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Old 07-18-2005, 03:24 PM
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Intake manifold temperature and gaskets

When I received my E/B EPS intake manifold from Northern Auto Parts, not only did I get the intake gaskets that I ordered but also the gaskets that were inside the manifold box (I did'nt know they'd be part of the kit). I used the gaskets I ordered and chose not to use Edelbrock's gaskets. My question is this - the Edelbrock gaskets came with 4 block off plates that have 1 7/16" sized hole in each. What are these plates for? I first thought they'd be exhaust crossover restrictors but if that was the case there'd be only 2, not 4. Why I'm asking is that my intake gets very hot with a surface temperature of 180 degrees. It just seems overly hot for my liking and I'm thinking of reducing it's temperature by blocking off the exhaust crossovers. How is this done and does it make a difference to the temp' reached by the manifold? My Holley 600 will ultimately percolate and flood in the primaries, even with the float level lowered. I never had this prob with the 750. Could the fuel pump pressure be a little too high? It's currently at 45kpa, which from my calculations should be around 7psi. I made a 1/2 inch carb' spacer out of plywood and even this ultimately had no effect. Any suggestions would be welcomed.

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Old 07-18-2005, 03:28 PM
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In the sets that I've used, there were 4 plates, one went on one side of the gasket and the other snapped in from the other side. A pair for each gasket.

The inserts with the smaller holes help to reduce the exhaust crossover and help keep the intake temp down. Personally, if you have cold weather at all, I'd use the supplied block off plates and not block them completely. "Some" carb heat is good, especially in the winter.

Being a cabinet maker, I like the idea of the plywood spacer!!! LOL Good job!!

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Old 07-18-2005, 04:44 PM
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I doubt that you will get your manifold temperature much below 180 degrees since the engine water circulates through it and plus you will get heat transfer from heads. Whatever temperature your engine runs will probably be close to the same temperature that your manifold will be.

Unless you live in a very cold area I would block off the heat risers totally. The heat riser is only of value when first starting and running the car in cold weather. Once the engine is warmed up, then the heat riser becomes detrimental from a power producing standpoint because you want the intake charge as cool as you can get it. The cooler the incoming air, the denser the charge and the denser the charge, the more power the engine will make. Heating up the incoming air just reduces the power output.

You can block off the heat risers with two pieces of thin steel shim stock cut to cover the hole in the intake manifold gasket. You can probably use material up to .030" thick without a problem. If it is too thin, eventually the exhaust gas might burn a hole in it.
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Old 07-19-2005, 12:22 AM
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Thanks for the replies fellas. I did'nt know the shim plates clipped together to form one......but now I do! JmDavis, that pretty much sums up what I was thinking in that ultimately the engine heat will transfer to the manifold. I was wondering if anyone has seen lower peak manifold temperatures after blocking off the crossover. I think I'll just have to nut this one out! Maybe I'll fit the centre hung fuel bowls from my 750 onto the 600 and see if it fixes it.
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