Roller Rockers Anyone ????

[911TE]

The roller looks way too narrow to me. Roller rockers sold by speed shops have a similar sized roller over the other end meant to reduce side loading on the valve stem. Rollers on the cam typically are similar in width to a "plain" cam follower. Don't mean to sound critical, but these are highly loaded components.
Also, If you mean to use standard cams, the roller will need to have the same radius as the standard pad or the effective cam profile will be radically altered.
regards,
Phil

What Phil said is the most important part! The radius of the original rocker is pretty big, a roller with the same radius would be so big that there is probably not enough space under the valve cover to accomodate it.
Plus, the weight of this gigantic roller, which should indeed also have the same width as the original follower, would be as great or more as the complete old rocker, so the total weight of this new rocker would be double of the original one.

The only way to do this, would be to use the smaller roller together with a specially engineered cam profile, but then it is beginning to get expensive, not simply swapping rockers!

Sebastian

[Jeff Higgins]

Originally Posted by cgarr

Well said Jeff, Thats what I thought, isn't the roller usually on the valve? I would think with all the oil in there you would get some skidding of the roller on the cam lobe.

Yup, the roller is typically on the valve end. There is a significant "wiping" action of the rocker arm tip across the top of the valve that will actually kind of make the valve "wiggle" in the guide. It tries to push it away from, and pull it back towards, the pivot point of the rocker. The roller tip helps mitigate that.

In a pushrod motor, the pushrod side obviously doesn't have that problem. The top of the pushrod is free to move in and out on that axis as the rocker arm pivots.

[avendlerdp]

What our friend is proposing it really a roller "lifter" more then a roller rocker. See this Chevy V8 part:

http://www.shop.speedunlimited.com/Shop/Control/Product/fp/SFV/32401/vpid/4081409/vpcsid/0/rid/126429

Truth is there should be rollers at both ends as there would be on a hot rod V8. One on the cam and one on the valve. Probably not going to fit under stock valve covers but that's OK. Cavernous, billet valve covers are cool on Camaros. Perhaps the Porsche versions could have "The Heartbeat of der Fatherland" CNC machined onto the top.

Seriously though! The idea is a great one since it's getting harder to find oil that works in our engines and reducing friction and heat on the heads will never hurt either.

[gtc]

I was thinking about this a few weeks ago when I ran across an engine using LN's ceramic lifters.
What if we were to use a traditional rocker with a ceramic pad under the cam follower? You would have the simplicity of a traditional rocker (no needle bearings and no change to the cam profile) while reducing friction. You could probably stop worrying about ZDDP content as well.

Schubeck Racing, who made the ceramic lifters, has some pretty slick roller rockers, and it looks like they at one point made a rocker like the one I'm envisioning. Has anyone here had experience with these parts?

[2.7RACER]

Hi Mark,
Thanks for sharing your work in looking into roller rockers. I down loaded your avi file and really appreciate the effort you have put into this project. Well beyond my abilities with ACAD.
I have studied the Porsche rockers and found them to be more than a simple push here react there.
After studying the rocker carefully it became obvious this is a variable ratio design.
The wear pattern of the pad contacting the cam lobe indicates the rocker is at it's highest ratio
(approximately 1.5 to 1), when on the high side of the cam lobe.
Conversely at the base circle the ratio is less. Exactly what it is eludes me.
My measurements indicate something in the 1.4 to 1 range, maybe less.
I applaude your efforts to improve this design.
The engineering of ths part as it comes from Porsche is interesting to say the least.
I would certainly like to hear from John Dougherty regarding his view of possible improvements in this area.
Again, Thanks for sharing, great commentary from all.

[Natchamp]

Doug,

I appreciate your reply. A positive comment is always welcomed. I too have recognized exactly what you indicate. I haven't responded to most posts because everyone tends to jump in wagging their "___" playing ultimate engineer assuming I haven’t thought at all about this and simply drew the first thing that popped into my head. Anyways, my requirements call for a straight bolt in requiring no different cams. If my research ends in the conclusion that it can’t be done I’ll probably let it die.

