How many rpm's can cutaway roller lifters typically add?

[groberts101]

Hi guys. I have my SBC apart right now for a single replacement ring and piston(overheated it last year because I didn't properly test/heat cycle to confirm new t-stat function before we quickly rushed off to make my son's football game ) and I found a small issue.

During pull-down I noticed there's a small and highly polished wear trench about .003" - .004" deep(smooth indentations without any sharp edges at near exact same width as the lifter wheels) beginning to form where these heavy assed Comp Cams hydro Magnums roll off the cams base circle and shortly upwards onto the flank. The correct terminology eludes me right now, but let's just say on the opening flank right where the round base circle stops and about 3/8"- 1/2" up onto the flatter portion of the flank leading towards the lobes nose. No scarring or scoring, lifters wheels are still round, polished, and very smooth rolling. I'll have to put it back together this way due to cost and time considerations right now, but would really like to know what causes this sort of thing to occur on a roller setup. I've seen similar many times in the past but it was always on heavily sprung and/or higher mileage setups far beyond mine. On the other side, I've also seen it on a few "heavily over-revved" LS stuff owned by younger kids who think they're going faster the higher they rev it.

Is the lobe lofting the rollers right off, or even partially across the cams base circle during short periods of over-rev?(this thing's fairly snotty for what it is, and I do miss a few shifts on occasion too). Maybe bouncing around after too fast a closing rate and ends up digging into the opening flank as it finally seats against the spring and gets forced to very abruptly start the whole process all over again on the next cycle?

As a quick side note, my valves aren't floating to any degree that can be heard or felt, but I am nearing coil bind(about .060" more to full stack height from my peak valve lift) with these little LS1 style beehives and maybe they are fully stacked at some point to cause some nasty skipping around?

Another and probably more likely cause here is just running too damned soft a spring for the valve-train weights, "super-awesome" lightweight bottom ended throttle response(bob-weight's deep into the 1500's), and 7,200 rpm 2nd gear shifts involved here. Seat pressure is only around 135.. with open pressure just over 370 @ .600 lift. FWIW, I just checked them yesterday to be sure springs were't going away on me and causing this issue but they're all actually still ABOVE advertised spec's. Valve tip wear patterns are dead on, valves are rotating well, and stem/guide clearance is still excellent.

Maybe it's just a case where the cam is getting a bit soft for the amount of lifter rise caused from my( although relatively small 230*/236* @.050") Extreme Energy hydro sticks more aggressive lobe being combined with a 1.7 rocker ratio? Last Extreme Energy solid roller grind used with considerably stiffer springs was without issue though, so it seems highly doubtful this little cam would be pushing that hard.

I'm guessing that I'm probably just beating the snot out of a mid-range torque cam that is under-sprung for my combo of parts and rpm range but I probably just need to hear it from those with more experience on the matter. Here are my valve-train spec's to hopefully better arm you guys with enough info to make this quick and painless. I've surely been a dope more than a few times in the past when it comes to pushing beyond parts typical boundaries .. so feel free to tell me if that's the case here again.

385 Chevy
Comp Cams XR282HR retro-fit hydro roller
Comp Cams Magnum retro-fit hydro rollers(.300 taller, IIRC and HEAVY)
Comp Cams 5100 wet belt drive
Ferrea 2.02"/1.60" valves
Comp Cams 26918 Beehives with tiny little Ti retainers
Comp Cams Hi-Tech Stainless 1.7 rockers(also HEAVY)
Smith Bros 5/16" x 7.300" x .080" wall pushrods

And before you guys start getting on me for wasting any time on this side of the rocker, my time is free right now and I do realize that there are heavily diminished returns in weight reduction involved here. But even if 15 grams of weight reduction on this side of the rocker only equates to around 4-5 grams of similar weight loss on the valve side of the rocker?.. I'm ok with that slight weight reduction for the hours worth of labor involved to find it. Band-saw will make quicker work of it and I know I can keep final weight very similar on all 16 if I keep my measurements and final cuts at least close to one another. I've lightened both sides of a roller rocker before and balanced them all to within a few tenths on both sides of the trunnion, so this should be cake-work in comparison to all that hubbub. Won't even attempt that mod on these heavy stainless roller rockers even though I know there's plenty of weight losses to be had there too without pushing too far towards failure. The required balance fixture is a PITA to get right and repeatable.

So, here's my question finally. How much rpm potential can be gained by cutting away(notching) the topside of these taller/full bodied roller lifters? 100.. maybe 200 rpm?

Anyone see marked differences when just moving from a full body to lighter cut-away style lifter without any other mod's being involved to muddy up an honest A-B comparison?

