It is not only useful to count up the horses, but also to dial in the engine to get maximum out of it and find out what needle to use, what advance to use and so on.

I believe there is a (fairly cheap) DIY solution to this too. In our country with long and steep descents from the mountains there is a much used brake option on many of the big trucks and some buses. It's called a "Telma" brake. This is a unit that is put inline with the shaft going from gearbox to rear end. It works by setting up a magnetic field between a rotating and a static assembly. This can be done in several steps by energizing coils through application of a DC current. If you take an old dynamo, short the output and try to turn it, and you will feel it is braking. (This is just remotely similar to the actual Telma implementation).

A Telma has only few parts that wears: the bearings. So an old unit would easily recondition to be as good as a new one.

It can be had cheap from breakers. I've seen £200-£300 mentioned. I don't think they usually install old units to new vehicles.

They can burn off a lot of power. They must, as they are supposed to contribute most of the braking power to hold back a vehicle and trailer with a combined weight of 50.000 Kg going down hills with altitude differences of around 1000m in one descent, and sometimes quite steep too. If they (together with exhaust brake) are not capable of holding down the speed, cost goes up, as the brakes must be used, and they wear down. I would hope it to take 300HP during short bursts, and between 100-200HP continous. But for a Mini engine less would do fine.

Making one of these into a brake bench will involve:

1. Test rig frame with:
   1. the Telma unit suspended to rotate slightly (a few degrees) around the axis of it's in/outgoing shaft.
   2. A "leg" sticking out from the Telma, resting on a load cell (Note 1).
   3. Mounting pad on the frame for the other side of the load cell.
   4. Cooling fan(s) for forced air cooling of the Telma.(Note 2).
   5. Part of the frame protruding in one direction to take a mounting "buck" for the Engine Under Test (EUT).
2. Load Control Unit for dialling in the braking force of the Telma.
3. Sensor Unit for converting the output from the load cell to some useful output device. This may be anything from a needle instrument to a computer (preferred).
4. Accurate revcounter. It should preferrably be mounted on the Telma to avoid having to interface to different engine types.
5. Well balanced axle with 2 universal joints for connecting EUT output shaft to Telma.
6. Engine buck. This one should be made to bolt down to the test rig frame fixing the output from EUT inline with the Telma axle.
7. An adapter to mate the EUT output shaft to the universal joint. (Note 3)
8. Sundry adapters and fittings for cooling water, air circulation for oil cooler and intercoolers. Exhaust extraction and muffling. Throttle cable with control handle.

The mechanical items should be fairly easy to make by anyone that has done some cutting and welding with a bit of precision. For item 7, some lathework will be involved, but even farming this out will not cost you many beers.

Items 6 and 7 and in part 8 will be needed for each engine type you intend to test.

Items 2 and 3 will need some resources that may not be available to a lot of you, but it could be made general enough to be reuseable for several builders of this beast. I don't see that it would be complicated or very expensive. And I know there are others on the list beside me that could do part, (or all) of this. (Hey Scott?) I won't describe this in detail here, as there are many ways to skin a cat.

Accuracy of this rig will be dependent on:

1. Accuracy of the load cell.
2. Accuracy of the revcounter.
3. Low friction of 1A.
4. Correction for cooling fan load. See note 2.
5. Correction for internal aerodynamic drag in Telma. I don't know if this will be significant, but it can be measured and corrected for.

The above outlines a MkI version. Further refinements could later be added in stages when/if time/desire allows (Mk):

1. Integrating 2, 3 and 4 into one unit (computer), so it could spit out the HP figure without you hacking on the pocket calculator. And it would then be able to load balance the brake power against the RPM automagically.
2. Adding a servo unit to the throttle, allowing the control unit to balance everything, and so it will enable you to preprogram a full test run and spit out the verdict afterwards.

As the "Mk's" are added, the cost will of course rise, but so will the ease of use. But MkI will be fully able of giving the desired results.

At the moment I'm investigating: - What exactly will a useable Telma cost, and what will refurb cost? - Can the Telma stand 7K RPM? If not, some kind of gearing down will be needed in front of the Telma. If this is fixed to the Telma, no power correction will be needed for this. The load generated by this box will also push on the load cell and get measured. The real downside is that it will significantly increase cost and complexity. - What exactly are the power handling specs for the different Telma units? - Can the power handling be improved by alternative means of cooling? I'm primarily thinking about water mist added to the airflow. I don't think this is a concern with most Mini engines, but I need it to handle 300+ HP.