Hi!

You can use the same pump for both tests, no problem. You obviously need to dimension it for the larger engine. 

For the load cell, good question! The error consists of two components, instrument noise and non-linearity/calibration drift issues.

1) The noise is insignificant. It is very small and can easily be filtered out by a suitable number in the Noise Filtering option. See the following video about instrument noise (noise filtering setting was at the lowest in this video): https://www.youtube.com/watch?v=mEHJjJzAn9s  

2) Since the smallest engine is about 10 times less powerful than the largest engine, linearity and temperature drift becomes important. The combined error of the load cell is specified to 0.03% of full scale (so if it is rated for 80hp, the error would theoretically be maximum 0.024hp). The effect on temperature is not given, so just in case you can recalibrate if the temperature is different. The effect of electrical noise and non-linearity in the electrical system is less than 0.03% and can be ignored. 

Of course, two different load cell is better, but in my opinion not necessary. The idea of two arm lengths is also ok, but note that I recommend an arm length as short as practically possible because a long arm will typically see more vibration (which translates into noise). Noise can be removed by the noise filter though.

I would recommend going for 1 load cell and a short arm length. You can always order another load cell later if you want.   

Ok, thank you for the quick reply, this sounds good to me. I used your calculator for the pump and I think this may be a possible choice?

Cross 60P061 Pump    Your thoughts?

Hi,

That pump has a great spec. It can deliver 100ml/revolution and withstand 3600RPM and 3000PSI. In theory this is good enough for almost 200HP! 

Cheers,
Jostein

OK, great, I just placed an order for all of the equipment. BTW, do you have an input for an ignition RPM signal? I use a Mychron 4 on both of my engines, it has a wire that senses the current from the spark plug wire or from an ignition coil. It would be great to see RPM from the engine AND the pump to see how the clutch is engaging and when. Thank you again for all of your work here, this is awesome! I can't wait to make some more power!

Thanks for your order!

There is no ignition RPM input signal currently. In principle you could use the second RPM input for sensing RPM from the igintion with an interface curcuit, but the software does not support it yet. It would be a nice additional feature also to be able to detect wheel slip for example, so it is on the list of potential improvements to do. But there are a few other new features ahead of it first. Stay tuned for updates!