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Join Date: Aug 2011
Location: Royal Oak, Michigan
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dumb question on max compression ratio

Good evening Pelican

What is the highest CR on a single plug with pump gas?


Thank you


David
Old 06-12-2018, 04:02 PM
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Location: behind the redwood curtain, (humboldt county) california
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It Depends...

Fuel octane ratings vary. here in kalifoania, 92 is about it and that is with alcohol. We cannot buy "pure" gas unless we swear a blood oath, in writing, that such criminal fuel will NEVER be used on the highway.

did someone get bought off on that one???

To a lesser extent, it depends on the cam duration, overlap and the ability of the engine to go over 100% volumetric efficiency, (dynamic compression).

Still pissed off,
chris
Old 06-12-2018, 05:54 PM
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10:1
Old 06-12-2018, 06:39 PM
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10.5:1 with carbs and, most importantly, S + cams. The overlap reduces the dynamic compression. Single plug.
In MI, you may be able to get away with milder cams. My euro 3.0 has SC equivalent cams stock and 9.8:1 stock, pump gas, single plug.
Old 06-12-2018, 07:57 PM
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I'm still on the fence weather I want carbs or ITB. I have absolutely no idea about what Cams I want other than I have no intention on racing so nothing too aggressive.

Thanks

David
Old 06-13-2018, 02:53 AM
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Quote:
Originally Posted by Harpo View Post
I'm still on the fence weather I want carbs or ITB. I have absolutely no idea about what Cams I want other than I have no intention on racing so nothing too aggressive.

Thanks

David
Well tuned carbs vs well tuned ITB / EFI:

https://www.youtube.com/watch?v=aj-Z33MO2Gk

Quite interesting.
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911 Silver Targa -77, 3.2 -84 with custom ITBs and EFI
911T Coupe -69, 3.6, G50, "RSR", track day.
Old 06-13-2018, 06:13 AM
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