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Originally posted by 50DADDY:
Ive always believed that runing more octane than needed in a car can slow it down.When i first started racing i had a lower compression motor in my car(8 something to 1).Being new to racing i would put 91 octane(even race gas once)in it thinking i would go faster.What actually happened was i lost a touch of et and mph.Higher octane means it is harder to ignite/burns slower or less violently right?So my thinking was that since i didnt have high compression or issues with detonation the high octane wasnt needed.Since the lower octane burns faster and hotter it made more power with my particular setup.From then on ive always subscribed to this theory and laugh when people waste money on high octane fuel in theyre stock 5.0's.Is this true though?Anyone else experience this?Was i imagining shit?LOL!

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Originally posted by nitrous_bob:
to make optimum power you want to be on the RAGGED edge of lean

but you need to know your car to stay safe

yes....ABSOLUTELY more unneeded octane will slow you down....just like overkill closed plugs, and colder plugs than needed

octane reduces combustability, thats why it reduces detonation

a car runs better with more octane NOT beacuse of it....but IN SPITE of it if you get what im saying

your not fixing an issue, your feeding it i guess

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Just what i thought.
Alot of people need to read this post,lol.
 

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Posted by racsirx (Member # 1710) on :
 
I couldn't see running low octane with advanced timing on a stock Foxbody, but my all stock 95 with stock timing will ping like crazy if I don't run 91, I like to maximize timing when racing and I couldn't see doing that without race gas. 20 years ago I think we were setting the initial timing 18-22 degrees with 100-110 octane to get a stock Mustang in the 12s but I could be wrong since it was a long time ago but it was something like that. But on a basic 500hp +/- blower car, Foxbody, I couldn't see going over 110 octane with 24-26 total timing, and a turbo car, Foxbody 500HP+/-, 117 octane works very well with 24-26 total timing.
 

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Posted by MaK_1967v8 (Member # 12187) on :
 
my 67 mustang pings & sputters running 87 octane. on 91, it runs like a champ.

I have a 289 w/ 302 heads. unknown cam, 600 cfm edelbrock carb. timing is set at 12. ( tried retarding it to 8, but it sputtered and backfired out of the carburetor )
 

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Posted by SteveL (Member # 1241) on :
 

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Originally posted by racsirx:
I like to maximize timing when racing and I couldn't see doing that without race gas.

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Originally posted by SteveL:

quote:

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Originally posted by racsirx:
I like to maximize timing when racing and I couldn't see doing that without race gas.

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Try reducing the timing. It's easier to see if you're improving while on a dyno. To get the maximum power, you want the maximum explosion from the air/fuel mix burning just after TDC. Higher octane burns slower so you need to advance the timing to get that max explosion with the piston in the right position (just after TDC). Lower octane burns faster so the spark can start later and still make the same and possibly more torque. You'll get more power (torque) when the max explosion (really called peak cylinder pressure) when the piston is near the top of the cylinder and just on its' way down.

If the engine pings, it doesn't automatically mean you need higher octane. You may have the spark too far advanced. Advance the timing too much and the peak explosion occurs right at or a little before TDC which will ping.

My point is higher octane and advanced timing by themselves does not make more power. You really need to try different combinations to see what works best in your motor.

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