 Engine Modified: What is the highest compression for 93 Octane?, engine mods, compression, 93 octane |
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| Stark 01 |
 Aug 28 2015, 10:54 AM
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#1
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Racing newbie  Group: Members Posts: 43 Joined: 26-May 14 From: Concord, NC Member No.: 17,404 Region Association: South East States  |
Hi everyone,
Those of you who have built up a Type IV 2.0 with higher compression, what is the safest compression ratio to use 93 octane pump gas? |
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| RoadGlue |
Aug 28 2015, 11:57 AM
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#2
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Sonoma County Gear Head Group: Admin Posts: 2,033 Joined: 8-January 03 From: Santa Rosa, CA Member No.: 108 Region Association: Northern California 
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This question invokes a bunch of other questions.
- Stock cooling or are you running a front-mounted oil cooler too with thermostat, etc? - Stock P&Cs? Deck height can be an issue... - Stock 2.0 heads? - Stock cam? Higher compression = more heat. |
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| Stark 01 |
Aug 28 2015, 12:11 PM
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#3
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Racing newbie Group: Members Posts: 43 Joined: 26-May 14 From: Concord, NC Member No.: 17,404 Region Association: South East States |
QUOTE(RoadGlue @ Aug 28 2015, 01:57 PM)  This question invokes a bunch of other questions. - Stock cooling or are you running a front-mounted oil cooler too with thermostat, etc? - Stock P&Cs? Deck height can be an issue... - Stock 2.0 heads? - Stock cam? Higher compression = more heat. -- Stock cooling or are you running a front-mounted oil cooler too with thermostat, etc? Ans: stock cooling for now, but am considering front-mount. It is my understanding that I will need to know which before building the engine so I can stub in the external cooler lines, yes? I have a used one in my shed, but I don't know it's history. - Stock P&Cs? Deck height can be an issue... - Stock 2.0 heads? Ans: bored over and forged pistons. Will have to find out what has been done to the heads. - Stock cam? Ans: No. |
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| Dtjaden |
Aug 28 2015, 12:25 PM
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#4
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Member Group: Members Posts: 232 Joined: 25-May 13 From: Morgan Hill, CA Member No.: 15,915 Region Association: Northern California |
I'm running a 2056cc engine with a Web Cam #86 camshaft. I also have a rear trunk mounted oil cooler. My CR is about 9.2:1. I use a Megasquirt engine management system. On CA 92 octane gas I have had no problem with detonation.
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| toolguy |
Aug 28 2015, 02:32 PM
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#5
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Senior Member Group: Members Posts: 1,267 Joined: 2-April 11 From: San Diego / El Cajon Member No.: 12,889 Region Association: Southern California
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Forget about piston compression ratio. . which does not take into account ignition timing, cam design, cam / valve timing, lobe overlap and separation, all of which reduce maximum designed piston compression ratio. .
Take a compression reading and see where the motor actually is. . anything around 160-175 is still pump gas. 150 or lower is definitely regular gas. Modern engines can run lower octane, but remember they have ECU's with sensors and do all sorts of magic to get reliability and mileage on cheap gas. My 69 Z-28 had 220 psi , factory rated at 11:1 compression, and wanted 98 or better back in the good old white pump Chevron days. 9.5 : 1 should be good on premium gas these days. |
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| yeahmag |
Aug 28 2015, 06:06 PM
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#6
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Advanced Member Group: Members Posts: 2,421 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California
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I strongly disagree with the above. Go with the CR that your cam dictates unless you know what you are doing. I've built more than my fair share of motors at this point and I still tend to fall within those CR numbers. While all those variables do change what static CR you can run, all the cams I run (WebCam) come with a recommended CR stated.
Deck height, displacement, and head CC will dictate CR. |
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| Dave_Darling |
Aug 28 2015, 06:23 PM
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#7
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914 Idiot Group: Members Posts: 14,981 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California
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Yup, unless you are really significantly changing the design of the combustion chamber and adding lots of sophisticated sensors, the cam has the single largest effect on what compression ratio is appropriate.
--DD |
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