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Engine Mechanical TopicsDiscussion for motor builds, cams, head work, stripped bolts and other engine related issues. The good and the bad. If it goes round and around or up and down, post it here.
This winter I'm doing a 113" kit for a friend of the family who just bought a 2015 CVO Road Glide. Before I start calling around and we get the entire recipe figured out I briefly started looking around and seeing what options are out there. I came across a set of CP pistons with an advertised CR of 10.75
But when I use the Big Boyz calculator I'm only getting a CR of 10.06-1 with a .030" head gasket. Am I missing something here?
Now I'm curious. I wonder what they're using for cylinder head volume to calculate that ratio? Even though it says 10.75-1 when using SE Heads, It can't be 95cc.
There are several configurations of SE heads, all of which have 85cc chambers and none of which are CVO heads. Manufacturers have to use OEM specs to advertise product specs, like compression ratio. Using the BB calculator for a 4.060x4.375 configuration, .045" stock head gasket, 85cc chambers, assume 0.00 deck height and the 1.1cc dome height, static CR calclates to 10.77; pretty close to the advertised 10.75. Just have to be careful when using manufacturers data for planning purposes.
There are several configurations of SE heads, all of which have 85cc chambers and one of which are CVO heads. Manufacturers have to use OEM specs to advertise product specs, like compression ratio. Using the BB calculator for a 4.0060x4.375 configuration, .045" stock head gasket, 85cc chambers, assume 0.00 deck height and the 1.1cc dome height, static CR calclates to 10.77; pretty close to the advertised 10.75. Just have to be careful when using manufacturers data for planning purposes.
Ive seen multiple sources that claim 95cc. Im not trying to start an argument, I just want to iron this out.
I think what youre saying is even though the 110 heads measure at ~95cc they are advertised at 85cc?
I am not sure why you think we might be arguing? No argument on 95cc for CVO or 110 heads. You asked what you were missing with the advertised compression ratio when your calcs came up with 10.06 as compared with the advertised 10.75. What was missing in your calcs was the OEM head gasket thickness and 85cc chamber volume which is what the manufacturer uses to develop advertised specs. Maybe I misunderstood your OP but did not intend to start an argument.
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Question about advertised compression ratios
