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Pulled old Holley intake off '71 455. In the center of the heads are a square exhaust passage, then directly above that are thin rectangular passages which appear to be cooling passages, which PO just had plugged with silicone. If this is part of the pressurized cooling system, how come it wasn't leaking with just a dab of silicone on it? (Top of intake JUST covered the top of passage). Edelbrock intake going back on, and has the same pattern as the Holley. Is this narrow passage only intended to heat up the intake for cold starts, or is this part of the cooling system? Can I block both of these passages off with metal and industrial strength adhesive? (I don't want any heat source going under my carburetor. It's 90 degrees here in the winter, and I've got an electric choke). THANKS.
 

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That is the heat crossover, pumps exhaust to heat the carb. I also block it off, I live in FL. No water in the middle. If the intake is the wrong year for the motor it can leave the port uncovered and cause an exhaust leak, trust me, I know. Just block it off and you are good.
 

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In the latest issue of "High Performance Pontiac" they show how to block it off with furnace cement. Check highperformancepontiac.com, they might have the article posted, or go buy the Jan 13 issue.
 
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