What collector gaskets are you using? I am using the 2 1/2" NAPA for a 71 Impala. The reason I ask is I'm still having problems with air getting into my headers and messing the O2 sensor up. Could the height of the gasket be to small and when the collector flange is tightened up against the header flange the gasket is crushing too much?
Tks.
oh, I have 1 5/8" SLP's

 

Hey Rob, I'm using a Fel-Pro 9587 (2 17/32" packing). I've had good luck with them.

 

im using Felpro #60986.. they also work great for me , fit really good