New monster racing cam with smooth ramps

JS
ramps of a cam lift curve are pretty meaningless, for they tell nothing about the velocity of the ramp as seen at the valve in a running engine. To reveal this in a computer analysis is a very complicated exercise, and geometry of the Commando valve train is necessary, which differs greatly to that of the Harley.
As Dances implies, a static design is one thing, but a dynamic evaluation and comparison is another matter entirely, and it would be of considerable interest if you would explain how this was done.

acotrel said:

I note your comment about heat build-up in Commando engines when using petrol, it might be very relevant to this topic. If you advance the cam, the exhaust system gets extremely hot. I think it is because the charge goes further down the pipe before it gets stuffed back into the combustion chamber.

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Acotrel
Muddled thinking I'm afraid.
This is basically an issue that involves time and distance. The length of the header pipe dictates the distance a pressure wave must traverse, and the time is determined by the speed of a pressure wave in a hot exhaust gas.
The main variable is the engine speed.

Kvinnherring - The smooth ramp cam is easier on the valve train. For the street I would recommend the JS2 rather than the JS3. The JS2 being similar in performance to the PW3 but with much higher RPM capability without valve bounce.

Dances - Yes the Harley has rollers and a 1:48 rocker arm geometry compared to the Norton geometry of 1:14 Both were measured at the lifter (not the cam) and the Harley profile was recalculated to produce a profile THAT GAVE THE SAME VALVE DURATION AND LIFT BUT WITH A 1:14 ROCKER ARM RATIO. Then the two could be compared. This was just the starting point which led to a more gradual ramp for the JS "smooth ramps" which have less velocity on the opening and closing ramps.

Snotzo - See the jerk graphs below. The JS3 jerk (black line) is reduced by approx 1/2 of what it is on the JS3/Sifton 460/D+ grind (.3 jerk compared to .6+ jerk). Ignore the red line - its an acceleration curve and is not shown on the JS3/Sifton 460 graph (both acceleration curves are there but one came out a mirror image dipping downward and was cropped out).

The computer analysis was performed by two different camshaft companies that had all the required software as well as CNC cam grinding equipt. I sent them the cams and lifters for accurate measurements and spent about 2 years on and off working out the details that finally led up to lift and duration specs to an accuracy of 7 digits. I couldn’t have done it without their help. But now I can have cams made by CNC machine or by the more popular cam grinding machines requiring master cam plates.

Hi Jim, what about running a JS3 cam in a spintron, same as we did for one the JS 2 cams that I bought off you?
Regards Mike

Yes that would be great. The 1st JS2 cam I sent to you was not a smooth ramp cam. It had the same profile as the PW3 with its harsh ramps. More gradual ramps to avoid valve bounce were necessary so I went to the trouble (with a lot of help) of re-designing the 1st JS2/PW3 with better ramps to eliminate the valve bounce. The improved JS2 smooth ramp is what you got with the 2nd JS2 cam you ordered from me. The spintron tests are what motivated me to create the JS2 and JS3 smooth ramp cams and I have you to thank for encouraging that to happen.

Well done, taking note of customer feed back.
Getting closer to running the 2nd JS 2 cam in the 880 motor.
Regards Mike

jseng1 said:

The spintron tests are what motivated me to create the JS2 and JS3 smooth ramp cams .............

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Did you do spintron tests? If you have any video of the spintron tests for the JS2 and JS3, that would be cool to see.

Comstock did spintron tests of the PW3 cam and the early JS2 cam. They both had the same valve lift and duration. The JS2 cam could rev much higher than the PW3 because of the lightweight BSA lifters and the beehive springs (the Beehive springs alone are good for another 500 RPM over RD dual racing springs according to a racer with his 9000RPM 500cc screamer). But I could see there was a problem with that profile so I changed the ramps and now the ramp jerk loading has been cut in half. The smooth ramp JS2 should now out rev any other Norton race cam with flat lifters - and by a wide margin.

Dances - I think you should be thinking about a Sifton 480 cam with smooth ramps. This would be the ultimate top end Norton race cam. But I'm not sure there would me much market for it.

Thanks Jim.