compression ratio

Reply Subscribe

Thread Tools

Search this Thread

Feb 25, 2006 | 10:26 PM

Powergod

Thread Starter

Junior User

Joined: Feb 2004

Posts: 70

Likes: 0

From: Illinois

compression ratio

I am rebuilding soon and I am wondering what the highest ratio you would do on 93 octane. I would like to get to 12:1 or 12.5:1. i think I would need more than 93 octane but not sure. If so does octane booster and 93 gas work? Thanks.

Feb 26, 2006 | 01:32 AM

DeanG

Junior User

Joined: Apr 2003

Posts: 88

Likes: 0

I'm running 10:1 compression with D2OE iron heads, block decked, and a Crane street/strip dist that has variable timing curves. I am running right on the hairy edge of detonation with some of the curves, and others I can't even think about using in a truck. Even with aluminum heads I doubt you could get away with 12:1 compression on 93 octane. I doubt aftermarket octane boosters would help you much either. How much comp you can run with pump gas depends on how your engine is set up and what kind of loads you expect to put on it.

Feb 26, 2006 | 02:07 AM

ivanribic

Post Fiend

Joined: Jul 2003

Posts: 11,945

Likes: 3

From: Spokane, WA

My new build is 10.8:1 with aluminum heads and I'm pushing it at 93 octane. You don't want anything over 11:1 for premium pump gas and that's WITH aluminum heads. Because of the thermal properties of aluminum vs iron you can run higher compression with aluminum heads. From what I've seen 10.5 seems to be about the limit for pump gas with iron heads.

Octane boosters really don't boost octane that much. When you read the bottle and they talk about boosting "points" the points are not octane numbers, they're fractions of octane numbers. So when it says it will raise octane 3 points you're not going from 93 octane to 96, you're goind from 93 octane to 93.3 octane . . . a slight increase but nothing that will allow you to run 12:1 compression.

Feb 26, 2006 | 08:32 AM

Powergod

Thread Starter

Junior User

Joined: Feb 2004

Posts: 70

Likes: 0

From: Illinois

Well this is for a pull truck. I have to keep iron heads for my class. I will be running it hard. I will be going with a full roller set-up with about 680 lift, I can't remember the exact specs. I am hoping to get to about 6800-7000 rpm's. What octane is needed for 12:1? about 100 or 104? What about a mix of 93 and 104? This is not a dailey driver. Thanks again.

Feb 26, 2006 | 09:28 AM

frederic

Post Fiend

Joined: Oct 2003

Posts: 6,214

Likes: 13

From: New Jersey

or 12:1 I'd use race gas exclusively, in a puller. Any noticable detonation in a 12:1 engine will result in broken parts.

Feb 26, 2006 | 12:05 PM

monsterbaby

Hotshot

Joined: Dec 2003

Posts: 18,423

Likes: 9

From: iowa

at 12:1 with iron heads, and some very carefull tuning you could maybe get away with 100LL av gas, dependant on the entire setup, but in pulling, or racing you don't want to be running on the ragged edge of your octane requirements so I would recommend running 110 min. I am at 13.5:1 with alum heads and can run 110 (figure you can get away with about 1 full point of compression with the same octane with alum VS Iron heads) I am not seeing any signs of detonation so you could go to 12.5-12.8:1 with 110 octane pretty easily but even with mine I am stepping up to atleast 112 octane and possibly 114 for this year.

Feb 26, 2006 | 06:30 PM

Powergod

Thread Starter

Junior User

Joined: Feb 2004

Posts: 70

Likes: 0

From: Illinois

so, I guess if I am going to go with 12:1, I am going to need race gas with at least 110 octane. 110 will be ok for 12:1 correct. Where do you guys get 110 gas? I don't know of any places around me to get any.