Cam compression question
Seasoned HDF Member
Joined: Nov 2016
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From: Northern New Jersey
The advantage is avoiding situations where cam timing is such that at low rpm's ( cranking especially)compression is very low. Not how much a valve opens but the timing of it. At low rpm's cylinder pressure can be so low the thing wont start / idle all that well. Having a minimal static ratio helps avoid that.
Seasoned HDF Member
Joined: Aug 2008
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big IF
a lot of variables
idle quality like mentioned is one, no two engine will be alike even with same components.
my 01 sport runs around 10.5:1 static but probably 8>8.5:1 dynamic. my idle speed is 200 above stock just to idle. but the plus, i can run lower octane fuel with right ambient conditions. i also run retarded cam timing to shift the peak around 500 rpm upscale, built for speed, not low end grunt even though it is great due to transmission reduction to take advantage of international gearing, speedo is toast dropping out of 3rd.
now if the static was lower, then the hp/torque would be lower.
a lot of variables
idle quality like mentioned is one, no two engine will be alike even with same components.
my 01 sport runs around 10.5:1 static but probably 8>8.5:1 dynamic. my idle speed is 200 above stock just to idle. but the plus, i can run lower octane fuel with right ambient conditions. i also run retarded cam timing to shift the peak around 500 rpm upscale, built for speed, not low end grunt even though it is great due to transmission reduction to take advantage of international gearing, speedo is toast dropping out of 3rd.
now if the static was lower, then the hp/torque would be lower.
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,830
Likes: 7,968
From: poway
The manufactures list the static compression ratio.. Corrected is pretty much always the same for all cams as it uses intake close to set the CCP.. You can go 9.0 to 9.3 corrected for conservative build on a heavy bike. I've pushed it up to 9.8 but tune has to be spot on..
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Jun 6, 2019 04:23 PM
