454 block with 427 heads and intake? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-20-2010, 12:12 PM
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454 block with 427 heads and intake?

Hey guys, need some help from some chevy experts out there, I have a 1980 454 gmc engine that I am dropping into a 66 Vette I have been restoring. The guy I bought the engine from told me he had it rebuilt with a 427 cam installed in. I have bolted on the date correct 66 427 heads (3873858) and matching 66 intake along with a new Holley double pumper carb. I havenít tuned up the carb yet and I know the engine is running very rich but the engine seems to be laboring especially on the driverís side. Does anyone know if this combination of parts will work together or am I asking for trouble? Thanks

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Old 09-20-2010, 12:51 PM
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should be ok. both mark IV engines.

but use the 454 flywheel and balancer, as the 454 is externally balanced.

however, you could have a mismatch in compression ratio and cam shaft. we need more information to tell that.
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Old 09-20-2010, 01:18 PM
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If memory serves me right (its been 35 years)...there were open and closed chamber heads on the big blocks with pistons to match.......also, oval port and square port heads........I suspect a mismatch here.
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Old 09-20-2010, 01:57 PM
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3873858 heads are closed chambered heads, not the best set for performance! Open chambered heads flow 30% better then the closed ...I suppect thats part of your problem. ...Cam shouldn't be an issue.
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Old 09-20-2010, 03:02 PM
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thanks for the reply s,

both heads and intake are square ports so every thing lined up there and the heads are HP date correct for the car so i would like to use them. as for compression miss match, how would i go about figuring that out? and whould it cause the engine to run poorly. Any chance its just because the carb isnt tuned correctly yet?

thx
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Old 09-20-2010, 03:08 PM
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These are rectangular port heads, and need to have an intake that is also rec. port to match.

If that's how you are set up, find the p/n of the cam and/or the cam card for it. You may need to tune the carb and ignition curve to suit the combo, and know now that those heads- especially w/a radical cam- will want a loose converter and low rear gears.
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Old 09-20-2010, 03:11 PM
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I was typing while you were posting!

I have the chambers @ 109 cc. What pistons do you have? And are the heads milled? Block milled? You'll need to know that, as well as the head gasket thickness to pin down the CR.

What is the vacuum at idle?
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Old 09-20-2010, 03:29 PM
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a 1980 454 most likely has flat tops, so no clearance issues with open or closed chambers.

compression would be around 8.35:1 with flat tops and 109cc heads. This is good for a stock to mild rv type cam. or good for a boosted engine (turbo, blower, super charger, n02...)

you could run a "big" cam with this compression but power would be reduced, especially in the low rpms.

what is the ignition timing at idle, total mechanical advance, added vacuum advance?
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