I used to know how to figure it out, but it's been a long time since I've messed with engines. I have a stock 400 with the awesome 76cc heads, guessing comp ratio is around 8:1. If I put the Vortecs with 64cc's on it, what would the compression be on it?? Piston kits used to tell you what it would be with different CC heads, but can't find that info anymore.....
CK5
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76cc to 64cc compression ratio
- Thread starter b454rat
- Start date
mountainexplorer
1/2 ton status
The SB400 that I had was about 10.5:1 with flattop pistons and 041 casting 64cc chamber heads. If you still have the factory style dished pistons my guess may be like 9.5:1. But I'm no expert at calculations.
onlychevy6
1/2 ton status
You are pretty much dead on with that assumption. The piston will dictate what your true compression will be.
The motor is 100% stock. CR is around 8:1 on these, looked at a couple pistons and listed the ratios above. Now I need an intake. Anybody have one?? (cheap)
8:1 seems low for stock should be 8.5 at least.........I would believe it would raise about .8:1 for the 12cc in combustion chamber difference. Should give about 9.3 for the 4 valve relief style flattops
Not sure on the ratio, but I know in the 70s pretty much everything got low compression for emissions and crap. As long as it's under 10:1 so I can run pump gas with it.
Beast388
1/2 ton status
Just to give you an idea, if you have 9:1 comp. with 76cc heads, then you will have 10.25:1 with 64cc heads....all other variables remaining the same.
With 8.5:1 it would jump to 9.4:1 with 64cc heads.
There are quite a few more determining factors than piston shape when figuring compression ratio.
With 8.5:1 it would jump to 9.4:1 with 64cc heads.
There are quite a few more determining factors than piston shape when figuring compression ratio.
R77K10
Banned
as low as 8.0 Cr was very common, just look at the pontiac v-8s in the 70s alot of them were 8.0CR stock
im not sure on the 400 chevy engines, but they were probably not much more, if at all
make sure you srill the steam holes in the vortechs or whatever heads you use
good luck
im not sure on the 400 chevy engines, but they were probably not much more, if at all
make sure you srill the steam holes in the vortechs or whatever heads you use
good luck
