked at
length with the manager and for a set of cast iron exhaust manifolds the
process will remove material that equates to about 5-7% of the internal
volume of the manifold. Port matching is also part of the service which is in
the $625 range for a set of v8 exhaust manifolds. The process also removes
material where there is the most resistance to flow such as edges, restrictions,
etc.

I thought about it and then passed after I finished port matching my manifolds.
I was pretty pleased with the way my manifolds came out so the $625 did not
sound so appealing. Unfortunately I will not be able to provide dyno results on
the manifold work because I did a cam change at the same time. I may be able
to estimate it, but it would be a guess.

The intake manifolds for the Ford Lightning are Extrude Honed and I have heard
that it's worth 15-20 rwhp. As mentioned above, the LT1 intake would not
benefit much from the process. If you have the $$, I think it would provide
a significant improvement to cast iron exhaust manifolds.

 

Hey trueduals,
Why doesn't the Lt manifold benefit much from porting. Is it because it is already pretty good?

 

I'm just repeating what someone else told me but the LT1 manifold is
already open and a good port matching is all that is necessary. This
is probably why the extrude hone process does not do much.