What is the best way to increase CR?
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Cruiser
Joined: Jul 2006
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From: Andover, Maine
What is the best way to increase CR?
I want to increase CR from 9.8 : 1 to 10.2 : 1 My 103 build should run stronger @ 10.2 : 1 with the 54s. How do I go about it? Mill the heads, cut the cylinders, change pistons? Which is the best way to go about it? Going to drop bike off to Indy tomorrow. I will listen to his advice but would like some input from some of the very knowledgable wrench heads on this forum. Check sig for what I have done so far.
Last edited by brickie; Mar 15, 2012 at 09:18 AM.
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I would mill the heads and while I was at it, I would have some mild port work and a valve job done. This will allow you to get to the desired compression ratio and your heads will flow better and give you more power. Check deck height and try to set the quench between .030 and .035. This will decrease the chance for pinging and you'll be glad you took the time to do the build right.
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I want to increase CR from 9.8 : 1 to 10.2 : 1 My 103 build should run stronger @ 10.2 : 1 with the 54s. How do I go about it? Mill the heads, cut the cylinders, change pistons? Which is the best way to go about it? Going to drop bike off to Indy tomorrow. I will listen to his advice but would like some input from some of the very knowledgable wrench heads on this forum. Check sig for what I have done so far.
Scott
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Cruiser
Joined: Jul 2006
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From: Andover, Maine
Thanks guys. I really appreciate your input. 1931 I have had some mild porting done by Bigboyz(no valve work as far as I know). Should have had CR matched to the cam while he had it apart (He also installed the 54's). Indy that is working on my bike now is going to call when he gets it apart and gives me his opinion on which way to go. There could be more questions coming. Scott in hindsight I wish I knew a little more about how this stuff has to work together 4 years ago. I would have drove from Maine to N.Y. and had you put in a 107 with your headwork and had something I would have been satisfied with the first time.
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From: san antonio
I want to increase CR from 9.8 : 1 to 10.2 : 1 My 103 build should run stronger @ 10.2 : 1 with the 54s. How do I go about it? Mill the heads, cut the cylinders, change pistons? Which is the best way to go about it? Going to drop bike off to Indy tomorrow. I will listen to his advice but would like some input from some of the very knowledgable wrench heads on this forum. Check sig for what I have done so far.
If you are at 9.8 now, that indicates that your chambers are about 86cc and you are running the OEM head gasket?? No drama getting to 10.2, mill somewhere between .015"-.020" and run a .030" MLS head gasket. However, with the 54 cams, 10.2 static is going to push corrected CR to 9.35, again no drama but cranking CR is going to be near 195psi. You might want include compression releases in the upgrade. JMHO.
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Thanks guys. I really appreciate your input. 1931 I have had some mild porting done by Bigboyz(no valve work as far as I know). Should have had CR matched to the cam while he had it apart (He also installed the 54's). Indy that is working on my bike now is going to call when he gets it apart and gives me his opinion on which way to go. There could be more questions coming. Scott in hindsight I wish I knew a little more about how this stuff has to work together 4 years ago. I would have drove from Maine to N.Y. and had you put in a 107 with your headwork and had something I would have been satisfied with the first time.
Scott
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Cruiser
Joined: Jul 2006
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From: Andover, Maine
Late to the party but just wanted to add a couple of thoughts.
If you are at 9.8 now, that indicates that your chambers are about 86cc and you are running the OEM head gasket?? No drama getting to 10.2, mill somewhere between .015"-.020" and run a .030" MLS head gasket. However, with the 54 cams, 10.2 static is going to push corrected CR to 9.35, again no drama but cranking CR is going to be near 195psi. You might want include compression releases in the upgrade. JMHO.
If you are at 9.8 now, that indicates that your chambers are about 86cc and you are running the OEM head gasket?? No drama getting to 10.2, mill somewhere between .015"-.020" and run a .030" MLS head gasket. However, with the 54 cams, 10.2 static is going to push corrected CR to 9.35, again no drama but cranking CR is going to be near 195psi. You might want include compression releases in the upgrade. JMHO.
I had Bigboyz put in compression relief buttons when he did my heads a couple years ago. Still running stock head gaskets also. Hopefully this (going to 10.2 CR) gets me the performance that this package should have. Also hoping that I can get it dialed in good with my T-max. We shall see.
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