keep compression at 10.5:1 or change it?
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Road Warrior
Joined: Jun 2009
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From: NYC
keep compression at 10.5:1 or change it?
Up coming upgrade to 103 on my 07 ultra. Planning on using stock heads which have been MCR and ready to install. 255 CAMs. Obtained some forges SE 10.5:1 pistons. Question is am I on the border of 92 pump gas and detonation issues....should I shoot for 10.25:1 to be safe ? Basically thinking changing gasket size + or - to put me below or under the bar. Thoughts? Mainly looking for low to mid range power...not really looking for the max power I can get at the max RPM the engine can handle.
Ultimate HDF Member
Joined: May 2008
Posts: 7,439
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From: 'Noke, VA
The 255 gives you a high CCP, but going with a thicker gasket is going to screw up your squish. With the MCRs you should be fine. Though at that CR I'd strongly consider a different cam.
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Road Warrior
Joined: Jun 2009
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From: NYC
Well, thanks for the info so far. What CAM's are better suited in the low to mid RPM range? Any chance that the volume added as a result of the MCR drilling will lower my compression ratio below 10.5:1. It's a pretty good size hole and even with the MCR's closed, the hole is pretty deep.
Road Master
Joined: Sep 2006
Posts: 1,062
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From: Arizona
Andrews 54 will run great. That is what you need.
Last edited by Indianspringsaz; Sep 30, 2011 at 04:57 PM.
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Road Master
Joined: Sep 2006
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From: Arizona
Change your plan if you can. Bore the cyl. to 107". Use CP flat top pistons and the 54 cams. CNC the heads now or when money allows. Tried and true combo. Be sure you keep the CCP down at 190 with that Ultra. You will not be happy with pump gas in the combo you are talking about.
Last edited by Indianspringsaz; Sep 30, 2011 at 04:56 PM.
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Thread Starter
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Road Warrior
Joined: Jun 2009
Posts: 1,943
Likes: 3
From: NYC
Change your plan if you can. Bore the cyl. to 107". Use CP flat top pistons and the 54 cams. CNC the heads now or when money allows. Tried and true combo. Be sure you keep the CCP down at 190 with that Ultra. You will not be happy with pump gas in the combo you are talking about.
Thanks. If the SE forged pistons will flat out not work....then I think I will just stick with the stock 103 flat tops that come with the stage II kit. I stumbled into the detonation issue at the 255 10.5:1 compression range and thought that if my MCR's added a few CC's ove volume and if I used a custom slightly thicker head gasket, I could stay right below the wire.