The OEM exhaust manifolds look really rough on the inside with big edges/steps on both on the cylinder head side and the turbo side.

Did anyone find out if it makes any difference really to machine them to become smoother? (with a sub 600hp setup?)

 

Talk to Markski @ 911Tuning. He's ported and polished stock for a bunch of applications. My guess is you need to be at or above 600HP at the crank to see any difference.

 

That's what I heard... it's just that having one in hand and really seeing it makes you just wanna clean it up because it looks really bad. Even with "only" stock K24 + a flash. But not going to waste the time if there's no relevant difference.

 

From my understanding it's no real difference. It's 1 of those areas that differ from American muscle car HP. Changing the headers are a must on them but we are also talking German Engineering compared to US. 1 very much over compensates.

 

Hi,I did a thread on that about a 1year ago when I did it..All I can say is that....I know the early castings had alot of weld bead in the collector to cut down the I.D. size their and some weld bead over hang in the port area also....I bought a set off of this site that were off a that were pretty clean from the factory......I was hoping mine were like the dirty ones,lots of weld.....But my 2004 were also very clean with minimal weld build up...I took a die grinder and cleaned them up alittle...Was it worth it and did it help performance??...I dont think so because I had very clean ones to begin with....But if they are the older ones with alot of weld in the collector area,I believe opening them up would help because of the small Dia. that they are to begin with....IMO.....I know that their are many very high HP cars with stock ones out their..... Hope this helped....

 

It can't hurt. If you have them off, I would do it. I had Imagine Auto do mine way back, many years ago when it was first suggested. My car has always run strong times in the 1/4 mile for it's various levels and I feel it's because I always had a few tweaks to the pre and post turbo air flow.

This is what we did...ported and ceramic coated - they have been on the car for 7 years and about 75,000 miles without failure. Stephen did a nice job on these.

 

I have done this and I believe it is a worthwhile mod, especially since if you do it yourself, its free. My old headers had a ton of "excess" material on the inside. The headers I bought off the board looked way cleaner, but there was still a lot of excess material to remove. Kevin from UMW has a great post on this on that other board detailing the process, the tools to use, the amount of material to remove (don't go too far!), and his opinions on why, unless you are at crazy hp levels, this is a very advantagous mod. Good luck!

 

Johns right, if they're off it won't hurt. By the way those black headers look good.

 

You will never notice any benefit on our cars (at any HP level)

 

I don't think you could ever feel the difference during driving, but I would not be surprised if a timed event such as 1/4 mile or 60-130 benefited by this modification, even if by a 10th or two. In fact, I would expect it. Supposedly there were dynoes done with this mod that showed a power increase.

 

You MIGHT be right...BUT...I think if you had manifolds with allot of weld build up to reduce the inner diameter in the collector area and took that bead weld out it would help in spool time and a power increase..It is a small diameter to begin with and any enlarging in that area would be beneficial...IMO..

 

I think Kevin the tuner/builder from UMW did a test comparing dirty ones with ported ones and saw an increase..It is on Rennlists site...

 

I defenantly don't want to miss represent Marski. But my understanding is you have to weld them on the outside before you port and polish in the inside. Then you are not removing the only weld that holds them. It's also why I suggested to contact him on how to do this.

I agree, at a certain HP it can make a slight difference. Plus if you do it right how can a cleaner air flow be worse?

I wish Marski would chime in, I don't want to say something on his behalf that isn't accurate.

 

1. 'Cleaning up' is different than 'porting'... as Tony said, don't get into structure.

2. With FI, the resistance in the header is probably not a major factor...someone mentioned german engineering and american muscle.... not the issue. The S62 BMW suffers from poor headers and upgraded headers have a dramatic power increase, but that is NA, like American muscle.

 

Port & Polish is the term I used and you are correct. Its just habit I guess when talking of cleaning up heads and exaust areas.
I mentioned the German vs American HP as well. I asked this Q 2 years ago and got the answers I've repeated.
But to use your correct term, to clean up or polish the inside can't hurt. It may be over kill but for people who has OCD like me it makes me feel better.

Still, Mark, Todd, and others told me the same thing. Clean them up won't hurt but if your not running real high HP #s it won't matter.