How to figure cam overlap?
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Re: How to figure cam overlap?
Add up in,ake and ex duration and divide by 2.
Divide that result by 2 again and subtract lsa.
Multiply that x2. = overlap.
Divide that result by 2 again and subtract lsa.
Multiply that x2. = overlap.
Re: How to figure cam overlap?
# of degrees the intake opens before TDC + # of degrees the exhaust closes after TDC
Example:
Intake opens 30* before TDC
Exhaust closes 30* after TDC
Overlap = 60*
Keep in mind that it's going to depend on where on the lobe you're measuring the duration, too. The overlap measured at effective seat duration is going to look much larger than if measured at .050" lobe lift.
I hope this helps. - Brad
Example:
Intake opens 30* before TDC
Exhaust closes 30* after TDC
Overlap = 60*
Keep in mind that it's going to depend on where on the lobe you're measuring the duration, too. The overlap measured at effective seat duration is going to look much larger than if measured at .050" lobe lift.
I hope this helps. - Brad
Re: How to figure cam overlap?
F-BIRD88 :
I am having issues trying to make your formula work?
A cam has 232 @ 50 intake duration and a 242 @ 50 exhaust duration with a 112 LSA
Using your formula as given - 232 + 242 divide by 2= 237 divide by 2 = 118.5 - 112 = 6.5 x 2 = 13 degrees overlap ?? seems a bit small ??
I am having issues trying to make your formula work?
A cam has 232 @ 50 intake duration and a 242 @ 50 exhaust duration with a 112 LSA
Using your formula as given - 232 + 242 divide by 2= 237 divide by 2 = 118.5 - 112 = 6.5 x 2 = 13 degrees overlap ?? seems a bit small ??
The Older I Get, The Dumber I Get
Re: How to figure cam overlap?
Overlap is “usually” associated with the advertised duration.
In the above example, 13 is correct for overlap @.050.
I do it similarly to the formula you used if I don’t know(or want to calculate) the open and close points.
Duration for intake/exhaust added together, divide by two, minus two times the lsa angle.
232 + 242 = 474
474/2= 237
237 - (112 x 2) = 13
In the above example, 13 is correct for overlap @.050.
I do it similarly to the formula you used if I don’t know(or want to calculate) the open and close points.
Duration for intake/exhaust added together, divide by two, minus two times the lsa angle.
232 + 242 = 474
474/2= 237
237 - (112 x 2) = 13
Somewhat handy with a die grinder.
Re: How to figure cam overlap?
Got it, forgot to think advertised versus @50.
The Older I Get, The Dumber I Get
Re: How to figure cam overlap?
can be a noticeable difference mine was about 5 deg at .050 but at .006 its 57 deg overlap
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Re: How to figure cam overlap?
Some time back I composed an excel, it backwards calculates from overlap and LSA to int and exh duration.
https://www.speed-talk.com/forum/viewtopic.php?f=1&t=54556
https://www.speed-talk.com/forum/viewtopic.php?f=1&t=54556
Mike R