L-82kid

Hello,

I'm about to rebuild my motor with higher compression and want to know what to run for gas. I had 9:1 comp.( w/flat tops and 76cc heads) and ran 89 octane without any problems. Now I'm running flat tops with 64cc heads (.041" gaskets), I think the compression will be around 10:1. I want to run high enough octane so I won't have any problems but I don't want to go broke everytime I fill up. I can get up to 94 octane near my house but I hope i can run 91 or 93 instead.

Thanks,
Kevin


[Modified by L-82kid, 11:26 PM 8/1/2003]

Shark Racer

Depends a lot on the cam too.

With iron heads, you MAY be able to run 91. 93 or 94 would be better.

With aluminum heads, 91 should not be a problem.

-Steve

Garson

I am running a 10-1 small block in my 74 with no problem with the premiem fuel. I live at 4000 feet and my timing is set for this alltitude. I will notice a little ping when I am at sea level when I lug the engine a little......

Garson

L-82kid

I have Iron heads and my cam is a Comp Cams ex268 (Adv dur. 268/280, @.050 224/230, lift .477/.480 LSA 110)

Thanks,
Kevin

GrandSportC3

you need premium - no doubt..

L-82kid

You guys think I can run 93 without any ping. This kid I know who has a built 5.0 mustang with 10.25:1 compression told me he needs 94 plus octane boost :crazy: . I hope I can stay with just pump gas.


Thanks,
Kevin

American Boy

I have 9.9 to 1 comp ratio with iron head and a roller cam XR-270 that has similar duration to your cam. I use 91 octane gas (they don't offer higher octane gas in Québec) and I have almost no pinging. I say almost because when the temp rise near 90 degrees, I hear some if I hammer it at low RPM. I probably need a different mecanical advance or metering rod to correct this. Other than that, it's all fine.

The secret was the quench of my engine or the distance between the top of the piston and the head at TDC. You have to deck the block to bring the piston flush with the block. After that, you put a 0.040" thick head gasket and you're done. It helps to keep away detonation by squishing the air fuel mixture to eliminate the leaner part of the mix. There's a lot of discussion about that in the forum archive.

Stephan


[Modified by American Boy, 2:47 PM 8/2/2003]

Matt Gruber

what is the deck height?
Some tips:
Block the heat riser.
Run cold air to carb.
Richen the carb if there is a ping problem.
Carefully adjust and tune the advance curve
Limit total advance.
since i run 9.65:1 with 87 and xe262 it should be OK with above tuning. :cheers: (91 octane)

L-82kid

My deck height is whatever came stock for the motor, I didn't machine the block at all. I'm doing just a top end rebuild, I'm going to keep the original L-82 crank and pistons. The motor only has around 60,000 miles and was taken care of and never raced. I just hope the original bottom end parts hold up to the new power.

As for the octane, even if i can get away with using 91 should i use 93 or 94 for more performance? Will the 2 or 3 difference in octane really make a difference in performance?

Thanks,
Kevin

Jvette73

On a Corvette, especially with performance mods, why skimp? Go high test all the way. A few extra pennys per gallon aint all that much. even in the owners manual of my 2001 minivan it says you can run what ever octane you want, but for improved performance they recomend high test. Im running flat tops with 64cc iron heads milled .012 and CCXE262. Im at least 10.5to1 probably closer to 11to1. With high test and a max agressive ignition timing curve ive never a single knock or ping.

stickboy

I have 10:1, iron heads and have no problems running 92 octane. I am actually trying 89 octane for a while to see if I can use it without pinging. With half 92 and half 89 I had no problems yesterday.

69stingray

Here is a website, I have not verified how accurate it is.

http://www.dunegoon.org/compression.html

Here is another one, this is the one I was looking for the first time:

http://www.turbofast.com.au/TFcomp.html


[Modified by 69stingray, 4:25 PM 8/3/2003]

L-82kid

Thanks for all the information guys, i think I will run 94 octane at first and then try and go down to 93 or 91 later.

Thanks,
Kevin