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Compression and Pump Gas

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Old Apr 25, 2011 | 02:26 PM
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Default Compression and Pump Gas
Is 11.5:1 compression to high to run 91 octane pump gas in the summer heat of Las Vegas?

I'm running 408 LQ4 block with stock LS3 heads.
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Old Apr 25, 2011 | 02:34 PM
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Thats getting pretty close, I',m 11.6 on 93, but i have an aluminum ls2 with stock cu.in.

For cruzing around i don't see an issue, but if you were to go racing i would put a gallon or 2 or 110 in there just to be safe.
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Old Apr 25, 2011 | 04:15 PM
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It will just be a daily driver but I'm worried about the 115 degree days in vegas.
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Old Apr 25, 2011 | 04:22 PM
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Set it to pull timing as the IAT's go up and you will be alright.
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Old Apr 25, 2011 | 04:40 PM
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if you're willing to pull timing you could run 13:1 compression on 91 oct haha.
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Old Apr 25, 2011 | 04:42 PM
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Originally Posted by s346k
if you're willing to pull timing you could run 13:1 compression on 91 oct haha.
The whole point of my question was can I run 11.5:1 without any knock retard.
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Old Apr 25, 2011 | 07:58 PM
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Originally Posted by oakley6575
The whole point of my question was can I run 11.5:1 without any knock retard.
A retard...you know like on Rainman It will be fine, just don't beat the **** out of it for exended periods of time when its that hot...
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Old Apr 25, 2011 | 08:05 PM
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It will completely depend on the valve events of the camshaft and the tune.
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Old Apr 25, 2011 | 09:41 PM
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Should be fine. Like the others said it comes down to a number of factors including heads and cam set up. With the elevation (and less dense atmosphere associated with it) you SHOULD be fine because the intake charge wont be as dense.
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Old Apr 26, 2011 | 08:31 AM
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Originally Posted by Beaflag VonRathburg
It will completely depend on the valve events of the camshaft and the tune.
This. I'm running 12:1 SCR and 8.7:1 DCR with 91 octane, but it takes careful parts selection and tuning.
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Old Apr 26, 2011 | 12:27 PM
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You can put a larger radiator in there and help keep it from pre-detonating . Good luck
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Old Apr 26, 2011 | 05:47 PM
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Originally Posted by Beaflag VonRathburg
It will completely depend on the valve events of the camshaft and the tune.
yup...static compression doesn't really mean anything...dcr is what you want to know...it takes the cam into account
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Old Apr 26, 2011 | 05:49 PM
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Originally Posted by chrs1313
yup...static compression doesn't really mean anything...dcr is what you want to know...it takes the cam into account
What DCR number do you keep it under to run 91 pump gas?
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Old Apr 26, 2011 | 05:58 PM
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Looks like my DCR is 8.40........ What does that mean?
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Old Apr 27, 2011 | 05:19 PM
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don't know about 91 oct...but I have pushed 9.0:1 on pump 93...some other things to take into consideration is the quench depth and how efficient the chamber is on the head...this will help lower knock too...
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Old Apr 27, 2011 | 05:25 PM
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Originally Posted by chrs1313
yup...static compression doesn't really mean anything...dcr is what you want to know...it takes the cam into account
It depends on more than DCR! Altitude and climate (density) play a HUGE part of this, and DCR ignores that.
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Old Apr 27, 2011 | 09:16 PM
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Originally Posted by Matt@Texas-Speed
It depends on more than DCR! Altitude and climate (density) play a HUGE part of this, and DCR ignores that.
well of course...also amount of timing, coolant temps, etc...

i was just saying for compression ratios dcr is better than scr...
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Old May 11, 2011 | 04:17 PM
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Can I run pump gas in 115 degree weather with a 8.40 dynamic comp ratio?
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