I have always liked to try to figure out ways to compare knowns against unknowns, one of those things are comparing solid lifter cams to hydraulic profiles.
Solid lifter cams of course need to make up lash before a valve moves, some are rated at .015 tappet lift for adv duration, some are at .020, even Comp does some one way, some another. Hyd cams are usually measured at .006 tappet lift and do not need to make lash up, so today I compared two cams. The beauty here is I had both to measure and knew the performance of the 270H
The intake lobe on the solid cam from the cam card was 271 adv @ .020, 236 @ .050, 147 @ .200 and .333 lobe lift
The intake lobe on the hyd cam was measured, and from the cam card, 270 adv @ .006, 224 @ .050, 132 @ 200 and .300 lobe lift
To compare the 2 cams for DCR as well as general performance, I wanted to be able to compare the new cam's valve events to the 270H's on the same measurements. That meant measuring duration and calculating lift after the lash was made up at tyhe lobe and .006 was added, this should get closer to comparable duration measurements
So here is what I found, .016 lash / 1.76 rocker ratio = .009 lash at the tappet. To compare the rated value of the hydraulic, I added .006 of rise Comp uses for the 270H. So I measured duration at .015 to get comparable numbers at the tappet. On the Bullet lobe, that measured 280.5 degrees at .006 tappet rise after lash makeup
Doing the same for the .050 (measured at .059) I got 230 degrees on the solid, compared to the hydraulic .050 of 224
Again at .209, to compare duration at .200, I got 140 degrees vice 132 for the hydraulic.
Finally, lift figures, when comparing .333 tappet lift less lash, I got .570 at the valve, vs .520 (The differences in rocker ratio are included in this)
So, in the end, Bullet claimed this was a Comp 282S copy, which indeed it is, however when you account for the lash, you actually get something much milder than you'd expect
Specs for the Bullet - 271 adv @ .020, 236 @ .050, 147 @ 200 and .333 lift turns out to be much milder than you would expect
280.5 advertised at .006 tappet rise less lash, 230 @ .050, 140 @ .200 and .570 lift.
So here is the part to think about. I measured all of these planning a .016 lash at the valve, Bullet actually specs out this lobe at .028 lash, and Comp 282S's are at .022.
If I were to lash it where Bullet wanted that intake lobe, that would require .016 lash at the tappet, plus the .006 to compare it to the hyd. Which would have it under 270 degrees using this method, .050 adjusted for lash would likely be very close to 224 degrees, and .200 duration would be very close to the 270's value. In addition, that .333 lobe lift would be just barely over .550 at the valve
Something to think about, because although you'd have a bit more lift, and of course some benefit from solids at high RPM , essentially there isn't much difference in the hyd cam to the solid.
No surprise, because they say add 10 degrees for a similar solid to replace a hydraulic, but it's surprising when you do the measurement. Essentially a 270H is closer to a 282S than you'd expect when you compensate for lash