Accuracy of efilive's dashboard dyno

[slows10]

Hi, wondering what you guys think of the accuracy of efilives calc. RWHP compared to a rear wheel dyno. I understand both are simply tuning tools. When people post their hp numbers im assuming its usually from a rear wheel dyno. So can I compare my calc RWHP numbers to a rear wheel dyno? What are your thoughts or opinions on this? Thanks

[WeathermanShawn]

If you are talking about the CALC.RWHP which is taking Vehicle Weight and change in VSS with time..I think it is pretty accurate in what it is describing, but will fall about 20% short of a Dynojet reading.

I think of it more in terms of 'Net Horsepower'. Similar to the way G-Tech computes HP. Net HP basically takes in weight, aerodynamic drag, parasitic HP loss, etc. I am sure one of our Engineering experts can elaborate.

I use it for comparison purposes only. I use it to compare Winter to Summer runs, and see if a Spark or Fuel change will register any significant HP change. Similar to just running consistent 1/4 mile runs after another..

Thats my take..

[joecar]

CALC.RWHP uses the physics definition of power P=m* v*dv/dt and converts from Metric to Imperial.

P = instantaneous power
m = total mass of vehicle and contents
v = instantaneous velocity
dv/dt = instantaneous acceleration

P is accelerating the vehicle after all the losses have been overcome (mechanical friction, aerodynamic drag);

i.e. after balancing out all the losses, P is the remaining power that is increasing vehicle velocity;

P will be different than what you see on a chassis dyno since the losses will be different, the chassis dyno allows velocity to increase at a different rate than driving down the road does.

If you/conditions are consistent (i.e. good technique) you can use CALC.RWHP as a mod comparison tool.

You can obtain the combined losses by coasting down from some high speed and noting the values of negative power at each mph point; you can then subtract this (subtracting a negative is same as adding the positive) from the power at each mph point obtained from accelerating... if you have good technique then you will get values that are close to FWHP.

[slows10]

Thanks for the replys. Ok, so its fair to say its more conservative than say a dynojet. Im not using it for bragging rights, but as a tuning tool as the weatherman said. Im seeing how my fuel and spark adjustments change this number. Im running a 4 cylinder s10 with a t3-t4 13lbs boost. I was pretty surprised when after one of my last runs and many many changes this thing hit 232 hp according to efilive. This was at 112% duty cycle on the injectors. I thought this was fairly generous. But maybe not. Time for more injector

[slows10]

Thanks joe ill try out that technique you said.

[slows10]

Any chance the guys at efi live would add some kind of injector size adjustment on this pcm? I think they call it injector flow rate. What a pain it is trying to tune this without being able to use the injector spread sheet.

[joecar]

Post your tune file or a pic of your IFR table, the IFR calculation is simple (can be done without spreadsheet).

[slows10]

Joe what im saying is there is no IFR table for this pcm.

[joecar]

Which PCM and which OS is it...?

[slows10]

the pcm SERV# is 16228016 the HDW# is 16204850 the o/s # is 09356824. Thanks