I have a rebuilt 455. .030 over with c heads that are ported and 2.125 intake valves installed. Hyd roller cam,lifters. Torker intake. I installed the Mr gasket fiber intake gaskets with no valley pan. The valley pan I had from mendello wont work with the roller lifters. The question I have is how prone is it on these motors to suck a intake gasket in to cause a vacuum leak? The motor ran fine at first, had about 12 inches of vacuum. Drove a few miles started missing. Took it back home and check valves and compression. Everything looked good at 170 lbs. Checked vacuum and it is very spiritic bouncing down to 0 and up. Havent took intake off yet, Plan on doing this weekend. Thought I would get some input from here to see if my thinking is correct. Thanks in advanced. What is the consensus of using the original style turkey tray on the torker intake or try the fiber again. I have no leaks on the top side.

 

From an obvious stand point the fiber gasket is much thicker that the original tray. I've used both over the years with good results. I swapped intakes last year and used the turkey tray just like factory.

A bouncing needle on a vacuum gauge lends me to think valve sealing. I'd look again at that. I wouldn't over look the pcv valve, brake booster lines or any vacuum lines as well. Lastly, checking plug wires and boots to ensure good connection.

 

I'd double check your valve adjustments again. Wide swings in vacuum is usually caused by valves not closing all the way. Doubt your manifold gasket choice is your issue.

 

Thanks I will check valve setting again