I now have both the stock rocker in CAD as well as the new design. As time permits, I will have the cam, cam tower, and valves in CAD as well. At that point I will be able to actually see exactly what happens (to the valve) throughout the whole cycle comparing stock versus mine. My sense tells me acquiring an exact maximum lift will be no problem. The issue will be the duration because of the larger diameter shoe of the stock rocker and its varying ration, as you pointed out. I like the process and thinking so I’ll continue to pursue for now. Cheers.

[Racerbvd]

I have a set for my 914 2.1

[Bullet Bob]

I'm in the process of doing the same thing, though not for rockers. Here is a link.

http://www.youtube.com/watch?v=rHdngRrxCjM

Bob

[WI wide body]

Seems to me that roller rockers are a good idea. Long, long ago I had a 1964 Corvette Coupe that had a 327 with roller rockers. I didn't race the car but they seemed to work great, since I never had a problem.

Sure wish that I had kept that ride!

[A Quiet Boom]

Nat,

while a good idea, I don't think it will work with stock cams. I don't know the hardness of stock Porsche cams but I can tell you that V8 roller cams are hardened as opposed to non-hardened when running flat tappets. The shell of a bearing is hardened, if the cam is not of equal hardness the bearing will tear it up.

Also as stated by someone else the primary reason for going to roller valvetrain is to handle radical lift. When I was drag racing I was running a custom Lunati solid roller grind with over 0.750" lift on the intake side. A roller follower or tappet allows the engineer to increase the area under the curve by setting up very steep open and close ramps which effectively puts the valve near peak flow for a longer duration than is possible with a flat tappet or follower. When comparing a typical roller vs. solid lifter racing cam the roller has an almost oval shape to it while the solid lifter cam has more of a teardrop which means with flat tappets the valves spend more time at low lift, hence lessor airflow. In order to get full benefit a custom hardened cam with "fat" lobes would be necessary. I doubt there would be enough HP gain from frictional losses to justify a roller rocker even if it would work with the factory cam. The real gains for roller valvetrain from a frictional loss standpoint occurs with a pushrod engine where rollers are used on the cam lobe as well as the valve stem. Rollers at the valve stem also allow for greater lift without causing heavy side loading.

Having said that if you could run a wide bearing (take a look at a V8 roller lifter) with a custom cam hardened to the same hardness as the bearing and with a ramp profile designed to take advantage of the roller some real gains could likely be had although they may slow air velocity enough to put them into the realm of "race only". It is also true that a roller setup is going to be heavier but this is easily overcome with stiffer valve springs that would be necessary anyway to compensate for the greater valve acceleration as well as potential for greater lift. My race V8 ran triple valvesprings with ridiculous open pressures (800lbs comes to mind but it's been years). This was necessary to prevent valve bounce as well as big lift. To do it properly you would need to look at the system as a whole. Valve lift and timing should be setup to keep the valves near peak flow during each open/close cycle, vehicle weight, intended use, and other engine mods would all come into play. It's really a science.

I'd build one just for the heck of it and using a degree wheel measure lift every 5 degrees of cam rotation just for the heck of it compared to the stock follower, map it out on a graph in excel. Then if you had a scrap cam weld it up and regrind and see if you can't improve upon that. Someone on the board is bound to have flowbench numbers for a given head, see if you could build a profile that maximizes those numbers then see if a camgrinder couldn't grind a set of cams from blanks you produce on the CNC. It could be a really fun project.

[Joeaksa]

Subscribing. Wonder why Porsche has never done this... or have they and dropped it?

[911pcars]

Here are my specs for an aftermarket rocker arm:

Use precision cast steel for strength, reduced weight and long service life.

Explore state-of-the-art foundry techniques (e.g. counter-gravity casting) to reduce costs (pouring, machining, waste) while increasing material strength. However, this might be an OEM process due to initial setup expenses.

Use ti roller and axle on the valve tip end. Roller creates less side load on the valve stem/valve guide; reduces friction at the rocker shaft. Ti reduces weight

Keep friction foot on the cam lobe end and move the adjuster to the cam lobe end. This will be an engineering challenge, but the correct design will produce an adjustable as well as a replaceable friction foot. The adjuster screw, jam nut and roller can also be titanium to save weight. At a minimum, the jam nut can be aluminum or ti.

