Geoffrey

Colin was kind enough to send me one of his DLC coated CNC machined rocker arms for a look. For those who are not familiar with the rocker arm, it is:

1) Lighter than stock
2) Available in screw adjuster and lash cap versions
3) CNC machined from special metal alloy
4) Stronger than stock
5) Has a larger pad area so it won't fall off a high lift cam lobe
6) Modified oiling passages
7) Is DLC coated for friction reduction

I have been considering these units for my new engine so I sent one to my camshaft manufacturer along with a stock 901 rocker and a 993RSR rocker for comparison. This involves installing the rocker arm in a head and cam tower and running it on a spintron machine and comparing the valve motion profile with a known camshaft profile.

The results are interesting.

1) There was a variation of .004" of valve lift between the batch of stock rocker arms I sent him with the 993 RSR rocker arm providing the most lift.

2) There is significant variation of the rocker arm ratio through its travel and the variation differs between the batch I sent.

3) The 9M rocker was consistent across its motion and has most closely matches that of the 993RSR rocker arm with very little difference in the valve motion profile - .001".

Because of the longer pad area, the camshaft can use a higher peak valve velocity in the valve motion profile to allow for better use of the valve opening and closing ramps. My camshaft grinder's comments were "significantly improved". This combined with a more consistent tolernace means that the engine should run smoother and stronger.

My new camshaft will be based off of a billet steel blank and micropolished much like the ones that we are doing for the 9M USA conversions except that I will have him micropolish the race camshaft to a more fine finish. When combined with the DLC coating, this should reduce the friction of the valvetrain. There is no way I'd consider using the factory rockers again on a racing engine.

Perhaps Colin can post some nice pictures of them...

Premier Motorsp

Which version 993 RSR rocker? The original lash cap one or the later adjustable rockers?

How much variation in a batch of 12 regular rockers? What I mean is if you install a set of 12 regular rockers in an engine, how much (based on your results) would peak lift vary?

Geoffrey

The 993 RSR rocker arm that was tested is the adjustable version with the Torx elephant foot.

There was a .004" variance in the peak lift for the batch of rockers tested. Further, they varied with the rocker ratio as well.

NineMeister

Here are some photos of the two different 9m cam followers, the adjustable one we call the single pad and the lash cap version is the two pad. The single pad rocker is photographed with a 993RSR adjustable rocker alongside it, the two pad is next to the equivalvent factory two pad 935 rocker. The 3D CAD rendition is from the Catia model and showns some of the side milling detail that we do in order to reduce weight from areas of low stress.

Some of the details which are less obvious are the longer cam pad lengths of the 9m rockers in comparison to the factory parts, a requirement of the design specification to permit 15mm of valve lift (0.591"); behind the main pad we use quite large fillet radii to properly support the pad - poor pad support is a design fault on the 993RSR rocker which allows flex of the contact face resulting in uneven pad wear.

The 9m followers are made from a specially selected alloy steel, heat treated, super finished and finally DLC coated to reduce friction and hence wear. Although they are CNC machined, because of the strength of the material chosen they are slow to manufacture due to the cutter sizes required for the finished item, add in the material cost, finishing and DLC coating and it is easy (for an engineer) to understand why they cost £200 each, but if you want the best....

ThomasC2

Cool Colin! yours looks like the real thing and the Porsche item looks like a copy from China...

NineMeister

Thanks Thomas, funnily enough that's pretty much how they perform in the engine as well.

Geoffrey

Update:

We have just finished the geometry evaluation and camshaft specifications for a valvetrain built around the 9M billet rocker. We used the head flow data from the 9M head that we did 3 years ago when Colin first introduced the head, measured on our Superflow SF600 flowbench. Then we combined the geometry data from the 9M rocker arm to determine an optimum camshaft profile for my new engine design. I am using a longer connecting rod and want to alter the peak power range, so the camshaft profile requires alteration. The new profile is similar seat duration as before, however because of the 9M rocker, we can use more agressive opening and closing ramps, and therefore, have more duration when measured at .050" of lift. Since the rocker arm has a longer pad follwer, we can also lift the valve more. All of this promotes improved cylinder filling.

The interesting part about the validation here in the US, using independant engineers is that we have come up with almost the same specification as Colin and his engineers designed in the UK. The camshaft is very similar to the one Colin is running in his 4.0l engine with exception that I'm running a narrower lobe centerline due to the fact that my car is a pure race car. The other intersting thing is that the spring force requirements for seat pressure and nose pressure have come in within 10lbs of what Colin has designed. I'm happy because two different sets of engineers have come up with very similar answers.

I know there is a lot of discussion about whether or not the 9M parts work, whether they are as good as Porsche's, how long they will last, etc. After running his components in my engine, and because of all of the validation work I've done, I believe in the products, and feel that they are directly responsible for the power my engine produces. Now, granted, my engines have been designed as a system, and simply installing a camshaft, or head, or whatever, won't necessarily give you the ultimate performance. The parts have to be developed to work together. It's good to see 10 year newer technology available for the air cooled engines.

Steve Weiner-Rennsport Systems

Nice looking stuff,..my compliments to the "Chef". Something like this has been long overdue to address deficiencies in the valve train.

With some long-term validation to ensure durability, I think they will be popular for the folks looking for max performance from a track or race engine. At $3600/USD per set, one will need some assurance that they are as reliable as OEM or better.

Nicely done!

Geoffrey

Hi Steve,

Colin has been running a set of the DLC CNC Rocker arms in his 993RS for several years and I believe he has won 1, maybe 2 championships with them. In addition, I believe he has 2 customer cars outfitted with the rocker arms.

I am looking forward to testing these in a full racing environment. I am going to have the camshaft specially prepared for running the rocker arms. It will be micropolished to a RA of 1.0 micro inches rather than the 1.5-2.0 that I've been doing on the latest cams. And the cam will be a steel billet, not a chill cast core and will be nitrided. I would have done those items anyway since the reduction in surface roughness has seen a 2hp difference on a Spintron machine on a 400hp engine.