air leak on inlet manifold

[tuxman]

we have a air leek on inlet manifold from valee which creates hiccuping on the rundown have refitted it with new gaskets but has not sorted it anybody any ideas?

[davefiddes]

What heads, intake and gasket are you running? Have you done any work on the heads e.g. an angle mill that was also done to the intake?

Could be the gasket type is wrong for the heads and/or intake. Maybe there is a roughness on the intake that is causing it to fail to seat properly. Did you notice anything odd about the sealing pattern of the old gasket when you took it off?

[tuxman]

hi Dave inlet manifold is a edelbrock air gap no 7501 and it sits on performer rpm aly heads, gaskets are felpro 1205 with sealer fitted on all surfaces old gaskets were fitted without any sealer so i thought that was the problem,carb is a holly 750 d,p i did wonder if the manifold could be faulty ?ther does not appear to be any rough bits, only machine work done was to skim block

>> Edited by tuxman on Thursday 23 September 22:12

[davefiddes]

Sounds a reasonable setup. One tip I've read about (but not tried yet... - YMMV) to find a vacuum leak is to get a propane blowtorch (no, don't light it!!!) and to go round all of the suspect joints in the intake with the engine idling. If the engine suddenly picks up then you've just found your vacuum leak (because the propane is being sucked in and burned). Might help?

[Boosted Ls1]

tuxman said:

hi Dave inlet manifold is a edelbrock air gap no 7501 and it sits on performer rpm aly heads, gaskets are felpro 1205 with sealer fitted on all surfaces old gaskets were fitted without any sealer so i thought that was the problem,carb is a holly 750 d,p i did wonder if the manifold could be faulty ?ther does not appear to be any rough bits, only machine work done was to skim block >> Edited by tuxman on Thursday 23 September 22:12

How much was skimmed off the block? It's likely the manifold is sitting to high. To rectify this you need to skim the manifold faces, be careful who you use to do this. I'm assuming the block has lost about 1mm. Less then this and you shouldn't have this problem.

[US-GTR]

A trick I learned the hard way is to reinstall the intake manifold without the end seals (the ones that run between the heads) and replace with a smooth bead of silicone. This allows the sides of the manifold to seal better on the heads without having to over torque the intake bolts.

Besides using Propane, I have always used ether (aerosol starting fluid). It is a bit easier to use and direct at specific areas, and easier to control flow.

[tuxman]

thanks for replies,do not know how much was skimmed off block will contact machine shop to find out ,have tried to find leak with gas but because it draws air from valee its difficult to find ,could it be anything to do with carb butterflys? are there any thicker or softer gaskets i could use,i have used silicon on the ends not the cork gaskets

>> Edited by tuxman on Friday 24th September 18:43