NINJA12
Needs a job
Posts: 3310
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posted December 17, 2001 06:03 PM
octane requirement with 12:1 motor
My buddy just built a small block chevy 350.
12:1 piston, street comp cam. with headwork.
He says he must run 93 with booster at all times.
He also thinks it will loose massive power if he runs straight 93 and lower his timing.
Is he right?
I don't think so.
  
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silver01bullit
Expert Class
on here too much
Posts: 333
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posted December 17, 2001 07:20 PM
I think it depends on how the combustion chamber is shaped along with dome volume on the piston, etc. The 12 doesn't need (IMO) octane booster. I ran some of that shit and ended up with carbon deposits on the back of the valves and it ran like shit. Your friend maybe right but it depends how streetable he built that motor. He may have some huge domes on those pistons (needing octane booster) or he may have some very small domes and very small combustion chambers. Higher octane isn't always the answer, depends on the setup.
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dougmeyer
Needs a job
moderated
Posts: 2713
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posted December 17, 2001 09:20 PM
HE needs it, YOU don't. He's absolutely right.
Small block Chev is a wedge combustion chamber, definitely needs at least 92 unless you kick the timing back below about 36 deg total. And, yes he'll feel the power loss with that. What kind of ignition and fuel delivery has a lot to do with it. If it's carbureted with a basic ignition (CDI, no computer) this is especially so. EFI will make it a lot more manageable.
Your bike has a very flat, high turbulence combustion chamber and is very detonation resistant, The good news for your buddy is taht the detonation (ping) is very audible and he can recognize and avoid it. (if he's smart)
Doug
____________
It's not that I think you're dumb, it's just that so much of what you know isn't true....
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NINJA12
Needs a job
Posts: 3310
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posted December 18, 2001 10:33 PM
Thanks everyone.
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