This is a quick one. I've heard that when specing out a lobe the lobes actually grow in duration when placing them on the large ls1 core? For instance the ls1 core is a 55 mm piece. Now considering most lobes I assume in the comp master are measured with standard sbc or bbc core diameters does putting these lobes on a ls1 55mm core change the actual duration as listed in the master.

For instance if I spec a 256 at .050" ZS series intake lobe onto a ls1 55 mm core does it actually increase in duration when put on this ls1 55 mm core? Thanks.

Nick

 

I know that most of Comp's lobes are ground on Okuma CNC grinders which don't use solid masters. They use CNC coordinates. I suspect either the program can be tailored for cam base circle and/or the grinder software can compensate for grinding wheel diameter to give the same effective lifter motion (lift and duration at every degree) for a range of base circle sizes.

Non-CNC (mechanical) camshaft lobe grinders that use big steel master lobes are sensitive to base circle diameter and grinding wheel diameter. I suspect that if very accurate lobes are required with this type of equipment, grinding wheel diameter may be held very close for finish grinding. IOW, if the master was designed for a given base circle dia and a 23-24 inch diameter grinding wheel, the wheel would be used in that range, and when it got to the low limit, it could be moved to a roughing machine and used down to maybe 20 inches.

Cam lobe design not only looks at lift and duration, but also the derivatives of lift: 1)velocity, 2)acceleration, 3)jerk as well as snap, crackle, pop the proposed names for 1st, 2nd and 3rd derivatives of jerk. We can all feel lift, velocity and acceleration as well as jerk, the rate of change of acceleration like when you get the slicks to bite, or "come up on the cam", but Snap, Crackle and Pop go beyond my visualization and give me a headache when I try. The valvetrain has no such anxieties, so it responds to snap, crackle and pop. Therefore, absolutely precise geometry is critical. Enough already!

I'm in the precision grinding business, but not cams. Sometimes a well-maintained "mechanical" grinder can achieve better surface geometry than a ballscrew controlled CNC grinder. It might be difficult to measure the difference (which might be in small fractions of a micron) even with an Admore cam measuring machine, but perhaps Spintron testing could find the consequences of the minute geometry differences. I have heard differing opinions on this, especially from folks who grind high-end camshafts. In particular, I suspect very high rpm flat tappet cams might be the most critical. I think that someone, somewhere has run back-to-back tests. Unfortunately they don't share the information with me, so some of this is speculation...and some is not.

 

As per Crane Cams cam lobe catalog, the lobes "grow" roughly 2* @ .050" for each step in core size. Thus a Big Block Ford lobe would grow ~2*, a Small Block Ford lobe would grow ~4*, a Big Block Chevy lobe would grow ~6*, and a Small Block Chevy lobe would grow ~8* when applied to a 55mm LSx core.

 

Thanks for the replies guys, this is excellent information. After speaking with a comp tech which provided a link to the comp cams camaro which is similar in it's intensions to my 434 I'm rethinking my cam decisions all together. Thanks again.

 

There have been times where I used a 218 lobe and the cam doctor resulted in a 224 lobe after it was done. So always good to get a cam doctor sheet with each cam.

Rick

 

I may do that, I would imagine HPE has one. I'm sure comp has one so I could get it doctored through them as well. Thanks