Does anyone know what the minimum gap is for the intake to china wall? I had my manifold machined so the holes would line up and now the gap between the intake and the china wall is much closer. Without compressing the gaskets, the tightest I have is in the rear at .030. I just don't want the manifold to bottom out on the rails. Thank you.

 

That seems kind of tight if it's just sitting there - maybe if you have some old intake gaskets you can torque it down and see what you get.

 

Even tighter after torquing them. The tightest side (rails are a little uneven) measures .020 torqued. I am going to take it back to the machine shop and have them mill the rails again. What gap am I shooting for? I don't want a tight gap because of contraction/expansion of the metals on a thin layer of RTV. It seems to me it would break the seal the thinner the layer of RTV, right?

I'll post the compressed thickness of the gaskets when I pull it apart for future reference for those who mill heads and need to mill the intake.

 

Intake gaskets were .062 new (Felpro MS95580) and ~.058 compressed after torqued (71 in/lbs & 35 Ft/lbs) . Doesn't seem like much but my china wall clearance went from .040 to .020. Hope this helps someone in the future.

 

Did you have the flanges that touch the intake gaskets machined? Isn't the bottom of the intake supposed to be machined to compensate for taking down the other material?

I'm not sure how much can be taken off any of the surfaces, but maybe someone else with experience in machining the intake can chime in for advice.

 

Yes, I had the flanges cut .050 and they took the rails down by hand. They said they couldn't get it in the machine because it wasn't flat all the way across the bottom of the manifold. The flanges seem to fit nice, just need to gap the rails.

 

The angles and precision on the flange cut is obviously critical to the sealing of the intake surfaces. The end rails are not as big a deal because as long as you're sealing the ends with silicone, they don't have to be nearly as precise. If you have the time and equipment it's not difficult to set up on a small mill and make the cut. I've done it several times without causing any problems. It requires some imagination and time to get the set-up right but just about any gap from .020 to .040" will get the job done without creating leakage problems. I've effectively sealed end rails with considerably wider gaps than .040" on race cars on many occasions but that's a situation where function is more important than form. I've seen racers cut the end rails in the pits with a body grinder. It wasn't pretty but it sealed.

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I have the rails down to a .030 gap with the manifold torqued down. It wasn't too bad, used a belt sander and hand-filed the high spots. Took a while but the cut is pretty even (roughly .005 diff across the gap). I think this will get it done. Thanks to everyone who provided input.