Valve lift calculation
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Burning Brakes
Joined: Jul 2013
Posts: 963
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From: Vancouver, BC
Valve lift calculation
Hi guys
How does one calculate valve lift? A cam that has .489/.504 gross valve lift and a cam that has .487/.490 valve lift.
If the intake rocker is 1.6, how much do these figures increase by? How is the calculation done?
How does one calculate valve lift? A cam that has .489/.504 gross valve lift and a cam that has .487/.490 valve lift.
If the intake rocker is 1.6, how much do these figures increase by? How is the calculation done?
Tech Contributor
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From: At my Bar drinking and wrenching in Lafayette Colorado
The cam manufacturers specify what rocker arm ratio the rated valve lift is at. The cam card, and the spec sheet, will state, "valve lift with 1.5 rocker" in the case of small block Gen 1 Chevys, or "valve lift with 1.7 rocker" in the case of a big block. If you change from a 1.5 rocker to a 1.6 rocker, you simply take the lift with 1.5 rocker, divide by 1.5, and then multiply by 1.6.
Last edited by lars; Mar 19, 2021 at 07:34 PM.
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Le Mans Master
Joined: Aug 2017
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To get the actual lift of the lobe only, take the valve lift and divide by the rocker arm ratio.
Using your 490 lift example:
490 divided by std rocker ratio of 1.5 = .327 inches. That is the lobe height above the cam circle.
Once you know your lobe height, usually provided by the cam company you can play around with different rocker ratios and get different results.
.Again, 327 lobe X 1.5 rockers = 490 valve lift.
However, .327 lobe X 1.6 rockers = you now have a 523 valve lift, and so on.
Using your 490 lift example:
490 divided by std rocker ratio of 1.5 = .327 inches. That is the lobe height above the cam circle.
Once you know your lobe height, usually provided by the cam company you can play around with different rocker ratios and get different results.
.Again, 327 lobe X 1.5 rockers = 490 valve lift.
However, .327 lobe X 1.6 rockers = you now have a 523 valve lift, and so on.
Le Mans Master
Joined: Aug 2017
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From: Cool Northern Michigan
Now that your fart has vaporized I will transfer you to our billing dept.
O.P. Titanie
Date: 3-19-21
Issue: Cam lobe lift calculations
Result: Solved
Number of posts: 6
That will be $119.
How do you wish to make your payment?
O.P. Titanie
Date: 3-19-21
Issue: Cam lobe lift calculations
Result: Solved
Number of posts: 6
That will be $119.
How do you wish to make your payment?
