What is the highest compression ratio pistons anybody has run and what was the final compression ratio when everything was put back together. This might be asking a lot but try to include what design the pistons were, if they were coated with something, how far up the piston the first ring was, what the piston was made out of, what rings you used, how much the deck was milled, how much of the chamber was bored, what size the head gasket was and what the heads were.
Also what if any problems did you have with detonation. I know the detonation problems will vary between the engine sizes, so what size was the engine? Thanks.

Tibo

 

12.5:1 domed or "pop up" 2 valve reliefs, uncoated, no idea on ring groove location, zero deck, never heard of boring the chamber must be something new, no idea on head gasket, iron chevy heads, 092s i think, no problems with detnation

 

not my own car
but something I read
12:1 on 87 octane
no stats right now

 

.060" over flat tops in a 350 with 52cc heads .015" deck clearance
thin .015" head gasket 5cc valve reliefs... Big solid dirt cam.

12.65:1 compression ,,,,,ran like a raped ape for a while on 94octane but eventually succomed to high speed detonation and broke a ring land. Never heard pinging.

 

So it sounds like 12.65 is as high as one could go on 93 octane pump gas? Good to hear that people are running 12:1 CR and not coming across detonation problems. I started the thread because I am looking at 10:1 flat top or 11:1 Pop-ups. Thanks a lot.

 

Chevy HiPerformance Magazine had a recent article on detonation. Apparently on a scale of 1 to 10, audible detonation begins at about 9. Detonation is still occuring at the lower levels and still causing damage but you won't hear it. Scary!

 

You guys are overlooking one big additional factor in all of this discussion regarding compression ratio. Camshafts with longer duration periods and greater amounts of overlap can tolerate higher static compression ratios because the different cam timing lowers the dynamic compression ratio. Reducing the dynamic compression ratio is what keeps the engine from suffering damage.

If you had a bone-stock cam in an engine and did nothing but increase the static compression ratio (via flat-top pistons and small chamber heads, for example) you would quickly run into trouble with pinging and detonation. However, the same static compression ratio in an engine outfitted with a longer duration camshaft may be just fine.

The question you need to be asking these folks should be more like: what was your highest compression ratio you ran, and what sort of camshaft did you use with it?

Camshafts with longer duration periods and greater amounts of overlap require increased static compression in order to work best.

 

Good thinking! I'll use your question. Now on with the responses.

 

Camshafts with longer duration periods and greater amounts of overlap require increased static compression in order to work best.

Thats true.... but with that higher compression ratio
you'll need more octane to avoid detonation.

Compression is compression reguardless of what cam is in the motor.

the "dynamic compression" will have a minor effect on the real octane requirement of a motor, at best.
Were talking 1/2 to 3/4 of a compression ratio difference.

A cam that is too big and spits usable cylinder pressure out the exhaust pipe (over scavageing) instead of using it to push on the piston and make power is a waste.

Actual net gain 0

 

i never ran pump gas. if i were to build another preformance engine i'd use the highest compression dished pistons i could find along with the smallest chamber heads, but like i said before i don't know much and that's just an idea i've had for a while