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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > Engine Tunes/Mods

Engine Tunes/Mods Performance Engine Tuning/Engine Modifications

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  #1  
Old 01-27-2019, 12:02 AM
Calion Calion is offline
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2003 Chevy TrailBlazer LT EXT
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Question How can MPG tuning possibly work?

Forgive me if this has been addressed before; I ran a couple of searches and couldn't find anything.

How can tuning for MPG while increasing performance, as PCMForLess, Wester's, and Wait4Me all apparently claim to do, possibly work? How can somebody hook the PCM up to a computer and do a better job than GM's professional engineers can? I can see that they could choose a different tradeoff—more towing-focused, or more get-up-and-go, or more MPG (at the cost of umph) could work, but that's not the claim that I have seen many times on this site. The claim is that the truck has more pep and better MPG. If it was that easy, why doesn't it come that way stock? Are these guys smarter than GM's engineers? What am I missing here?
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Old 01-27-2019, 08:24 AM
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TB-Al TB-Al is offline
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Everything is a compromise. One simple way is to advance the spark and you get more power from the same amount of fuel. You also cause more engine knock and wear out the bearings faster. Lean out the fuel/air ratio might get your better mpg with the same power at the risk of burning valves or even putting a hole in a piston. Buy a bunch of snake oil if you want but I'll stick with what GM research thought was the best compromises.
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Old 01-27-2019, 09:12 AM
Calion Calion is offline
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Quote:
Originally Posted by TB-Al View Post
Everything is a compromise. One simple way is to advance the spark and you get more power from the same amount of fuel. You also cause more engine knock and wear out the bearings faster. Lean out the fuel/air ratio might get your better mpg with the same power at the risk of burning valves or even putting a hole in a piston. Buy a bunch of snake oil if you want but I'll stick with what GM research thought was the best compromises.
Interesting. You're the first one I've seen to speak against tuning. Every other of dozens of posts have nothing but praise.
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Old 01-27-2019, 09:27 AM
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TB-Al TB-Al is offline
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Of course most people thing they can improve on what the experts design. Put a 750 hp engine in there and you will get a lot more acceleration even if you don't change the transmission or differential. For the first few days you might brag about what a great modification it was. Will you be back later to admit it might have been a mistake? What if it takes 2 years for your engine to fail? They aren't making huge changes that would blow up an engine immediately because word would quickly get around and that would be the end of their sales. And since they are small changes, maybe if you were only planning on keeping the vehicle for a year these changes might be beneficial to you even if not to the next owner.

I just know from experience designing equipment that everything is a compromise. If you make one thing better you make another worse. So you try to optimize the package for the best overall performance. Start tweaking that and you are designing a different machine for a different use. And without all the supporting data for the things that will get worse you may just be creating a much worse outcome.
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Old 01-30-2019, 09:44 PM
RPatton76 RPatton76 is offline
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I don't know how much this is done, but the factory tune can be leaned out somewhat, which increases NOx emissions, but increases mileage. This is how VW got great mileage and long lasting exhaust emissions things: they kept them off much of the time. Factory programming doesn't want to let the NOx emissions get high so they don't get all the mileage they can out of it. But, retarding the intake cam (if it were adjustable on our 4.2L motors), would make it more fuel efficient by making less power. At any rate, one way to increase mileage. If I could, I'd phase the intake cam to about 106 degrees for more low end torque since we tow occasionally.

Rob in AZ
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