PS. I also have a set of Ti valve locks I was saving for another project but I'll be using those here now too since it will be better when cumulatively added to this lifter body mod. The Ti locks are worth 4 grams weight savings alone and I'll take every little bit I can find if it doesn't cost me too much time or cash to get it.

Thanks for any and all input.

[panic]

Can't address your question directly, but as to the value of weight removed from the short (pushrod) side vs. long (valve) side: it varies inverse to the square root of the rocker arm ratio.
1.7^.5 = 1.304, so tappet weight is worth 76.7% as much as valve weight. Your 15 gram example makes the tappet reduction worth about 11.5 grams.

Just a general comment? I've never seen a cam with that much damage re-used. Even if this pattern does not progress, the lobe rotation vs. lifter motion relationship is gone - you have 2 hooks in the curve.

[pamotorman]

I would use a rev kit to keep the roller on the cam lobe all the time.

[wyrmrider]

x2 on the revkit
rebuild your lifters if necessary
If it were mine I'd send the cam to Mike jones for a touch up and he can diagnose the problem
one of his grinds may give you more revs and or area under the curve and be more cost effective than cut away lifters
Do you understand why to use an inverse radius roller cam?
cheers

[les327]

x2 on the revkit
rebuild your lifters if necessary
If it were mine I'd send the cam to Mike jones for a touch up and he can diagnose the problem
one of his grinds may give you more revs and or area under the curve and be more cost effective than cut away lifters
Do you understand why to use an inverse radius roller cam?
cheers

No no sir i do not!

[MadBill]

You say the wear is on the opening side of the lobes. Is this correct? Valve float pounds the closing flanks in about the described location...

[wyrmrider]

OK I'll take a shot on the inverse radius
Engle and Jones are two fine sources
When trying to make a roller master one finds that the profile will not fit on the flank- almost flat - that can be ground by the large grinding wheels.
By using a smaller wheel- earlier 6-8 inches and now down to 2" the flank of the cam can be made concave which allows a shorter duration to be used instead of the longer duration required to get the same mid to high lift action.
This shorter duration gives some extra flexibility.
One can design for more action at any given seat duration
or
One can design for more stability or rpm
or
some combination.
Or one can design much more action at the same longer seat duration as the flat flanked cam.
Early on there were problems with low rev-ability which- correct me if I'm wrong here-were corrected using a computer program first developed my Mike's dad- The legendary Dick Jones- and improved over the years by Rick and Mike Jones (afik Rick is no longer in the cam business but he was really sharp)
Now Mikes profiles have prover high rpm ability as shown by the Indy car and other programs.
As Mike has said in several posts
He has profiles that look to have similar specs but have quite different spring requirements
you can guess the more spring is a fatter profile
This illustrates the problem of ordering a cam out of a catalog or specing cams from a grind list.
Without lots of experience- Like Joe does- you can't tell if the profile is for a heavy valve or light valve motor or what the rpm range is
and we all know how helpful the tech line is
So let's say that a motor requires a certain duration at 100-200 300
as shown by demand and head flows and experience
Inverse radius allows a shorter seat duration- an earlier Intake close- for more low end
and/ or more latitude in the overlap- you could start the intake open later and still get the flow when you need it
It allows you to get the exhaust closed earlier for less reversion and/or opened later

[Kevin Johnson]

...
During pull-down I noticed there's a small and highly polished wear trench about .003" - .004" deep(smooth indentations without any sharp edges at near exact same width as the lifter wheels) beginning to form where these heavy assed Comp Cams hydro Magnums roll off the cams base circle and shortly upwards onto the flank. The correct terminology eludes me right now, but let's just say on the opening flank right where the round base circle stops and about 3/8"- 1/2" up onto the flatter portion of the flank leading towards the lobes nose. No scarring or scoring, lifters wheels are still round, polished, and very smooth rolling. I'll have to put it back together this way due to cost and time considerations right now, but would really like to know what causes this sort of thing to occur on a roller setup. I've seen similar many times in the past but it was always on heavily sprung and/or higher mileage setups far beyond mine. ...

An acceptable hardening process for certain internal combustion engines is roll hardening or cold working a crankshaft by rolling fillets on the edges of crankpin and main journal segments.

[groberts101]

You say the wear is on the opening side of the lobes. Is this correct? Valve float pounds the closing flanks in about the described location...

yeah.. base circle on upwards into the opening ramp by about 1/2" inch or so.. maybe even slightly more figuring the tapered edges of the pattern on either end. Which is what has me confused as to what the possible cause could be for wear in that particular area. I really should have taken some pic's before I started buttoning everything back up but I haddn't figure on posting the question after talking to my machinist and a few other local racers I used to run with on the streets. They said.. "run it and quit over-revving such a little cam".

