VC 625 rpm range

[slonomo]

Originally Posted by oldphart

The way I always clutched a drag sled, the primary is simply a governor. If engagement is where you want it, and max rpm is where you want it, leave it alone. I think this is revving higher than it should....but I'm not sure. More weight = lower rpm.

I also may be injecting a lot more science than necessary. 23 hp & 4000 rpm is a lot different than 140+ and 11K rpm.....

Jim

Gottcha.

Well yes low rpm 4 stroke single cylinder engines are much different than two stroke high rpm twins, for sure.

On a golf cart, the primary is setup for low rpm engagement, usually less than 2000 rpm. The secondary clutch is what controls the upshift profile. I think it's the same in a sled, but much different rpms etc. So if what you are wanting is less rpm at engagement/take off, then yes more weight would do that, however, I don't think you want to be less than 1500 rpm because that's just off idle and the powerband of the 4 stroke gas engine doesn't really kick in until 2200-2500 rpm. The result would be a slower accelerating machine. What you want is to get into the powerband as quickly as possible and stay there for as long as possible under load. Without a load, you want to hit 1:1 gearing right at the peak of the powerband. Once you're shifted out/fully shifted, the rpm of the engine is providing the speed from that point forward. Add a load and the rpm will drop to where the powerband is. That's how a CVT works, it does the shifting for you and should always keep you in the powerband, if it's set up properly.

If you want more rpm at takeoff, lighten the weights. But this will cause a more jerky start. Ok for drag racing, not so ok for putting around at the campground.

If you want it to upshift sooner, you might want to look at the secondary clutch and spring. Is it stock? Usually with a big block in a cart, the rule of thumb is to use the stock secondary with a stock spring and a heavy duty drive belt. Check the secondary and see what kind of setup you have there.

That 625 is a different beast. It's designed for low rpm torque, hence how people are doing wheelies. The torque curve probably flattens out pretty quickly. That's the opposite as what a sled engine does. So maybe it's setup right, you just might be used to high rpm power etc?

[oldphart]

It got warm enough today (almost 70) that I was able to do the final wet-sanding on the body for my cart. Trailer bunks on my race boat trailer were just right to use as a work stand. Hopefully....it'll be shiny in a few days. No more freakin' maize and blue.....

Jim

[oldphart]

I dug through leftovers on the shelf.....and found a bunch of odds and ends of red urethane basecoats. This is what I ended up with after I mixed 'em all together and put 'em in the shaker. It's getting closer to done. Pardon cluttered shop & booth. It was antiseptically clean when I made a living in it.

[oldphart]

It's finally finished other than carb and clutch tweaking......unless I decide to change gears. I'm still kicking that around.

Thanks to all that helped out with advice & info.

Jim

[slonomo]

Looks good! Are those hydraulic discs too? Nice!