Calculating Overlap

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Hmmm. When I input my cam specs it comes out to 32* of overlap. Doesnt seem right for a solid roller with .405 lobe lift.
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Unless I misread, instructions say overlap cant be figures at .050 .


You are correct. That’s not for calculating overlap with @.050 timing.

I used an online calculator to get the @.050 numbers I posted. So the 37* @.050 is correct.


Edit...damn dyslexia...@.050 overlap is 32* and that’s my final answer.
 
Option 2 says for advertised duration? Isnt that different than .050"?
It's good there is a known formula for calculating this. Now for my thick skull to retain at least some of this....
Wider LSA means LESS overlap which moves torque curve up....:realcrazy:
It’s there. It’s like the second option down the page.
 
I use a variation of what they’re doing.
I use advertised intake duration + exhaust duration, divided by 2, minus 2 times the lsa.
Let’s say you have a cam that’s 285/295-110.
285 + 295/2 = 290
290 - 220(110x2)= 70 overlap
 
285+295=580
580÷4=145
145-110=35
35×2=70
In this example it's the same, but I'm curious what would the differences mean? I'm still trying to learn.
I use a variation of what they’re doing.
I use advertised intake duration + exhaust duration, divided by 2, minus 2 times the lsa.
Let’s say you have a cam that’s 285/295-110.
285 + 295/2 = 290
290 - 220(110x2)= 70 overlap
 
There is no difference.

The result is the same.

It’s like saying there’s a difference between 3 + 2 vs 2 + 3.

With a single pattern cam you can skip the first step.

It’s just the advertised duration - (lsa x 2).
MP 292 cam....... 292-216= 76

Comp 280 Magnum........ 280-220= 60
 
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Because I am too lazy to think this hard in the morning ...what do you come up with for my cam specs ?
 
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Because I am too lazy to think this hard in the morning ...what do you come up with for my cam specs ?

It comes up with 32 using PRH's method. But that is short of actual overlap because it's using the .050 numbers.
 
It's hard to figure the overlap of a solid lifter cam , from the advertised numbers, in a way that is comparable to a hydro.
IDK if there is a way.

Even among hydros you can get tripped up by how various makers determine their advertised numbers. For example, there are two popular starting points; namely; .008 Tappet rise and .006 rise. and then there is .001. From these numbers it is possible to calculate the valve-opening points, but that's a real can of worms. For instance; your arms may in fact be 1.50 ratio, so you are maybe expecting 1.5 x .008= .012 valve open, but once installed, your 1.5 arms may only measure as 1.42 for; 1.42 x .008= .0114 Doesn't look like much difference, but could be 2 degrees at each end, and so your 268 becomes a 264, or maybe less.
For hydros I use the same method that @PRH uses

IIRC, Solids are advertised from .020valve open. But can be whatever the seller wants to measure from.
So how do you compare .020 valve open to .008 Tappet rise?
I know of no way.
 
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