Calculation

[84-1074663779]

There are many different ways to measure engine power for tuning and development, but for some of us a lot of these are either too expensive or not practical.

I will never be able to build a home dyno because of the noise it would produce and the closeness of neighbors in a (snobby) residential area. But for a road car, there are other ways.

The easiest is by data logging and doing full throttle acceleration runs, and using software to plot torque and power curves on your home PC. This has its limitations though.

Another possibility is to use a Telma eddy current retarder built into a small trailer towed behind the vehicle. You could hold the vehicle at full throttle at any desired RPM, and read draw-bar pull. If you can accurately record road speed as well, power and torque calculation is easy.

The main advantages are that you can do all your testing on a quiet back road somewhere well away from neighbors, and a dyno trailer would be very easy to construct. It could do everything a chassis dyno can do. It also has the advantage of proper airflow around the engine while on the move, sometimes a big problem on a chassis dyno.

I have not built one, and probably never will, but it is just presented as a nutty idea that just might appeal to one of you guys.

[Greg]

Tony,
Have you seen superflows towing dynos?



Only problem is that your car needs to be registered and have a towbar.

What would the power requirements be like for say one of the Telma retarders in a towing dyno, I spose you could easily set up a trailer with a differential and run it on the front of that?

[84-1074663779]

Fitting a hidden or removable tow-bar to a registered road-car is not really going to be a problem. For some of us, a dyno trailer might be a lot more practical than a permanent chassis dyno.

If you are renting or leasing property, digging a pit for a chassis dyno might present a bit of a problem as well (chuckle).

As far as building a dyno trailer goes, you could get a Telma that has a pair of drive flanges for fitting into a trucks split tailshaft. Solidly mount the Telma to the trailer frame, and build an independent suspension for the trailer. This would give minimal unsprung weight and maximum traction on slightly bumpy surfaces. A bit of concrete ballast might be needed, depending on how much power you have.

One of those over-run trailer brake couplings could be modified to measure drawbar pull. A brake master cylinder with a pressure transducer should do the trick. It would convert drawbar pull to an electrical signal pretty simply.

[Sandra]

How should I calculation the power on ny rolling roade?

[Tony]

Hp = Rpm x Torque in foot pounds divided by 5252

[rab]

Are you calculation the RPM's from the motor or the roller??

[Tony]

If you are measuring torque at the roller, then roller Rpm is used.