Piston Slap: Factory Tune, Power On The Table?

Sajeev Mehta
by Sajeev Mehta

TTAC commentator Raph writes:

Hey Sajeev I’ve got a a bit of a conundrum with 09 GT500. I recently purchased a blue-tooth OBDII dongle and the Torque Pro app for my phone which provides a variety of useful functions including monitoring various PIDs (On Board Diagnostic Parameter IDs).

While checking over the various PIDs I noticed the throttle body was limited to 75% of WOT and I’m not sure if that was just a limitation of the app or perhaps the tune was limiting the range of movement on the throttle body?

Also I noticed that the boost inferred by the car’s factory boost gauge does not correlate to the boost reading in Torque Pro? The Torque Pro app has an adjustment feature to scale the boost reading by either setting it to zero, a positive value or 14.7 psi or a negative value of 14.7 psi.

I’m unsure how Ford references boost with the MAP sensor since fiddling with the scale adjustment in Torque Pro hasn’t produced any worthwhile results (a best 4 PSI but the blower on the car is pullied to produce in the neighborhood or 18 psi.

Long story short: Am I leaving some power on the table and what about that damn boost reading?

Sajeev answers:

Whoa duuude, you mean that the fancy smarty-phone app says you are only at 75% throttle when you floor it?

We’ve been down this road before, as these apps often read parameters sans the accuracy of tools available to powertrain engineers or even shade-tree tuners with EFI hacks. While it’s been proven many times over that the GT500’s stock tune is pretty conservative, it surely ain’t 75% throttle conservative. As much as I love new tech, while my career revolves around Web 2.0, we need a reality check: sometimes apps aren’t that awesome, they can kinda suck.

To wit, I sent your queries to a real tuner, Mr. Torrie McPhail, who is both a trusted friend and a well-regarded dude in the tuning world. This isn’t an endorsement (even if it is) because I can’t possibly know the stuff in Torrie’s brain. So let’s do it, to it:

“First point: what calibration is in use? If you are using something non-stock, I would request calibration information from that source as to vehicle output.

I doubt anyone would be limiting throttle angle on a car like this, most likely that is how the phone app construes the PID output while at WOT which would put it squarely in the shadow of the shaft anyways.

And the factory boost gauge isn’t actual and just calculates inferred manifold pressure from sensor output. I would stick a good Autometer boost gauge in the car to solve that.”

So there you have it: if you have a stock tune, you are leaving PLENTY of power on the table, even a conservative tune will unlock plenty more power. And don’t take the engine app too seriously. Off to you, Best and Brightest!

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

Sajeev Mehta
Sajeev Mehta

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  • Eiriksmal Eiriksmal on Sep 24, 2014

    *grumbles* The domestics get such a sweet community of tuning. Nissan's largely left in the lurch. Er, I mean, "Nissan pushes their engines closer to the limits, so there's not as much to be gained from a simple tune."

  • Cbrworm Cbrworm on Sep 29, 2014

    UPRev has decent tunes for some Nissans. Mostly 3.5+ liter ones.

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