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muscledelivery

Skimming manifolds

Are you guys Skimming the mating surfaces of your exhaust manifolds before refitting them? I've got used facelift manifolds that I'm taking off my car and wondered if it would be advisable to skim them before I refit to my new engine? Cheers
Burnzybubbles

If your running 500bhp then it's probably not a bad idea to just have the lightest skim to get it perfectly flat, it just gives the gasket a better chance, if it was me I probably would.
okkim

It is not necesssary, just check that it looks ok. I have never done it, and never had any problems. The power lever doesn't matter.
Burnzybubbles

How does the power level not matter? To produce 500bhp the gases are going to be under a higher pressure when released out the chamber compared to a standard car, I'd agree that checking the manifold for straightness first just incase it's not needed.
mikey-s

I wouldn't bother myself,  they would have to be seriously warped to not seal, plus I've never seen one leaking from that joint.   Just use new gaskets and you'll be fine.
Aragorn

Mine leaked from there, but it turned out to be a broken stud!

So maybe replacing the studs is a good idea when its off.
muscledelivery

Ok guys nice one I'll just give them a rub and I've got new oem gaskets to put on and new nuts. I've head of them leaking but I think it was new aftermarket tubular ones but they probably weren't machined after they were built.
muscledelivery

Also is there a tightening sequence or method you are using, im a mechanic but I just don't need to be taking the engine out again for a blowing manifold.
mikey-s

Just go from the middle outwards and you'll be fine.
okkim

Burnzybubbles wrote:
How does the power level not matter? To produce 500bhp the gases are going to be under a higher pressure when released out the chamber compared to a standard car, I'd agree that checking the manifold for straightness first just incase it's not needed.


It doesn't matter at these power levels where these manifolds are used. What I know, it has never been leaking from the standard power lever to the 600 hp! So in that experience I can say that it doesn't matter. The exhaust pressure isn't so big and hot that it would start to warp the flanges.
Burnzybubbles

okkim wrote:

It doesn't matter at these power levels where these manifolds are used. What I know, it has never been leaking from the standard power lever to the 600 hp! So in that experience I can say that it doesn't matter. The exhaust pressure isn't so big and hot that it would start to warp the flanges.


Fair enough, I'd still check it properly and have a clean surface for the gasket to seal against, no point in relying on luck if the engine has to come out again to repair the issue.
okkim

Yes of course the surfaces need to be clean.
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