Thread: compression ratio calculators

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i'm trying to figure what i'm running for a compression ratio...
i tried many compression ratio calculators and there pretty much the same......there saying i'm running 11:1ish and i cant see it....
so if anyone can help me with some numbers to make sure there correct... its a stock bore 350 and stock deck height..., double bump heads milled down to 60cc and the head gasket that comes in the felpro top end gasket kit and it has the truck pistons that are dished with 4 valve reliefs...

bore size 4(stock?)
stroke 3.48?(stock)
head gasket bore ?
head gasket thickness .030??
combustion cahmber 60cc
dome or dish volume -.100???
piston deck clearence .025?

can some tell me if this is corect or correct me...

cylinder 717 cc's
chamber 60 cc's
gasket 8 cc's
deck 1.6 cc's
piston 7 cc's
all added together 793.6 cc's
add together chamber, gasket, deck and piston 76.6 cc's
divide 793.6 by 76.6 = 10.36:1

gasket, deck and pistons are educated guess.

i really appreciate the help guys i was getting different answers from everyone i talked to.. 10:36 thats more than i thaught i was running i guess thats why it works well....i'm gonna do a compression check when i get it out this spring to make sure everythings good....whats a good base line...i know its more inportant that there even and cam and other things will affect the reading but whats ok and and what should make me worry???
the motor was rebuilt but the pistons were re-ringed cause apparently the cyclinders were ok...

it was rebuilt 2 yrs ago

thats a great chart u hit the nail on the head..is it best hot or cold to get an accurate read??

My ol' 390 runs 150 on all holes warm.

Thanks for the chart Denny.

just checked one cyclinder for now, the garage is full of cars... 150+ the gauge was bleeding down when i got to it so its probably 155ish that make me feel a little better

that cam must give me some leway cause i had to use mid grade gas a couple of times in a bind and no ping unless i got into it...i try to run the good stuff...

Part Number: 110551 Grind Number: H-228/320-6
Engine Identification:
Start Yr. End Yr. Make Cyl Description
1957 1987 CHEVROLET 8 PERFORMANCE USAGE, GOOD MID-RANGE TORQUE AND HP, BRACKET RACING; STREET, HEAVY, ETC., AUTO TRANS W/3000+ CONVERTER, 9.5 TO 11.5 COMPRESSION RATIO ADVISED. BASIC RPM 2800-5800
Engine Size Configuration
262-400 C.I. V

Valve Setting: Intake .000 Exhaust .000 HOT

Lift: Intake @Cam 320 @Valve 480 All Lifts are based
on zero lash and theoretical rocker arm ratios.
Exhaust @ Cam 320 @Valve 480
Rocker Arm Ratio 1.5

Cam Timing: TAPPET @.004
Lift: Opens Closes ADV Duration
Intake 36 BTDC 68 ABDC 284 °
Exhaust 68 BBDC 36 ATDC 284 °

Spring Requirements: Triple Dual Outer Inner
Part Number 96802
Loads Closed 107 LBS @ 1.800 or 1 13/16
Open 284 LBS @ 1.340
Recommended RPM range with matching components
Minimum RPM 2800
Maximum RPM 6400
Valve Float 7000

Cam Timing: TAPPET @.050
Lift: Opens Closes Max Lift Duration
Intake 12 BTDC 36 ABDC 102 228 °
Exhaust 44 BBDC 4 ATDC 110 228 °

it pulls like hell as it hits 3 grand.. it sounds great when it wants to idle.. it kinda goes off on its own then come back to the rythm... under a load it'll stay steady but thats kinda hard to do with a stick...lol i may run a hotter plug just running the AC's rapid fires in the cr43ts heat range..i find they work well but foul really easily so i may be changing them...i tried leaning air mixture screws but the plugs are still on the black side making me think thats why it wont idle right...it seems to work great down the road but idleing its very stubborn...i'm running a afb competition series... i looked at the new barry grant carbs(demon)and i like the air screws built in to adjust for a lumpy cam easily....any suggestions??

another question that may be cleared up on the cam spec card which duration would i be running??? i see a 228 and 284...i know u can retard or advance the cam by timming marks on cam gears is that what that means??? mines right on not advanced or retarded

The main thing you're doing when you advance or retard the cam is changing the intake valve closing point relative to crank position. When you advance the cam, you close the intake valve earlier, trapping more fuel/air mixture as the piston rises on the compression stroke and making more low end torque. Retarding the cam will soften the bottom end while adding more poop to the top end.