There is nothing like a new build/rebuild to teach you things you almost didnt want to know.
In the process of working out this plan, I recently spent a day with my cam people. We jointly realized that there is a problem with this engine design, wherein the rear cylinder cam lobes begin lifting at the outer end of the pivoted follower, but the front cylinder cam lobes begin lifting closer to the pivot point.
They set me up with a good kit to map each of my cam lobes so we can get new cam designs worked up (including new unblown grinds, as well as a blower grind). Tonight I mapped every lobe of the most recent cams I had made for 2013, at .010" intervals.
What a deal. The front cylinder begins effective lift (the .050" point) 30 degrees ahead of the rear cylinder, but with .015" less lift. Additionally, the front cylinder lift graph, at the valve spring retainer, has two "bumps" in the lift lines, on both opening and closing ramps.
The rear cylinder has only one bump in the graph lines, during opening and closing. Curiously, the original factory cam design has highly assymetric lobes, with reversed (slightly non-matching) lobe shapes for the different cylinders.
Bottom line: My latest cams, intended to be 270 degrees effective, are only 231 degree duration on one cylinder, and 246 degrees on the other cylinder. With .005"-.0015" actual increase in lift, over stock, these cams are probably still not as effective as the stock cams.
This should be a lesson to anyone working with a single cam engine that has rockers or pivoted followers pointed in opposite directions. I wish I would have realized this 5 years and a few thousand dollars ago.
I would really love to see the cam graph for this engine (
http://8w.forix.com/penske-mercedes-pc23-pre-94-plans.html) because it used almost identical follower arrangements. If you scroll to the bottom of the page, there is a cutaway color drawing, where the short cam followers can be seen with the same geometry Honda used on these pushrod twins about 15 years before that Ilmor engine.
JimL