Piston dome
Seasoned HDF Member
Joined: Dec 2005
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From: poway
Stock 07 heads milled only to clean the gasket surface, 84.5cc CR works out to about 10.8 to 1.
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Tourer
Joined: Aug 2008
Posts: 403
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piston is a JE 107 10;25;1 part no. 317211 . called and tech says it is a +2cc dome. was told this compression is calculated with stock 85cc heads and .45 HG. any decrease in head volume or HG will increase this compression. does this sound right. thanks.
Last edited by harley#1; Feb 5, 2019 at 09:19 AM.
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,899
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From: poway
Calculator say 10.49 with those numbers is you set the HG id to 3.955.
http://www.bigboyzcycles.com/TwinCamComp.htm
http://www.bigboyzcycles.com/TwinCamComp.htm
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From: san antonio
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From: Viet Vet, crossroads
Concentrating molecular distortion from the breach at the far end of the azimuth ...of the flea fart,-
It can make as difficult as possible not to send the combustion and the aftermath the wrong direction, then it is a win win.
I have been watching everyone one here as to what they are doing. (outside the stereo and amp BS)
The only conclusive transaction of thoughts is this -without measuring it is all guessing.
The other thing is I have had trouble with online calculators in the past.
I was trying to use Big Boys about two years ago and it kept coming up two full points more then what I was coming up with.
There is a lot, and then a lot more to be said about the correct cam with static high CR ratio / dynamic,
as one does not have much to do with the other, as far as numbers for bragging rites.
It can make as difficult as possible not to send the combustion and the aftermath the wrong direction, then it is a win win.
I have been watching everyone one here as to what they are doing. (outside the stereo and amp BS)
The only conclusive transaction of thoughts is this -without measuring it is all guessing.
The other thing is I have had trouble with online calculators in the past.
I was trying to use Big Boys about two years ago and it kept coming up two full points more then what I was coming up with.
There is a lot, and then a lot more to be said about the correct cam with static high CR ratio / dynamic,
as one does not have much to do with the other, as far as numbers for bragging rites.
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Seasoned HDF Member
Joined: Dec 2005
Posts: 19,899
Likes: 8,006
From: poway
Concentrating molecular distortion from the breach at the far end of the azimuth ...of the flea fart,-
It can make as difficult as possible not to send the combustion and the aftermath the wrong direction, then it is a win win.
I have been watching everyone one here as to what they are doing. (outside the stereo and amp BS)
The only conclusive transaction of thoughts is this -without measuring it is all guessing.
The other thing is I have had trouble with online calculators in the past.
I was trying to use Big Boys about two years ago and it kept coming up two full points more then what I was coming up with.
There is a lot, and then a lot more to be said about the correct cam with static high CR ratio / dynamic,
as one does not have much to do with the other, as far as numbers for bragging rites.
It can make as difficult as possible not to send the combustion and the aftermath the wrong direction, then it is a win win.
I have been watching everyone one here as to what they are doing. (outside the stereo and amp BS)
The only conclusive transaction of thoughts is this -without measuring it is all guessing.
The other thing is I have had trouble with online calculators in the past.
I was trying to use Big Boys about two years ago and it kept coming up two full points more then what I was coming up with.
There is a lot, and then a lot more to be said about the correct cam with static high CR ratio / dynamic,
as one does not have much to do with the other, as far as numbers for bragging rites.
The output is only as good as the input. I've got a spread sheet that matches the BB calc pretty well. Probably due more to the precision which Pi has been calculated. CCP can be off as it's only an estimation..
Static versus dynamic.. There is a relation.. You are definitely not going to get 10 to 1 dynamic out of a 7 to 1 motor without pressurizing the intake tho. HDs typically don't get more much more than 100% VEs without fancy intakes (like single runner) and exhausts.