Make the rocker arm sillouette slim, including the ends. Narrow cross section results in less weight. Use spacers/shims to adjust side clearance and side-to-side alignment.

Use bronze bushing. Needle bearings provide less friction, but bronze bushings have a longer service life.

Provide a slightly higher rocker arm geometry for increased lift.

Provide an oil "well" to ensure adequate lube flow to bushing.

Position of the friction ends of the rocker relative to the center line of the rocker pivot shaft can result in a variable ratio lift, providing a faster opening valve w/o changing the shape of the cam lobe.

Explore relationship of factory mounting point of rocker shaft to valve tip and cam lobe. This area may provide optimization of the rocker geometry.

Roller rocker arms aren't reserved just for high lift cams. OEM's use them to reduce friction which results in better mileage and longer service life.

Sherwood

[Natchamp]

Boom, all good points. If the roller was the same rockwell as the cam or the stock rocker, wouldn't that negate the compatability issue?

Sherwood, sounds like a plan, let us know what the total start up cost is and the retail cost for a set is

[911pcars]

Mark,
Ha. What can I say except go for it.

Sherwood

[Kroggers]

Engineer or not, this sounds like a worth wile experiment. Keep going Mark and keep us posted...

[RWebb]

Can we list what we are trying to improve?

1. Is the failure rate high on rocker arms? Do we want it lower at the risk of sever head damage?
2. Are we trying to get higher rpm operation? (lighter wt. allows that)
3. Are we trying to get more hp from reducing frictional losses? IS the stock rocker a significant contributor to this (say, rel. to pumping losses, ring friction, etc.)?

I am just a little unclear on the benefits...

[avendlerdp]

Originally Posted by RWebb

Can we list what we are trying to improve?

1. Is the failure rate high on rocker arms? Do we want it lower at the risk of sever head damage?
2. Are we trying to get higher rpm operation? (lighter wt. allows that)
3. Are we trying to get more hp from reducing frictional losses? IS the stock rocker a significant contributor to this (say, rel. to pumping losses, ring friction, etc.)?

I am just a little unclear on the benefits...

If there is a roller on the valve side it will reduce valve guide wear. This becomes a benefit when using high lift cams.

I don't think the friction is a big power drain but a roller setup might hold adjustments better and allow the use of regular oil too. All good if the costs are not too high.

[A Quiet Boom]

Originally Posted by Natchamp

Boom, all good points. If the roller was the same rockwell as the cam or the stock rocker, wouldn't that negate the compatability issue?

Sherwood, sounds like a plan, let us know what the total start up cost is and the retail cost for a set is

I had that thought after I posted and the answer is I just don't know. I can tell you that in my industry I have seen setups where they try to use bearings as wheels on machines where a winder shaft is removable. Two bearings on the bottom per side that the shaft rests on then a third bearing clamshelled on top, the result is always a badly worn shaft. In one case however this did not happen and they where using a hardened shaft. Based on that and my intuition I'd say equal hardness would work fine. I'd also guess that thee factory cams are harder than a hydraulic type cam since they have to take the hammering abuse of valve lash. I suppose you could machine press on covers for the bearing shells that were equal in hardness to the factory cam. They would have to be precision ground however.

[sww914]

I would want set of these if they meet your goals of an exact replacement. Many wouldn't want to re-design the whole engine to work with the rockers, most would rather add a superior part that would improve performance and reliability and at a price that could be concealed from the wife. I would hesitate to make them overly strong, however. I've replaced broken rockers at the track as a result of a missed shift and the car was able to finish the weekend. That is a superior result compared to bent valves, broken valve guide bosses, dinged pistons and timing flange teeth cleaned off of the gear.

[911pcars]

Might I add that the our traditional rocker arm-cam lobe contact area produces high pressure and thus requires the zinc and phoshorous that's found in only a few brands of today's lube oil.

So, if an effective roller rocker assembly can be produced, this will reduce friction at this point, free up a fraction of engine power and reduce the need for special oil additives in the lube.

But this is not a small undertaking.

Sherwood