kul52

Thanks to this forum I have learned alot about what the cam spec numbers mean. I've got a pretty good understanding of duration, lift and LSA. I'm a little fuzzy on the different lobes but am enjoying reading and learning more about it.

I have two questions:

1) can someone explain how to calculate overlap by looking at the specs?

and

2) when a cam is listed as for example a LSA of 112 +4 - what does the +4 stand for and how does that effect performance, idle, driveability, etc

Thanks for any responses.

Matt-B

To calculate overlap: ((intake duration + exhaust duration) / 2) - (LSA *2)

Example for a 224/224 cam with 114 LSA:

((224 + 224) / 2) - (114*2) = -4 deg overlap @ 0.050" lift

Example for stock LS1 cam with 116 LSA:

((196 + 207) / 2) - (116*2) = -30.5 deg overlap @ 0.050" lift

Second question: +4 means 4 degrees advanced. Advancing the cam improves low and mid RPM torque but sacrifices high RPM horsepower. Retarding the cam sacrifices low and mid RPM torque but increases high RPM horsepower.

kul52

Thanks Matt - That helps a lot. I tried searching but couldn't find an explanation but figured there has to be a simple formula since I read posts where people were quoting overlap from reading cam specs.

I appreciate the input on the degreees of advance. That explains why the shop cam guru recommended a cam with +4 spec - my truck is a 4850 pound PIG and needs all the extra low ened and mid range I can find.

Thanks again