Quote:
Originally Posted by Ernie Rogers
I worked with Kerma last summer to attempt to improve the fuel economy of my Beetle TDI, by "chipping." We did not find a change that improved mileage. Injector nozzles were changed also and that gave no noticeable improvement.
Ernie Rogers
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Really? I have Kerma tuning also, and I would definitely agree that he is not the premier TDI engine tuner. I noticed a definite improvement in mileage from the bosio PP520 nozzles, but nothing concrete from the engine tuning. But I think it helped, especially in conjunction. There are logical reasons why altering the engine calibration can affect mpgs. Some of them are trade-offs for emissions though, which is kind of a selfish adjustment to make. On the other hand, trading total carbon emissions for a little NOx is worthwhile to some (depending on the magnitude!).
The nozzles provide better atomization of injected fuel and that should have a direct benefit on combustion.
If you drop the EGR rates way down, you get way more fresh air into the cylinder. Assuming you've started from a relatively high EGR %, this improves combustion efficiency. Also, if you have more fresh air coming in, you can reduce the amount of turbo boost required to get a certain combustion efficiency and thus engine power output. Less requested turbo boost means lower exhaust manifold pressure means less pumping losses, which should directly translate into better mileage.
Advancing the injection timing should also have a definite effect upon power production for the same amount of fuel injected. Trouble here is that most modern diesels come pretty well optimized already. If you inject too soon, you will not make more power.
Finally, pushing the engine to a higher overall power output can help you to accelerate through the higher BSFC portion of your engine map, and make it possible to run more extreme gear ratios and still be able to accelerate. Do this at your own risk however!
What no one seems to be saying yet in this thread is that you can't just lean out the air fuel mixture on a diesel and expect MPG benefit. Lean out the mixture and all you've done is REDUCE POWER! If you leaned out your entire engine operating map, to make your vehicle travel the same speed down the road you would just put the pedal down further and get back to the same amount of fuel to make enough power. This is why diesels don't have much room to improve (via tuning). In a diesel the amount of fuel injected is directly proportional tot eh amount of power made (assuming reasonable injection timing and air/fuel ratios).