100 octane: is it good for miata? - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 12-10-2010, 03:26 PM   #21
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this is something we found in the early days of SSC. Lower octane made more power on a stock engine. The higher octane we were guessing took too long to burn. Leaving unused BTU's out the tail pipe.
This!
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Old 12-10-2010, 03:34 PM   #22
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I can believe the 'long burn', but if that were the case, couldn't you counter that by advancing the timing to put the cylinder pressure curve back where it belongs (peak pressure at 14deg ATDC IIRC)?
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Old 12-10-2010, 03:38 PM   #23
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Originally Posted by DammitBeavis View Post
I can believe the 'long burn', but if that were the case, couldn't you counter that by advancing the timing to put the cylinder pressure curve back where it belongs (peak pressure at 14deg ATDC IIRC)?
Yes you could. but then we're not talking about a STOCK running motor, which is what this thread is about.
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Old 12-10-2010, 03:59 PM   #24
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I can believe the 'long burn', but if that were the case, couldn't you counter that by advancing the timing to put the cylinder pressure curve back where it belongs (peak pressure at 14deg ATDC IIRC)?
Yes! This is pretty common for n/a guys, but for boosted guys this mean potentially more boost. The higher the octane the slower the fuel burns which give you more oportunity for HP, on the reverse side for a stock engine with you theoretically lose power as you are not releasing the same amount of energy from your combustion cycle.
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Old 12-10-2010, 04:40 PM   #25
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20 years ago, advancing the timing was possible on a stock engine.
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Old 12-10-2010, 04:40 PM   #26
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Originally Posted by DammitBeavis View Post
I can believe the 'long burn', but if that were the case, couldn't you counter that by advancing the timing to put the cylinder pressure curve back where it belongs (peak pressure at 14deg ATDC IIRC)?
you can, but why stop at just one gain?
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Old 12-10-2010, 04:57 PM   #27
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you can, but why stop at just one gain?
Huh?
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Old 12-10-2010, 05:01 PM   #28
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advance the timing and run 87
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Old 12-10-2010, 05:05 PM   #29
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I was assuming that it was already optimized for 87 and was simply pointing out how power loss could be minimized if the lower output from a higher octane fuel was related only to the burn speed and not the energy per unit volume of the fuel.

Edit: In addition it wouldn't matter on a stock engine anyway since you would need to massage the entire curve considering piston speed, and not just an overall change from moving triggers.
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