compression questions.

alex b · Post by **alex b** » November 6th, 2002, 3:20 pm

here in las vegas, most of the pumps carry 91 octane. the chevron i go to has 92. so what is the highest compression i could take my motor to with out detonation/knocking on 91/92 octane?

thanks.

Post by **Trey** » November 6th, 2002, 4:04 pm

I think a safe rule of thumb is 12:1 You might get away with more but with weather changes that margin will vary.

alex b · Post by **alex b** » November 6th, 2002, 4:40 pm

trey, man thanks so much. you're a well of knowledge.

Aj · Post by Aj » November 8th, 2002, 5:24 pm

The guys that I work with who came from Cali, and all the guys out at Jun that I've been fortunate enough to pick their brains, all said that they're running right about 12.3:1 compression.

They all told me, that if you're willing to screw with your timing when it gets closer to summer, then you could get away with like 12.5:1, just be careful about pinging.

I run 12.8:1 on 93 octane, but I also run my timing at 14 degrees, which is 2 degrees negative, though it still runs just fine, and fast as hell. Doesn't ping at all, unless I throw it a gear high under a lot of load, example: if I'm doing like twenty and aciddentaly throw it into 4th instead of second, and lay on the gas, then it'll ping a little, you just need to be careful.

Good luck, just remeber, it's better to run a little less compression, and not have to rebuild your motor, then get those couple of extra horses.

Later,
Aj

alex b · Post by **alex b** » November 8th, 2002, 9:00 pm

i was thinking the other night, and id like my compression to end up around 11:8:1 or so. i was thinking CTR pistons and a spoon headgasket would get me pretty close.

but of course if i could get away with 12:0 id probably go for it

Aj · Post by Aj » November 9th, 2002, 2:42 am

Actually CTR pistons and a spoon head gasket, correct me if I'm wrong would have you well into the High 12 compression ratio range.

Keep in mind, the Civic Type-R may have a compression ratio of 11.5:1, but by using the same pistons, that doesn't mean that yours will also, you need to take into account the wrist pin height......

Also, when using larger dome pistons, and a thinner head gasket, you may run into piston to valve clearance problems. I'd look into it a little more if I were you......

Also, if you're running 92 octane, I'd say your right, and to be on the conservative side you don't want any more then like 12:1. I'd say, go mill your head thirty thousandths, that would accomplish what you want, for very little money, and without you having to go into your bottom end. Just remember to back up your timing if it's pinging, and keep in mind it may offset where TDC on your cams is.

Good luck, later!!

Aj

alex b · Post by **alex b** » November 9th, 2002, 2:54 am

http://www.bseries.net/forum/viewtopic. ... 6a2d5b12ab

thats the only reason i thought it would put me around 11:8

dont worry i dont just throw anything in my R and hope it works, i research a lot of aspects, thats why any help you guys offer up is really appreciated.

-alex

2XS · Post by **2XS** » January 16th, 2003, 11:53 am

here is a spot that u can play with compression ratios with different internal mods
http://www.c-speedracing.com/howto/comp ... mpcalc.php

how much less should u run compression if u might regularly get caught on 91 octane?

JDMITR98 · Post by **JDMITR98** » February 24th, 2003, 7:21 pm

2XS wrote:here is a spot that u can play with compression ratios with different internal mods
http://www.c-speedracing.com/howto/comp ... mpcalc.php

how much less should u run compression if u might regularly get caught on 91 octane?

Hey thanks- that is really useful!

Aj · Post by Aj » February 24th, 2003, 10:01 pm

well, realistically, on 93 octane I run 12.8:1, and I have a couple close friends in Cali that run 12.2:1 on 91 octane, so I guess it depends on how conservative and safe you want to be. On on 91 octane to be on the safe side, I wouldn't run any higher than like 12:1 compression, maybe a tad higher, but keep in mind, the lower octane and higher compression, the more timing you need to back off.

In any case, good luck,
Aj

Aquafina · Post by **Aquafina** » March 6th, 2003, 9:09 pm

What would I have to do to be able to run 13:1 on a ITR motor stroked to 2.0L?

Aj · Post by Aj » March 7th, 2003, 12:10 am

Run 100 octane all the time. 12.8:1 is that fine line between race and pump gas, that your car will ping if it's really hot out side, especially without very good tunning and the correct fuel. 13:1 compression is just too high to run on pump gas, you basically at the very least will have to mix some race gas in with your 93 every time you fill up in order to keep from detonating. Not a smart idea, unless you have another car to drive.

AnY WaY,
Aj

ITRCA

compression questions.

compression questions.

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