Bothered me enough to spend the time on the forum this morn to ask others with much more roller cam experience under their belts.

[Kevin Johnson]

Make sure that it is wear rather than displaced metal. Check the lifter to bore clearance that might allow one or the other side of the roller to apply concentrated pressure. It goes without saying that the axis of the lifter must be normal to the lobe surface so that the roller surface is parallel to the lobe surface. Lots of ways for this to go astray, obviously.

SUMMARY OF THE INVENTION The selective cold rolling method of the invention involves the use of cold rolling equipment such as is commonly used in connection with propellor shafts on ships, however, instead of using a constant roller load and introducing residual compressive stresses uniformly around the circumference of a shaft, the roller load is varied selectively so as to use a higher roller load, with consequent higher residual compressive stresses, on the inside of a bend thereby tending to straighten the shaft. The selective cold rolling of a shaft is accomplished by pressing a small roller against the shaft with alternating loads as the shaft is slowly rotated. A specified length of the shaft is rolled by slowly advancing the roller along the shaft as it rotates.

The roller has a crowned face and is sized with radii of curvature which are much smaller than those of the shaft such that a very small elliptical contact area exists between the roller and the shaft. The combination of a heavy roller load on the shaft and the small contact area results in very large contact stresses between the shaft and roller. These stresses cause a yielding of the shaft material near the surface which then leaves a residual compressive stress in the material adjacent to the surface. By controlling the roller load, the magnitude and depth of the residual stress can also be controlled. The residual stress over the yielded depth actually produces a residual force in the area adjacent to the shaft surface and it is this residual force which is utilized to straighten a shaft.

[MadBill]

Yes, opening flank wear is more likely a material hardness issue. Solid roller cams run ~ RC 58-60; don't know about hydraulics...

[groberts101]

OK I'll take a shot on the inverse radius

thanks for the very detailed reply and "inverse radius 101" crash course in the above. I'm fairly familiar with the technology but will only spend that kind of coin on the future little SBF motor I pretty much plan on being buried with. Don't really even want to have this cam reground unless absolutely necessary to avoid selling someone a ticking time-bomb. Don't need that kind of bad Karma floating around to come back at me later on.

This motor just gets repaired and lightly freshened to get ready for sale this summer so I'm simply looking for a few extra rpm to ease the potential for longer term wear. It runs well past the expected rpm potential of this little cam and I know that the next owner will very likely also take it up to 7,000 as well.. simply becuase it ET's better when you do run it harder.

So far I'm planning on mod'ing the lifter bodies with a cutaway right up to the link bar(maybe 15 grams or so lost there).. cutting the excess material off the rocker cup ends(due to the 1.7 ratio relocating the cup towards the trunnion, there is an extra .100 thou or so on the outboard end of the cup I can whittle off(maybe another 3 grams).. and finally use the Ti keepers to cut another 4 grams or so off the valve side. Hope that gives me some more leeway to keep the rev limiter where it's at right now. Otherwise, I may just cut another 100 - 200 rpm off the rev limiter even after all is said and done to allow more margin and longevity.

[Kevin Johnson]

That might reduce the leverage afforded by the bore to lifter and help transfer wear to the bore/lifter interface rather than the cam lobe. This is assuming some misalignment of course.

[groberts101]

Make sure that it is wear rather than displaced metal. Check the lifter to bore clearance that might allow one or the other side of the roller to apply concentrated pressure. It goes without saying that the axis of the lifter must be normal to the lobe surface so that the roller surface is parallel to the lobe surface. Lots of ways for this to go astray, obviously.

Thanks, Kevin. Lifters are pretty decent with some high polish, but no scuffing or linear scratches anywhere. Lifter bores were indexed and honed years ago and are still in perfect condition as well.

The other thing I did notice today, as I kept this scenario in the back of my mind, was that the link bars do have some slight play which may be allowing the lifters to slightly rotate as they load and unload while going on this merry-go-round?

That seems much more plausible an explaination than the lobe being too aggressive for the rocker ratio and the springs I have. If grabbing the pair of tied lifters with one in each hand.. each one can be twisted by about maybe .010 - .015" in either direction.

[Kevin Johnson]

Greater restriction of degrees of freedom of movement would have dire consequences for some random engine with misaligned bores. Maybe two lifters could be constructed with axially located drill rods of some extended length. That would make it far easier to check for skew.