cam grinding -

Did you ever do a cranking compression test on the engine before and after cam phase changes?

Stan

Something like that thing on Winky's Workshop?

- now at the

CVT to an intermediate jack shaft really helps with that.

Generally you advance timing with an offset key (if it has a keyed balancer) giving you a degree or two. Much better than a sudden shift of 14.

Generally they go the other way with those engines at the cost of engine life. MORE rpm, with more gas, more air, and a more open exhaust, elimination of the governor, and stronger valve springs. That is basically stage 1. Sometimes before upgrading engine internals they will mill the head for more compression. I've seen YouTube hotrodders do it on a sanding belt.

Generally, instead of trying to build low end torque with a tiny engine they built horsepower, and increased the gear ratio and they launched at higher RPM.

Some of the older early videos from guys like Red Beard's Garage and Cars and Cameras from when they were still doing it mostly for fun really do some interesting cheap mods on those small engines. Sure a top fuel mini dragster built around an alcohol fuel turbo charged predator 670 is entertaining, but I more enjoyed their older shorter videos where they took an EX21 with basic mods and stretched another 5-7 mph out of it. If you must play with the 670 dropping one bonestock on an old Paughco Springer frame was more approachable and made it more interesting.

For reference I've got a couple Manco Intruder II carts I bought for the kids years ago. Even with the Subaru Robin EX21 (6.5hp) they run a CVT to an intermediate jack shaft and then a tiny gear on the jack shaft to a giant gear on the drive axle and run only 16 inch tires. They do run turf/sand knobbies, so take off torque is important, but I think they are locking up at a much higher rpm than you are thinking.

When I was a kid those who were lucky enough to have an old classic 5HP cart with a simple belt/lever friction clutch were running tiny tires.

I'm not sure an RV cam (long dureation) translates significantly to a

I'm just talking. I didn't really analyze your post thoroughly.

Can you grind some off the base circle and get the lost lift (and more) back? You will have to add length to the follower region (pushrod, bucket follower, whatever you have) to keep the geometry correct at the valve tip, I don't know that valve train so can't help there.

There's a engine good discussion website called speedtalk.com (unfortunately it's been fighting off bots for a week so response time is very slow at the moment). One of the long time posters goes by SchmidtMotorWorks, he has developed a browser-based set of software for cam design you might take a look at if you want to evaluate your proposed shapes. See his announcement at