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Old 05-16-2019, 03:10 PM
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First of all, of course you include the reduction from the CVT when figuring gearing on gokart or buggy. The above statement doesn't make any sense. That's like saying you don't include the transmission or axle ratio when figuring the gearing in a car.

At 3600 RPM, IF THE TC SHIFTS TO HIGH GEAR, the buggy should be traveling 62 mph. Do I think you are going to get that heavy buggy moving 62 mph? Probably not. So either the TC isn't going to fully shift out or you are not going to rev to 3600 RPM.

So I do agree that the gear ratio is not optimal. Like KartFab mentioned, a more reasonable speed would be around 40 mph at 3600 RPM. That would be using a 4.8 :1 sprocket ratio. 5.4 :1 would be even better.

---------- Post added at 04:10 PM ---------- Previous post was at 03:50 PM ----------

Originally Posted by 67StingrayJ View Post
I'm going to take your word for it, but I really wish someone could tell me why. Again, I'm not trying to be difficult, just looking for solid reasoning. As they say in the Show Me state, "Show Me".

What's the difference if had a clutch instead of CVT where there was only engaged (at 1800 rpm), or not engaged. If I had a 7.5:1 ratio in that regard, how is it not acceptable to the initial gear ratio I have now?
Let's assume a 7.5 :1 sprocket ratio with regular clutch and 18" tires.
If the clutch starts to engage at 1800 RPM, then the vehicle should be traveling 13 mph at that engine speed. If we include the fact the clutch is not FULLY locked up until an even higher RPM (say 2500 RPM or so), then we realize that the clutch will be slipping until the vehicle is traveling around 18 mph. The clutch will be slipping, getting hot, and wearing out when you are traveling at speeds less than 20 mph. So if you stop and go often or cruise around at low speeds, the clutch will wear out faster than if you run at high speeds on long open roads for extended periods of time.

Now if we switch the regular clutch with 7.5 :1 sprocket ratio to your TC with 3.1 :1 sprocket ratio, not much changes on the low end. But now, at lower speeds, the belt (or possibly the driver unit internals) will be slipping instead of the clutch.

If we look at the top end, the regular clutch with 7.5 :1 sprocket ratio would be traveling 26mph at 3600 RPM which is very doable (even with a heavy buggy).

3600 RPM with 3.1 :1 final drive ratio would be 62 mph. Not very likely for a heavy buggy. So like I said in the previous post, either the TC isn't going to shift out completely (meaning you are going to stay in a lower gear at all times) or the engine isn't going to rev to where it is making peak HP. The point of the TC is to keep the engine at the RPM where it is making peak HP at all times. In order to keep the engine at peak HP RPMs, the TC will stay in lower gear. This limits the range of the TC and somewhat defeats the purpose.

I see many people giving advice who have zero experience with "big blocks" and/or 40 series torque converters. My heavy buggy with 420cc, 40 series TC, and 18" tires has a 5.45 :1 sprocket ratio (60T :11T).
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