How do you figure out how much valve overlap a cam has?




Travis

If I`m understanding your question correctly, that type information is usually found on the "cam card", a postcard-size piece of heavy paper found inside the box of a new camshaft. If you no longer have this card, you can look the cam up in the catalog or call the manufacturer, if you know the brand and part number of cam. Hope this helps you.

I have the cam card in front of me that I got from the crane website. It doesn't say anything about overlap..


here it is...

http://dab7.cranecams.com/SpecCard/D....asp?PN=109841

I think I have your answer.
Overlap is the period, in crank degrees, when the intake valve is just beginning to open and the exhaust valve is fully seated.
Looking at your cam card, cam timing section .004 lift, you'll see that the intake opens at 37* BTDC and the exhaust is fully closed at 39* ADTC.
To find the overlap we have to add the 37*, since it's BEFORE TDC (TDC being 0*), to the 39* which is AFTER TDC equaling 76* overlap.
Remember positive and negative numbers?? Think of it that way.

If I'm wrong I'm sure some one will correct me.

I think IGGY is correct. I have the Desktop Dyno software and it figures the overlap for you once you plug in the info from your cam card.

witch woould make 14 degres at .050 wich is wat most go buy and talk about. I think. Charlie

thanks bro's I just put the figures into my desktop dyno and it said overlap was 14*.. I didn't know it figured the overlap and it did


Just to make sure, overlap is when both valves are open at the same time right?

Does anyone know how much overlap is too much?

I have heard 4-6 with factory exhaust. but nos sure about others.

I have EMI's right now and planning on adding 1ft extensions onto the end of the riser's , hopefully this will help a little