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I would look at the MT 643 or the newer MD3060 transmissions for the
first gear planetary. The Allison 1000 is the transmission used in GM
3/4and 1 ton trucks..Lots of parts and the price may be good but the
MT643 or MD3060 will give 3.5:1 ratio. That would allow 10,000RPM and
close to 3,000RPM at the prop. Get full use out of building a
different PERU.

Dale Davies

Are you sure about that ratio. Can you get the dimensions of the ring
and sun gears?

I have decided to build our own planet carrier out of 7075T6 and add
two pinions. Six total up from four. 50% more torque capabilities.

Thje parts are low cost.

Paul Lamar



Yes Paul. I found the ratios listed on an Allison web site in the
specs section. There is even one with a 4.5:1 give or take ratio if
someone wanted to use a wide cord low RPM prop for low noise. I will
see what I can find out about planetary dimensions.

Dale Davies

Not the same as the ratios of the individual planet sets. Those are
the ratios of concern for a truck engineer or customer. There is no
real reason to publish the ratios of the individuate planet sets
under specific configurations..

The same planet set can have different ratios depending on which
devices are fed power, which are held fixed  and which extract
power.

The ratios published are a combinations of the three  different
planetary's working together.

Here is some info on that.

Paul Lamar


With the horsepower you're talking about and the speeds the Sport
Class is running, I don't think running a propeller at 3000 rpm is
such a great idea. I haven't run the numbers but I would think you
want to keep the tip speed below .8 Mach.  With this speed and
horsepower, you need to think about propeller efficiency.  I once
talked to Jim Bede about an Unlimited Racer. It was configured like a
big BD-5 and there was no way to have an efficient propeller with the
horsepower we were looking at and the diameter restriction.

Steve Brazil

We are not planing on running the prop at 3000 RPM. We are planning
on 2000 RPM.

I would love to run the engine faster than 6000 but with a 3:1 planetary
that looks like the best engine speed. That means the boost will be higher.

We could use a 4:1 planetary if I could find one strong enough.
Given a six inch diameter ring gear the sun gear would have to
be only 2 inches in diameter. I would settle for 2.5 inches.
Currently it is 3 inches.

Paul Lamar

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