Figuring out compression ratio

HoleshotKFX400 · May 13, 2008

Does anyone know how to figure out compression ratio without ripping all kinds off stuff apart... like a easy way? When I bought my motor I bought it from my buddys dad... his son had built it but passed away but he didnt know all the specs on it. I was told i have to run race gas but I have no clue how high of octane or anything... It would be nice if i could figure out my compression but i dont know the headgasket thickness or what pistons are in it? or how much was shaved off the heads... Im running CAM2 110 right now to be on the safe side but if i could run lower i will, this stuff is killing me @ $7.90 a gallon

v-8power · May 14, 2008

Try running a small amount of lower octane fuel through it, see how it does.

Totalled · May 14, 2008

Kinda hard without CCing the heads and piston to deck clearance... You might be able to get an idea with cranking compression.. unless it has a big cam with lots of overlap.

HoleshotKFX400 · May 14, 2008

what do you mean by cranking compression? what a compression checker reads?

HoleshotKFX400 · May 14, 2008

It has a Edelbrock Performer RPM

Duration at 0.050" Lift: Intake: 224° Exhaust: 234°
Lift at Valve: Intake: 0.496" Exhaust: 0.520"
Timing at 0.050" lift: Open Close
Intake: 5° BTDC 39° ABDC
Exhaust: 54° BBDC 0° ATDC
Centerlines: Lobe Separation - 112° Intake Centerline - 107°

stranger · May 15, 2008

judging from the parts discription in sig.if flattop pistons and guessing on mill of heads not knowing head cc(figering 56cc) i would guess 11-11.5:1.you will never know without teardown.
octane used and external compression will not tell you.run premium and the most timming you can.then call it good

HoleshotKFX400 · May 15, 2008

Alright thanks guys, I guess ill mark the dist where i have it at now for the race gas, then as soon as i run it out... ill get some 93 and see what i can do with that...

baddad457 · May 17, 2008

With 54 cc 289 heads and zero deck flat tops, the highest it'll have is 10.5 to 1. With shorter pistons ( pin heights run from 1.585 to 1.615) it can be as low as 9.5 to 1. Only with pop up pistons will it have more. Fill it with 93 octane, set the timing to 12* BTDC and see what it does.

Figuring out compression ratio

HoleshotKFX400

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v-8power

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Totalled

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HoleshotKFX400

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HoleshotKFX400

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stranger

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HoleshotKFX400

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baddad457

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