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post #1 of 2 (permalink) Old 04-23-2013, 10:53 AM Thread Starter
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Something About UTi Instructors and "tuning"

Your gonna get a kick out of this, our class ended up having a huge debate on dyno tuning today's vehicles and including our PCM. He was discussing fuels (Course 4 Fuel & Ignition), advance timing, and air intake. His quote was "You can slap an intake, and full free flowing exhaust and only gain maybe a few horsepower (which is true for whp), then dyno tune your computer to adjust your air/fuel curve, BUT when they dyno tune your car, their programmer basically lies to the PCM on all of the adjustments during the RPM band."

He says which is also true, that stoichometric reading of an EPA emissions controlled vehicle is set to 14.7:1 ratio (14.7 lbs of air compressed to 1 lb of fuel mixture) and when their tune adjusts your ratio for 12:1 (horsepower increase), the PCM will adjust after the pulls after time back to EPA standards (FALSE statement there). I debated and argued and my quote was, "So if your saying this is true, then if an update to our PCM is needed by a licensed GM technician, his computer will do the same thing for this type of tune, resulting in re-calibrate to the 14.7:1 ratio." He then said that my statement was not true cause the dyno tuners use a different program setup and I said "How so? A program is written in one language and can be modified based on the programmer." It just got worse and worse and I felt like I lost about 20 IQ from that whole shpeal.

The problem with tuning your car from my gathering is that it may cause Emissions problems down the road, but only a WOT (wide open throttle), in which the dyno tune is performed only on.

Whats your thoughts?

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post #2 of 2 (permalink) Old 04-23-2013, 12:26 PM
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Ok, as a UTI graduate I can tell you this. You are right now probably going through the Hot-Rod-U course right? If not, that's random to have a discussion about dyno tuning and not be in that class.

You forget, the instructors there are supposed to teach what the industry wants you to teach, not what others have "hacked/decoded" in PCM/ECU programming to adjust values that were set forth by the manufacturer.

There actually are some PCM/ECU programs written now days by the manufacturer that use what is called a "learning" computer. It will automatically after a little bit of time re-adjust the tune to your driving style/needs. Thus if you baby your car, it will automatically de-tune your computer to give better mpg, where as you drive it like you stole it all the time, it will keep the aggresive tune that was set forth by the tuner.

Now the learning tunes can be adjusted so they will only de-tune to a certain point, and a lot of tuners will adjust that so it will only detune by a maximum of 1%-3%, this way it will keep the aggressiveness but still get better mpgs while you're not racing.

Now as far as what he said that it will automatically go back to where it needs to be, yes and no. Read above paragraph to know that.

The 12:1 is not a horsepower increase, but a fuel increase. It richens the mixture of fuel to help compensate for the added amount of air that is taken into the engine (basically anything lower than 13.5:1 is only generally seen on FI cars).

Now as far as the WOT comment, that was false. When your car goes into WOT mode, (most people don't know this) but your STFT's or front 02 sensor is no longer active. WOT will only allow the vehicle to read the MAF/MAP, and the rear 02's, and it will try to guess the proper fuel mixture needed to make the engine run properly (keep in mind that's why there is so much tuning involved in fuel and air tables). Most all of Dyno tunes are done at WOT, which is why they make much better power, HOWEVER, a dyno tune is NOT something you want to have when you are doing auto-x or anything that involves other things besides WOT all the time. Street tunes are much better for DD's as well as road courses, because there it's not all about how much power you make, but how fast and where you make it at.

Any questions?

I'm not degrading UTI by saying this, please don't get me wrong, but as someone who has studied performance/race cars before and after UTI as well as owning my own successful performance shop tuning a few people over the 800whp mark safely, I have a lot of knowledge and experience with this area. Someone like me who has studied this exact area for years and have worked in this area for years as well, it helps me be able to tell when others haven't been doing it that long, or are just quoting textbooks.

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Last edited by Leveecius; 04-23-2013 at 12:28 PM.
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