HoLLo

iTrader: (17)

I have been searching for an answer to my question, and cannot find an answer as to how exactly cam lobes differ? I'm not trying to buy a cam right now, just something I've been wondering about when I read on cams... I understand cam geometry. I understand some certain lobes can ramp faster than others. But I just don't understand how. They way I understand, all cams have to have the same diameter before and after the lobe so the valve stays closed. And that being said, I don't understand what exactly makes the valve open/close faster and how you define this as a "lobe family"..

You have your lift and duration. I'm picturing a lower duration with a higher lift is going to give it a faster opening and closing, that's just geometry. But how do these "lobe families" make a faster ramp speed when the cam specs can vary so much?

Maybe what I'm looking for is simply as, what technically classifies a certain lobe as being in a certain family like XE-R, XFI etc.

01ssreda4

iTrader: (96)

That's one very incorrect statement. Most if not all aftermarket cams are cut on a smaller base circle then the stocker. I have a Cam Motion that has very aggressive/fast ramp lobes that is cut way smaller then my previous TR224. And, my pushrod length I'm running shows this smaller base circle is present

HoLLo

iTrader: (17)

Ok I was thinking of stock pushrod length in that statement, forgot to put that in.

01ssreda4

iTrader: (96)

I found that directly comparing my stock cam to a TR224, yielded a .050 difference in base circle diameter. Now divide that in half bc the lifter only rides on one side at a time shows you need a .025 longer pushrod to keep the same lifter preload. Now the grey area is most think stock pushrods are 7.400 inches. That would make it a no brainer to select a 7.425 pushrod right? Well some argue that for pushrod length you do not measure tip to tip but rather on spots on the ball ends just up from the actual tip. They claim that the stock pushrod is technically a 7.389 or something. I have calipered a stock pushrod to 7.40x, but again it comes down to where exactly you are measuring it from. Even with an .011 claimed shorter then the stock advertised, what about the rest of the .025? I hear people recommending 7.400 all the time. Most of the time I will recommend a 7.425 pushrod for someone running a stock application cam only set-up. With my Cam Motion, I'm running a 7.450 WITH the LS7 lifters which have a taller cup height vs. an original LS1 lifter. So yeah, it has a real small base circle.

HoLLo

iTrader: (17)

Good info there.

HoLLo

iTrader: (17)

Anyone?