Octane

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Rmoore

Rmoore

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Whats the highest compression any of y'all have ran on a street/strip 512 cubic inch motor that didn't have any spark knock or tear up some pistons.. 10.5 to 11.1 is what you read about with 93 octane !!
 
I think that with aluminum heads that 10 to 1 on 93 gas is the base. That is what I use and have not had any problems, since gas is changing all the time.
 
You may have better gas than we do here in the mid west, the better the gas the better it will run. It is hard finding even 93 here, and all the additives, who know what.
 
Argh! Just build it really safe. Don't try to squeeze every last horsepower out of it.
 
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My small block 416 with Edelbrock heads had 11.9 to 1 compression ran just fine on 93 octane..
 
stroked340 said:
My small block 416 with Edelbrock heads had 11.9 to 1 compression ran just fine on 93 octane..
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LSA on your cam make a difference as well. Lots of thing involved really. I was just wondering what most hot rodders ran on the streets. I know some guys that run 14 and 15 to 1 on streets. They just run races fuel. Obvisiously they have more money than I lol !!
 
Rmoore said:
Whats the highest compression any of y'all have ran on a street/strip 512 cubic inch motor that didn't have any spark knock or tear up some pistons.. 10.5 to 11.1 is what you read about with 93 octane !!
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My 511 is 11.24:1 and runs on MI 93 pump gas no problem.No signs of detonation anywhere. Cam is 270*@50 with a 110* LDA. Not much to gain going as far as 12:1, maybe 2hp, so keep it in the lower 11's. You would have to go to 13- 14:1 to reap any good benefitts of more hp. not really worth it as race gas is very expensive.
 
Look at you cylinder pressure. If you run 12.1 and still have 200 PSI on each cylinder, you can run pump gas 92-93 as long as it run ok and your not racing it. 200 psi is about the limit. I tried it on my one motors that is 12.4 and had no problems, now if you are going to race, I would put race fuel in. Or you could go 50/50 on your fuel mix for the street.
 
10.8. .035" quench. I agree with the above posters though... No reason to push limits nowadays.
 
moper said:
10.8. .035" quench. I agree with the above posters though... No reason to push limits nowadays.
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What timing are u guys running w/ 91 octane , in 505-512 strokers ?
initial / total? all in by ??
 
famous bob said:
What timing are u guys running w/ 91 octane , in 505-512 strokers ?
initial / total? all in by ??
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My cam has a 270*@50 duration, so i have my timing at 28* initial and all in at 2800rpm at 34* total. I ran it locked out for awhile and still had no detonation issues locked at 36*.
 
Do you have any hot-starting issues at 28 initial? I've got my 451 (with a 272 @ .050) at 22 and it's on the edge of kicking back...
 
It was a customer's, who since sold the car. It goes back some years but - IIRC it was around 16* initial, and 30* total. Car was a stick with 3.54s and a stick so it came in around 2500. Had a six pack on it and he ran pump 93 w/10% ethanol. No issues aside from way too much power.
 
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bluefish said:
My cam has a 270*@50 duration, so i have my timing at 28* initial and all in at 2800rpm at 34* total. I ran it locked out for awhile and still had no detonation issues locked at 36*.
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Locked at 36* hot was sometimes an issue starting. 28* no problems, but I do have a 10* start retard in my Ice Ignition box.
 
I ran 13.5 to 1 in my 451 a few years ago. I am at 5400 feet so that's like 12.5 at sea level. Started with ported 906 heads at 12 to 1, and it would run mid 13s on the 1/4 mile.Went to ported 915s and headers, with .037 quench. Then it ran 12.40s. So the 1.5 boost in compression and headers with good quench was worth a full second. Ran 20 initial, 38 total on timing. 88 main jets all around in the 850 Holley. It would ping, but if I ran a 50 50 mix of 91 premium with 100 race gas, then it ran fine. The premium up here is only 91 octane. Best running street strip motor I ever had.
 
Cranking compression on the 451 was 210 to 220 PSI. I used the 509 cam, which worked great. The relatively late closing point of the intake valve, helped keep cylinder pressures from getting too high at lower RPMs. That is where it was more likely to Ping. It had great torque from about 1800 RPM and up.
 
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