DC generator braking for engine dyno 2

[sacem1]

I have posted this also in mechanical engineering other topics thread, but in case you haven't read it here it is for you:

I am planning on building an engine dynamometer so that power changes due the modifications done to my aircooled VW engine used in my self built tubular dune buggy can be determined.

There is no dyno service around here and the equipment is going to be used only on my car and several friends who have similar buggys.

We need to be able to buid it at almost no cost so I'm planning on using several pieces of equipment I have around my shop.

I have a big 100 Kw DC generator which I would like to use as a brake for the engines, use an old VW transaxle as a support for the engine with the spyder gears in the differential blocked so I can go to 5,000+ rpm's and make the generator spin at 3.88 times less using the gearcase and transaxle reduction.

I'm planning on mounting the DC generator on a support that allows it to tilt because of the torque transmited by the engine, read the weight that is being done on a side support with a known lever and read from there the torque that the motor is transmitting. Am I right?

If that is correct then the rest would only mean that I need to do some math and develop the power at a given RPM, however for it to work I need to increase the resistant load on the generator at each rpm setting until the engine starts to bog down and thats the max power at the particular speed, again Am I right?

If so can any one help me in suggesting a cheap way to vary the load at the generator so that I can make this work.

The alternative is going the inertia wheel type dyno but for the power transmitted (up to 120+ HP on 2,170 cc double carb engines) the inertia wheel requiered is big (around 48" diameter and 4" thick for a 10-15 second aceleration) and I like more the brake type dyno readings.

If this does not work can any one give an idea of how to build a waterbrake to replace the DC generator.

Thanks for the help you can give me.

Regards

SACEM1

 

[patprimmer]

SACEM1.

I always used quite long duration cams and found that with twin carbies and direct fuel path from accelerator pump to the inlet valve, torque and response was much better than the size of the cam would suggest.

This was all some time ago, so I do not remember all the details.

I think the heads you have are better than the castings available when I played with VWs, ie late 60's through to mid 80's.

I lived by the books you mention.

On the midget, we used Scatt heads and crankcase and dry sump oil system, but that had a very different budget to the daily drivers

Regards

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