11.1 compression ratio and detonation
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11.1 compression ratio and detonation
Does anyone experience any detonation (and related timing retardation by the computer) with 11:1 comp ratios?
If so, is it only when the temp gets above 100 F.
I ask because I am just about to install AFR heads and 40 thou headgaskets on my 2001 C5 which will give 11:1 comp ratio.
I am told by several tuners in Australia, which is where I live, that this is very high for a two valve/cylinder engine and I may experience some problems with detonation. Hence, I may experience timing retardation well below peak power.
Octane rating will obviously effect this scenario. The octane rating in Aus is 98 RON, whereas it is 93 in the US (an average of the MON and the RON). I have been told that the two octane rating of the two fuels, i.e., 98 RON, and 93 (average of MON and RON) are equal,
Does anyone have any input/knowledge here please ?
I would prefer to not pull off the heads again and change back to standard head gaskets because of loss of power resulting from excessive retardation if possible.
If so, is it only when the temp gets above 100 F.
I ask because I am just about to install AFR heads and 40 thou headgaskets on my 2001 C5 which will give 11:1 comp ratio.
I am told by several tuners in Australia, which is where I live, that this is very high for a two valve/cylinder engine and I may experience some problems with detonation. Hence, I may experience timing retardation well below peak power.
Octane rating will obviously effect this scenario. The octane rating in Aus is 98 RON, whereas it is 93 in the US (an average of the MON and the RON). I have been told that the two octane rating of the two fuels, i.e., 98 RON, and 93 (average of MON and RON) are equal,
Does anyone have any input/knowledge here please ?
I would prefer to not pull off the heads again and change back to standard head gaskets because of loss of power resulting from excessive retardation if possible.
Burning Brakes
Joined: Sep 2004
Posts: 1,056
Likes: 0
From: Havelock, NC ( NJ Resident )
Originally Posted by russellnewnham
Does anyone experience any detonation (and related timing retardation by the computer) with 11:1 comp ratios?
If so, is it only when the temp gets above 100 F.
I ask because I am just about to install AFR heads and 40 thou headgaskets on my 2001 C5 which will give 11:1 comp ratio.
I am told by several tuners in Australia, which is where I live, that this is very high for a two valve/cylinder engine and I may experience some problems with detonation. Hence, I may experience timing retardation well below peak power.
Octane rating will obviously effect this scenario. The octane rating in Aus is 98 RON, whereas it is 93 in the US (an average of the MON and the RON). I have been told that the two octane rating of the two fuels, i.e., 98 RON, and 93 (average of MON and RON) are equal,
Does anyone have any input/knowledge here please ?
I would prefer to not pull off the heads again and change back to standard head gaskets because of loss of power resulting from excessive retardation if possible.
If so, is it only when the temp gets above 100 F.
I ask because I am just about to install AFR heads and 40 thou headgaskets on my 2001 C5 which will give 11:1 comp ratio.
I am told by several tuners in Australia, which is where I live, that this is very high for a two valve/cylinder engine and I may experience some problems with detonation. Hence, I may experience timing retardation well below peak power.
Octane rating will obviously effect this scenario. The octane rating in Aus is 98 RON, whereas it is 93 in the US (an average of the MON and the RON). I have been told that the two octane rating of the two fuels, i.e., 98 RON, and 93 (average of MON and RON) are equal,
Does anyone have any input/knowledge here please ?
I would prefer to not pull off the heads again and change back to standard head gaskets because of loss of power resulting from excessive retardation if possible.
Drifting
Joined: Oct 2004
Posts: 1,384
Likes: 8
From: Southwest Virginia
It will have a lot to do with your cam choice. If you have a fairly radical cam you can push higher static compression ratios before you get into trouble. I bought AFR 205 heads from LG that are cut .042 to 59cc and they swore I would not have any problems on 93 octane. I figured they have done enough to know, so I bought them! Now I just have to get the car on the road!
Safety Car
Joined: May 2000
Posts: 4,809
Likes: 344
From: Albuquerque NM
I'm running a milder cam (218/218, .561", 114) and higher CR: 11.4. It ran fine, no KR on 93 gas, now runs fine on 91 octane AT 5,000 ALTITUDE.
You should be OK. Modern design, fuel injected,Aluminum block/ high quench heads can run higher compression with less issues than in the past.
You should be OK. Modern design, fuel injected,Aluminum block/ high quench heads can run higher compression with less issues than in the past.
