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gas milage? wrong hobby buddy
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Discussion Starter · #1 ·
getting ready to pick up a car from a friend and not sure what the comp. ratio is, has flat tops w/ valve relies i do know that much.with the heads off and the piston at top dead center, is there anyway to get a rough idea of what the comp. ration would be with a set of 64cc heads..
I.e.
.010 form deck would be= ?.? cr
.020. would be =?.? cr
ect...?

any help would be great guys... thanks in advance dan
 

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GXR11 said:
getting ready to pick up a car from a friend and not sure what the comp. ratio is, has flat tops w/ valve relies i do know that much.with the heads off and the piston at top dead center, is there anyway to get a rough idea of what the comp. ration would be with a set of 64cc heads..
I.e.
.010 form deck would be= ?.? cr
.020. would be =?.? cr
ect...?

any help would be great guys... thanks in advance dan
Could be between 8.5:1 to 11.5:1. There really is insufficient info given here to make an educated guess. With the head off, though, you can find out for sure what the compression is by taking all of the appropriate measurements.
 

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like 300 cubic inches or 500 cubic inches, bore stroke, engine make etc etc etc
8:1 to 11.5:1... is a good guess because it includes so many engines. That's funny though - enough information for any real guess :spank:
 

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gas milage? wrong hobby buddy
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52 Posts
Discussion Starter · #9 ·
hey guys , sorry for the lack of info. i was at work (not working obvously (sp?)) and rushed the question... and on the weekends i try to spend my time with my girl, not on my comp. she out on call for her job now(only reason im on here and not in bed with her now, lol) its a sbc 350 w/ .030 over. im sure you guys know the bore and stoke of these motors... im not even sure who made the slugs...yet. i gotta see if my boss still has any paper work from when the bottom end went together. im gonna be useing a set of dart heads i have(not the ones on the motor now) so the head gasket thickness is still an open matter until i see what i have as far as deck hight goes... if ya need any more info just ask... i'll be at work again in the AM... lol
 

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Just a guess.

I have seen sbc flat top pistons range from, 12 to 5cc. stock gm flat tops are 12cc and keith black hypers 2 relief being 5cc.

deck height is normally -0.020" (top of piston below the block), 4cc

most people use 0.040" felpro head gaskets. (sold at most local autopart stores), 8cc

and you know the heads are 64cc and the block is bored to 355cid (716cc/cylinder)

so with 12cc pistons
(716 + 64 + 8 + 4 + 12)/ ( 64 + 8 + 4 +12) = (716 + 88)/88 = 9.14

and with 5cc pistons
(716 + 64 + 8 + 4 + 5)/ ( 64 + 8 + 4 +5) = (716 + 81)/81 = 9.83

so if the piston has a -0.020" deck height, and you use a typical 0.040" felpro gasket and depending on the pistons, cr should be between 9.1 and 9.8.

could be 10.3:1 cr if the block was "0" decked with 5cc pistons or even 10.8:1 if a 0.020" head gasket is used with a 0 deck and the pistons.
 

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More for Less Racer
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[/QUOTE]10.8:1 if a 0.020" head gasket is used with a 0 deck and the pistons.[/QUOTE]


This bit of info is worthless because it won't run at these spec's without crashing the piston into the head. I've run at .034" total piston to head in a 7600 rpm 383 SBC and it just brushes the carbon on the piston. Anything under .030" clearance is asking for disaster. We are pushing it in a quest for compression ratio and we knew it would be very close from past experience.
 
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