The Official 356Talk Forum

If you stretch or compress either the power line or the rpm line of the graph the line plotted gets more or less jagged. The same engine will look different depending on how the graph is proportioned vertical vs horizontal.

Here are the actual numbers to compare which might be easier to understand. Ignore the hand written notes.

Thanks, Cliff. Clearer to me now.

Mike

I'm sure you all know this already, but the only dyno comparisons that are meaningful are those done on the same dyno the same day (e.g. various runs for carb changes, etc.) There are (at least) two fundamentally different kinds of dynos as well. The traditional kind that can apply an adjustable load (e.g. a big water pump) and hold any given RPM to give a torque reading at that RPM. The second uses a big, heavy roller under the driven wheels and measures torque by calculating from the acceleration of that big mass at full throttle from your min. RPM to your max RPM. This kind is much faster at collecting data, but can't hold a constant RPM. It isn't difficult to imagine that the same engine on each of these dynos on the same day would give different results. Other variables affecting comparisons are ambient temperature, altitude, humidity, etc. Many dyno operators will automatically correct readings to STP (Standard temp and pressure) but not all.

SuperFlow and DynoJet are very good at producing repeatable results from location to location and machine to machine. They both have very accurate weather stations feeding into the computer program of the dyno. Traditionally DynoJet was strictly an inertia type that measured the acceleration of a very large drum(900lbs?) while SuperFlow used an eddy current electric resistance motor to measure how well the engine fought against it. That is more like the function of a fluid dyno with adjustable resistance. For various reasons DynoJet added an eddy current option so that it could also measure and tune at a steady resistance or could be programmed for a simulated driving test. I don't know the SuperFlow well but they may now offer an inertia option.

In the old days you had very many variables that the operator had to account for that included the temperature of the fluid used to resist and accuracy was difficult.

Regardless of the dyno once you have read a number of the graphs you will know how well the engine will work in use.

Hi Mike, got those printouts today, thanks!

You are most welcome, Paul. John posted the results for everyone to see.

Mike