sun dyno questions  


I have a couple of questions in regards to a Sun Ram 12 Dyno I have upgraded using Your Dyno

1 It would appear that the dyno may be reading low 10-15%?

2 In manual control The dyno holds the set hold rpm nicely but in Auto ramp it is slow to pull back to start rpm and is always hold 200-300 higher than what the start rpm is set to.

3 is there away to set a start roller speed instead of engine rpm as vehicles with autos and  high stall converters are very proving very hard to set an accurate gear ratio.

4 I have fitted a Dtec rpm input but are finding that I'm forever having to change the response time links in the Dtec unit, and therefore i have stopped using it.Has anyone else had this problem?


some basics about the dyno

its setup as a brake dyno with a 500kg load cell

440mm arm and calibrated with a 29kg weight

MOI= 9.7

Roller circumference =1000mm

any help with this fine tuning of our machine would be a big help. Other than that we are loving the upgrade.





Posted : 24/07/2019 10:33 am
Member Admin


1) For the low reading, it may be your MOI is too low? You need to include the MOI of the drive train including the wheels.

Note that wheel HP is what we measure. Engine HP is calculated using wheel HP plus drive train losses. However drive train losses are impossible to measure. We can measure it during coast down, which is what we do, but the losses are higher at full power (that's why high performance cars have cooling on the transmission and diff). YourDyno shows Engine HP = Wheel HP + drive train losses at coast down. There are no fudge factors added, but you are free to add one either as "Additional horsepower correction" or slightly higher MOI. 

2) Auto ramp; do you mean Power Sweep? It should hold the start RPM accurately. It may overshoot somewhat first, but shall definitely go down to the start RPM during the waiting period. If not the Ki is too low. 

3) Yes, indirectly. For Autos with no fixed gear ratio you need to use Results vs Speed and can only look at HP, not engine torque since it depends on gear ratio.Gear ratio can be set anything. You can do a quick calculation to find which gear ratio is suitable. Using Speed (km/h) = (Engine RPM / Gear ratio) * 60 (min/h) * 0.001 (km). Use 0.06 as gear ratio and speed (km/h) as start/stop condition. 

4) OBD2 is a much better option. 

Posted : 28/07/2019 11:35 pm

where do you set "start/stop condition to speed ?


Posted : 14/08/2019 10:17 am

sorry I miss under stood , I get it now





Posted : 15/08/2019 11:33 am
Select your currency
EUR Euro
USD United States (US) dollar