Question on compression for gurus
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Intermediate
Joined: Jul 2008
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From: Iowa
Question on compression for gurus
I have a 105.33 with street port, 1.9 intake, heads cc'd to 85,.004 below deck, .040 gasket, with andrews 54 and books say ccp should be 187 to 190 depending on who's formula you use. I have 180 and both cylinders are within a pound. I don't have a second cp quage to compare to but my quage set is a snap on (30 years old though). Can the port and bigger intake valves effect the ccp.
Elite HDF Member
Joined: Jun 2008
Posts: 4,109
Likes: 9
From: Connecticut
No the valve size wouldn't matter as long as they were cc'd with those valves and I'm sure they were. Ports have no effect either. Just make sure the throttle is wide open while cranking the motor. Also how new is it? it may need the rings to seat to get up there, or the guage could be reading a little low, with an old guage it's very possable.
Ultimate HDF Member
Joined: Feb 2007
Posts: 7,663
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From: Northeast Ohio
Your quench is set at .044, ideal is .030. If you had it set there you would be right in the middle of your calculation. You also have to figure in the area from the top ring to the top of the piston as ring lands are set differently from manufacturer to manufacturer. I wouldn't worry about it if both cylinders are right there and only 1 lb difference.
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Intermediate
Joined: Jul 2008
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From: Iowa
It was bored a year ago but when the guy who did the machine work put the bigger valves in he didn't cc the heads and was low on hp and torque on the dyno so I took it apart this winter and he milled the heads. I told him then I wanted to go with a .030 head gasket but he likes to use a .040 and a .040 puts it at 10-1. But it also says ccp should be 187-190 thus my inquire. So the cylinders are seasoned and I just honed them and put it back together. Motor only had about 4,000 on bore job. Held throttle plate open with screw driver while cranking.
Outstanding HDF Member
Joined: May 2008
Posts: 2,543
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From: Ashland Ohio
You don't say what the static is for the piston itself. At any rate, I would go with Dalton and Scotty on this. Ride it and forget about it.Use this calculator and see what you have if it is bothering you too much.
http://www.bigboyzcycles.com/TwinCamComp.htm
HDF Community Team
Joined: Jun 2006
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From: san antonio
Trending Topics
Outstanding HDF Member
Joined: May 2008
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From: la
I went from 190 stock to 180 after 37's, I did pull my heads for the .030HG then later did the +4* crank sprocket and now I'm at 9.2 corrected & 190psi, just where I want to be.
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