heat shields

[greencar]

Are the metal heat shields made by GM that fit between the carb and manifold effective in preventing vapor lock? Thanks for any input.

[Cliff Ruggles]

No, they were used on intakes that had hot exhaust gasses routed up under the carburetor.  In the late 60's they used the heat to warm up the upper part of the intake and the carburetor.  This allowed for leaner jetting to help meet emission standards in place at that time.

Some later intakes use the shield to isolate EGR passages under the carburetor.

A steel plate is not an insulator of any sort.....Cliff

[Schurkey]

Kinda depends on WHICH heat shield we're talking about.

GM sold both a squarebore and a spreadbore heat shield, aluminum with gaskets on both sides.  They wouldn't prevent vapor lock, because that happens in the fuel plumbing on the suction side of the engine-driven fuel pump.  They were effective in reducing fuel percolation (boiling) in the float bowls, though.

The squarebore shield is still available from Holley, P/N 108-70; I think GM has discontinued both kinds.  It would be extremely easy to duplicate these heat shields using aluminum sheet and some carb base gaskets.

I bought a GM spreadbore shield off of eBay years ago, it's still in the paper wrapper.

Here's a photo of the Holley squarebore unit:  (disassembled--mine have the gaskets stapled to the aluminum.)

[Schurkey]

Oh, yeah.  Found the GM part numbers:

Squarebore = 3969835

Spreadbore =3969837

[Schurkey]

Can't get this photo to post:

http://www.alldeysparts.com/cart.php?target=image&action=product_image&id=1073