Roller Cam shafts

[rklaft]

Is there any reason i cant or shouldnt run a roller camshaft in my small block with solid lifters,, or would i be better off having a solid lifter cam ground to the roller specs that i want.
500hp,w2 headed 340, dirt track modified,,, thanks, Dave

[rumblefish360]

Yes there is. The key word s here are roller cam and solid lifter. A sure way to destroy your roller cam is to run a solid lifter on it when it should have one that rolls on it.

Get one custom ground or give the specs to a grinder.

[sanborn]

A roller cam lobe is designed for the roller lifter to run flat against the camshaft. Also, the camshaft lobe spacing is designed for the roller lifter to run in the center of the lobe.

A flat tappet lobe is designed different. First, the lifter must rotate on each lift cycle. The lifter is rotated mechanically, either by a taper on the lobe or more often, by the lobe being offset in the lifter bore. Either way will work. I'm not a camshaft expert, we need someone on here who is. I only know enough about camshafts to be dangerous!

Additionally, the lobe design is totally different for a roller and flat tappet. Using a flat tappet lifter on a roller camshaft will result in the lifter being "bound up" on the lobe ramp. The cam locks up! I know, I tried!

[perfmachst]

hello, solid cams are ground with .002 to .004 taper on lobes.the lifter bottoms are ground in a convex shape. this will allow the lifter to rotate at all times when motor is running.plus the lobes are offset from the lifter bores so they will rotate. roller cams have no taper at all. the rule is, flat tappet to flat tappet, roller to roller. another thing, a flat tappet cam will accelerate the lifter off the base circle faster than a roller cam will. after .200 lift, the roller has the advantage. just food for thought.

[DartGT66]

The materials are different too, that alone would kill the lifters (just like the oil shaft gear). Roller cams see much greater surface pressures tahn flat tappet cams, the contact area is much narrover, and therefore they have to be way harder material.

[rklaft]

Great job guys, great answers, thats what makes this forum #1
thankyou, Dave Haney

[michaelmopar]

i have a roller cam for sale. it is a 256/260 457/487. cam and lifters are less than 3500 miles of wear. its is a comp cam 110

[rklaft]

thanks for the offer but,, i need a solid lifter cam 620 lift 250 dur, will probally have it made by Racer Brown,, thanks Dave

[sanborn]

Dave- If you want .625" lift at the valve, you will need to order a camshaft with a significantly greater theoritical lift in order to net out a .625" lift. Why? The difference in the 59 degree lifter bore and the pushrod angle yields a lot of "lift loss". This is true for the exhaust and even more so for the intake due to the W2 pushrod "side angle".

I never realized how much "lift loss" occurred until I did some measuring with a dial indicator on the retainer about 12-14 years ago. We lost about .060" on the exhaust and about .090" on the intake. We too were wanting a "short" duration of about 252@.050" degrees and a lift of about .625"(net).

In order to get what I wanted, not only did it require another camshaft with more lobe lift, but 1.7 rockers as well to keep the duration "short". Racer Brown probably knows about this(Mopar Specialists). Back then all I had to work with was Comp and Lunati. They were good to work with but had no idea what I was talking about with "lift loss".

BTW, "stock" W2s like lifts in the .625" range(net). Properly modified W2 heads like lifts even higher---close to .700". These lifts are hard on the valve train especially on an oval track application. That is a good justification for the 48 degree block---it eliminates almost all the "lift loss" and is much easier on the valve train.

[rklaft]

Thanks sanborn, i think my choice for a cam will be racer brown so i will be
sure and discuss lift loss with him and make the needed adjustments. I guess our next quest will have to be a R block,, even though our season for
06 will probally only be 1000 race laps i need this to be durable and would like it to last the season. Thanks again sanborn, your a pleasure to chat
with. Dave

[rumblefish360]

They were good to work with but had no idea what I was talking about with "lift loss".

Now I was told that I was crazy and needed a timeout and schooling when I brought this up.
I was in Tn over the weekend. Just east of knoxville getting metal for the Cuda. I'm gonna have to get in touch with you in Aug. late for the next trip.

[pishta]

Lift loss....hmmm. Can we get some laymans geometry out and explain this? lifter moves up, rocker moves up, pushes valve down. Cam makers measure lift at the valve so isnt lifter loss factored in for a standard block? A Mopar 360 .625 lift cam at 1.5:1 rocker is what you are going to get, right? Ive included a diagram to visualize....

[DartGT66]

In the case of small block, the pushrod angle gets bigger with lift, therefore the lift at valve is reduced. In the case of BB with offset rockers, this isn't the case since the lifter is still pushing "upwards". In a SB, the lifter pushes upwards, and "away" from the rocker. The lift in the cam cards doesn't take this kind of things in to account, too many things affect the true end result. It's a directly calculated thing, 1.5 x cam lift.

[sanborn]

If you go through a cam maker's catalog, the cams are always listed by net lobe lift. They don't take into account valve lash, any losses in the valve train, etc.

And when they list lift based on a 1.5 or 1.6 rocker, they assume the true ratio is exactly 1.5 or 1.6. This is also not true.

The photo published is a good example, the difference in lifter and pushrod angle is about 15 degrees(have not measured, just guessed at it). Don't know what the loss is "off the top of my head"(have enough trouble getting hair to grow up there), but if that angle was 30 degrees, the loss would be 14%. The only reason I used 30 degrees as an example is I can remember that number "off the top of my head".

Now that we are talking about "losses", don't always believe what the manufacturer says about rocker ratios. Go back to the photo, look at the difference in the pushrod angle going to the rocker---and the angle of the valve. You have losses there too! And there are manufacturing tolerances to take into account. As an example, years ago(a long time ago) I built a jig to measure nodular iron rockers for a Mopar W2 head. The ratios varied from 1.36 to 1.48. Not a single rocker(out of three sets) measured 1.5. The purpose was to get a set as close as possible(through mix and match). Guess what---aftermarket rockers are better---but not perfect either. I have found this even on Jesel rockers.

[sanborn]

What we are talking about is Geometry---and I don't think they have repealed the "Laws of Geometry".

I'm getting old---being a bald headed geezer and all---but I am never too old to learn. Being a certified "old geezer", I don't suffer fools gladly---but love to teach---especially if someone wants to learn.

If an employee of a camshaft manufacturer told me I needed a "timeout and some schooling" about lift loss----well, I guess I would have to have a "prayer meeting" with that employee OR find another camshaft manufacturer.

[rumblefish360]

LOL, in my case, it's just local HP junkys.

[pishta]

Gotcha, so they base the valve lift on the lobe lift times the theoretical rocker ratio of 1.5? Hell, that would be a class action lawsuit in any other industry (remember the Ram HP claim at x000 revs when the factory limiter was 500 below that or the Hyundai HP claim that was inflated?)