You asked for opinions, and the following is my opinion on the subject, so take it for what it’s worth.
I think your cam decision would be impacted significantly by both your riding style and the exhaust system you choose to use (stock exhaust or R pipes) so you need to figure these factors into your decision process. I believe you could run just about any cam you want (large or small), with no bad manners if you use the small stock 2 into 1 exhaust system and would have no issues at all with reversion (stuttering/blubbering in the mid-range before the pipe comes into phase). I believe Dave Hennessey could confirm this suggestion as his ’54 KH that he just got fired has KR E or F cams in it that would be comparable to or slightly larger than the J and K lobes you inquired about. I believe Dave is riding it relatively gently (not buzzing it up yet) and has not mentioned anything about bad manners. However with a large cam and straight pipes, reversion could be a real issue that could deleteriously affect how the engine runs in the mid-range. But, if you plan to keep it “on the boil” perpetually it may not be an issue for you.
In some circles the KHK cam has the reputation of being a very hot cam, when in fact it is not that large a cam at all, having ~ 242 deg duration @ 0.050” lift, and with this relatively modest duration provides an engine having excellent manners no matter what exhaust system you choose that will pull from the bottom to the top. The KHK intake and exhaust lobes are identical.
The -69R J & K lobes you inquired about are one of the final KR lobe sets made for flat track racing and were used in the dome piston engines, but should work fine in flat top piston engines as well. The J intake lobe is a significantly larger lobe than the KHK, having ~ 272 deg duration @ 0.050” lift - ~ 30 deg more duration than the KHK lobe! Regarding the K exhaust lobe, this is a much shorter duration lobe, having ~ 245 deg duration at 0.050” lift, and in my opinion is an equivalent of the KHK exhaust lobe, with the exception that it has a pinch more lift and duration than the KHK exhaust lobe, and I suspect there would be little, if any, difference in engine output using either of these exhaust lobes since they are so similar.
With respect to opening/closing timing, turns out that the J and K lobes have essentially the same exhaust opening/closing and intake closing as the KHK lobes. The only difference in opening/closing events is that the J intake opens way earlier than the KHK lobe and consequently increases the overlap area dramatically, which in turn may lead to mid-range reversion/drivability issues with straight pipes.
The image below is an overlay plot of the valve motion provided by the KHK and J&K lobes and shows clearly that all the added duration of the J intake lobe occurs on the opening side of the equation. Also note that the J & K intake and exhaust closings are gentler than those of the KHK lobes due to the longer closing ramps employed on the J & K lobes.
Hope the above provides some food for thought.
PS - you can also get the lobes you seek from Jim Leineweber
- KHK and JK cam comparison.jpg (94.75 KiB) Viewed 13468 times