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Intake manifold leak - possible causes? 120-130

posted by  spectratone on  Sat Dec 8 18:10 CST 2007
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last visit: Wed Feb 8 21:35 CST 2012
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I'm beginning to suspect I may have an intake manifold leak, probably between the head and the manifold. Vacuum is around 16.5 inches at idle, and the car acts like it's too lean, especially when cold. It's sputters and sneezes right after startup even with the chokes pulled out on the Mikuni's. I also can't get a stable idle below 1000 RPM, and low RPM torque is poor.

I'm running premium fuel, timing is at 15 deg., distributor has the Pertronix kit installed with Flamethrower coil. MSD6 ignition, NGK plugs gapped at .035, spiral wound silicon plug wires. The engine is stock B20F specification with injector holes plugged with threaded hole plugs, with less than 1000 miles on a complete rebuild.

I'm using a FI exhaust manifold with the aluminum intake manifold. The mounting flange thickness of the intake and exhaust is different, so I had a machinist buddy at work fabricate some stepped washers for me; beautifully and precisely made... but I'm starting to wonder if they could be part of the problem, here's why...

The holes in the stepped washers are barely larger than the studs that the washers fit over, and I'm starting to think that maybe those holes need to be a little larger, to allow those washers to tilt a little bit when thermal expansion or contraction of the manifolds is taking place.

I've noticed the (flat) washers Volvo used on the B18's seem to have a generous amount of slop in those holes; I've also observed one surface of the factory washers is domed quite a bit. Is this something I should be focusing on, as something my stepped washers should have?

The only other issues I can think of would be a crappy gasket, or a problem with the split intake port sealing rings.

I checked the intake manifold mounting flange on the granite block at work, and it looked nice and level.

If their is an air leak, it has to be on the underside of the intake manifold, BTW; I did the bit with spraying WD40 on the manifold to head area from the topside already, and it had no effect.

Any thoughts would be appreciated.

Bill






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