Highest Compression on Pump Gas

[BoosterSH]

Anyone know on pump (93 octane) gas the highest compression that can be used before experiencing detonation? Assuming proper air/fuel mixture.

:bandit:

[ivymike1031]

there really are LOTS of factors that go into answering that question (carbon buildup inside cyls, vol. eff. at running point, more that I know of but can't remember, and many more that I've never known), so I don't think anyone will be able to give you an accurate answer off the top of her head (barring lucky guesses).

[ivymike1031]

to illustrate the point, I'll give an example -

there's a gasoline engine, under development by a major US OEM, which has a static compression ratio of 12.3:1 and runs on 87 octane fuel.

Prior to seeing the design (and knowing people involved in the testing of it), I would have laughed if someone had suggested that was possible.

[BoosterSH]

Well the reason was because im planning several things for my car. Im either going to build an all-motor application or run some boost. If i decide to go all motor i plan on raising my compression to about 12:1, running the car on 93 octane. The whole engine (block, pistons ect) will be removed, cleaned or replaced with aftermarket parts.

Thanks for the info thou!

[drift]

static compression on pump gas peaks normally at 11:1 - 12:1. you can get away with 12:1 or higher safely with a redesigned head quench area to maximize fuel swirl within the combustion chamber. your cams and ignition can also be timed to reduce dynamic compression to further prevent detonation.

H22A motors also feature a knock sensor. once knock is detected, the motor's ignition is retarded and fuel is added automatically to prevent detonation. this can help you play it a bit safe during initial tuning, but it's scope of effectiveness is only so much, as it can only make adjustments AFTER something has happened.

[97teg]

i've heard don't go above 11.5:1

[civicx_xracer]

Originally posted by ivymike1031
to illustrate the point, I'll give an example -

there's a gasoline engine, under development by a major US OEM, which has a static compression ratio of 12.3:1 and runs on 87 octane fuel.

Prior to seeing the design (and knowing people involved in the testing of it), I would have laughed if someone had suggested that was possible.

All I have to say is Who is making this. Where did you find out about this?? As far as answering the ? itself in a general aspect you should be ok on 93 as long as everything is tuned and set properly but for racing I wouldn't recommend anything less then 98

[ivymike1031]

"A major US oem" (can't tell you - client confidentiality), and "at work." If you're patient, you'll probably see it in dealers' lots in about 1.5 years.

[threethirteen]

12.3:1?? damn..imagine the possibilities of raising that and giving it 93 octane...you could raise your compression to like 14:1...and still run pump gas... or you could lower it to like 9.5:1 and feed it 20psi and still use 89 octane...

hmm...

thats gonna be one hella engine

[ivymike1031]

Actually, it's going to have a pretty meager output considering its displacement - ~150hp out of a little over 2L. It's intended to be a high efficiency engine (hence the high compression ratio).