Dyno app.

[Nate S]

Was looking for something else on my iPhone and came across "PerfExpert", an app for 0-60, 1/4 mile -and- dyno. So I dropped the $12 and got it. Most of the shitty apps of this sort use the gps alone and not surprisingly they aren't too accurate. This however uses the three accelerometers in the phone and does a great job. Works best with a manual tranny of course but should be fine with an auto above the stall. You plunk in all sorts of info and get on a straight, flat road. Start at zero and get to the bottom RPM of the gear you're testing in and floor it through the gear. App does the rest. A quick test in my stock Tacoma has an HP curve identical to the factory published curve. Lots of data out there on people with identical app and dyno curves. Looks like some fun to be had here and a great way to test tuning. Corrects for atmospheric conditions too.

Maybe this weekend I'll try it in the Plymouth.

These are from the app and some dyno info from the factory. I obviously took my foot out of the gas earlier than they did. Anyway, a neat app and accurate. Obviously measures wheel hp and has a converter (about 18%) for engine HP. You can add whatever you want for gross hp manually. Website will even let you lay one chart over another for comparison.

 

[Nate S]

So, I took out the Sport Fury and tried it. Came out exactly as I expected. 290 hp (net). Did a few runs and all were pretty close. Figure a ‘71 440 hp was 305 and this has 20 ci less. Beats dragging the thing to some dyno for the same result. Little hook on the left is the end of the torque converter multiplication.

 

[BSB67]

That's pretty cool. What are your inputs? You think it is a net actual hp?

It would be nice to correlate it to actual track data.

 

[Nate S]

That's pretty cool. What are your inputs? You think it is a net actual hp?

It would be nice to correlate it to actual track data.

You put in weight, tire size, gear ratios, fuel tank size and a variety of other things. It calibrates the accelerometers in the phone. Super easy to use. There are some European car guys who have done A/B with a chassis dyno and got identical results.

It will provide wheel hp if you want it. I think the number I got is legit.

 

[BSB67]

I was curious about the net actual (uncorrected) flywheel hp. It probably derives it from the RWHP.

 

[Nate S]

I was curious about the net actual (uncorrected) flywheel hp. It probably derives it from the RWHP.

Oh definitely. I think it figures you lose 20% to the drivetrain.

 

[PRHeads]

How does it determine what the engine rpm is?

 

[Nate S]

Tire size -> diameter -> rotations per mile x axle ratio x tranny ratio x speed/60. With the auto I added 10% to the axle ratio for full throttle slippage. That came out just about perfect. The app calibrates at a dead stop before you go and uses the accelerometers to know the actual speed (to use in the calculation). Down low where the torque converter is multiplying of course it’s wrong. With a manual tranny it would be very accurate.

There’s an option I didn’t use to pick a speed at xx rpm instead of the ratios. For a manual that would be accurate, would need to add slippage for the auto.