I am rebuilding a 400 engine from 67' Firebird. My 400 historically ran hot and I experienced either fuel delivery or vapor lock problems as fuel combustion was inconsistent. I removed entire fuel system (including tank), cleaned it out, replaces hoses, etc. and rebuilt the carb.

Considering machining the plenum on my stock GM manifold, installing a thin heat dissipater plate and installing a 1" carburetor spacer (Hamburger or Mr. Gasket products) to improve air flow, dissipate heat and fuel combustion.

Has anyone machined the OEM GM manifold and added dissipater plate and/or spacer?

I have not machined an OEM intake manifold. I did make a stainless steel heat shield combined with a commercially available insulating spacer. See enclosed. Solution helped but was not a cure. Lowering the float level slightly and ensuring cooling system performance was perfect also played a role in eradicating the problem.

Thank you. You took a interesting approach with the heat shield. I understand that SD Performance taps and plugs the two passages on the 67' intake manifold that pushed exhaust heat to the underside of the carb. Pontiac figured out that this was a bad design and corrected it in 68'.

The broader dimension heat shield is a novel idea. I ordered a heat dissipater plate from Ames and we'll see if it works. Thank you for sharing the CAD design for fabrication. You may want to consider starting an aftermarket products company!

Did you run into hood clearance issue with your carburetor spacer on a 67' Pontiac Firebird? I have not heard that a 1' spacer causes a hood clearance issue. I assume that the air cleaner height is a factor. Either way, thanks for the recommendation on the supplier.

Hood clearance issues, yes. Look close. Big block Chevy with air gap manifold. Aftermarket ram air cleaner with a K&N 1 1/4” drop base grafted to the bottom of it. It is a tight fit but it works and mates with the factory hood plate and hood.

Are you using the stock exhaust manifolds? If so make sure the heat riser bimetal coil is opening the flap in the passenger side manifold after warm up.