i just purchased a new 350 crate motor from GM. its a stock 350 not a performance one or anything and i bout a Edelbrock performer EPS intake and a Edelbrock performer 600 cfm carb to go with it. my question is about the restrictor plate that goes on the center port of the intake manifold gasket. in the instructions it has a chart for different year vehicles and stuff but i don't know what i would use for my new engine. it will have headers on it not the stock manifolds if that makes a difference. thanks for any help.
those are block off plates for the exhaust port that runs under the intake for faster warmups on cold mornings---it also heats the intake and vaporises any raw gasoline that would otherwise puddle under the carb. its your choice whether to use them or not---there are benefits on both sides of the decision
PROS for leaving them out---- faster warnups and slightly better economy
Pros for putting them in-------better performance
just my opinion................Dan
My son is renovating a 74... Living in Florida means not too many cold mornings, hes installing a new manifold & carb per above... a mechanic advised to leave the port blocked off? I.e. do not even use restrictor plate, stating that this would improve the performance? Im guessing by keeping manifold from heating up? emissions controls have been removed... Input welcome guys as son is dying to get installed...
Usually there are an assortment of restrictor plates (namely rectangular pieces fitting the passage with different size holes) in this 1st generation SBC intake gasket kits. The idea being the bigger the hole, the more exhaust gas and heat flows under the intake manifold. Having a little heat in this area is a good thing when it prevents atomized fuel from dropping out of the air-fuel mixture. Raw fuel that can accumulate will also be evaporated and used by the motor. Trouble is too much heat may give you heat sink problems on restarts after warm.
Conclusion (for Florida): block the exhaust passage off (or, if you must, use the restrictor plates with the tiniest holes).
One last issue with these exhaust passages is the build-up of crud, gunk and burnt oil. These exhaust passages are often blocked by carbon in the form of burnt oil (AKA "coking" - kind of looks like black scrambled eggs). Burnt oil should be avoided for obvious reasons and is an excellent reason to never run these exhaust passages without some type of restrictor plate. I have attached a photo of a typical SBC 1st generation intake gasket with sheet metal restrictor plates.
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That is great information thank you, you are right about the carbon build up, it was present when he pulled the old manifold off & the restrictor plates were previously used... The gasket has a removable section, I.e. it is blocked off, and the plates you show... If I understand you correctly we should leave the gasket blocked off, or we could remove & add a restrictor plate... Thanks again... My son James is loving his project...
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