Quote:
Originally Posted by TX_Dj
In my case, I just see no point in spooling the turbo (much)... more boost == more fuel... by planting your foot to P&G, are you not spooling the turbo and increasing fueling?
I've always been a skeptic of P&G (even though I've seen evidence to say it works) because well, Newton says you can't get more out of it than what you put into it... and if you put X into it by speeding up fast and coasting down, getting X as the result, that's great... but seems to me that if you use the technique of getting on the torque peak, mashing the pedal and spooling it all up for a hard pull, X > Y output... because well, it takes more power to accelerate quickly and your glide will be relatively constant from any speed all other factors being the same.
What seems to be working best for me in my truck (granted, an 8000 lbs dually is a bit of a different game than a 1.9 TDI) is to keep boost and pyro low, RPM near or just under peak torque and cruise steady rate while allowing the vehicle to slow on inclines in order to stay below target boost/pyro numbers. Then again, I'm definitely getting nowhere near as good as Dave, and he's admitted to P&G techniques. His truck is also lighter, shorter, more aero and less rolling resistance than mine.
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I'll admit that I was skeptical of P&G at first and it took me a while to get the hang of it. FYI, it depends on traffic a lot. I'm fortunate that a significant portion of my regular commute is a fairly lightly traveled 4 lane divided non-interstate highway. You can see a description of my basic technique in this thread (Post #9):
http://ecomodder.com/forum/showthrea...ear-18337.html
I'll tell you the story of one of the things that convinced me that P&G worked. Before I moved, I had 2 routes to choose from. One was the interstate, the other was a parallel highway with quite a few traffic lights. I found that even if I slowed down on the interstate, there was no way I could match my FE on the highway, even at the same speed. What I figured out was that when I was timing the red lights on the highway (by coasting in neutral coming up to them if they were red, then accelerating on green) I WAS P&G without noticing it. So what I learned to do was basically do the same thing (accelerating then coasting in neutral) more or less all the time (as traffic allows).
And no one's claiming that P&G somehow defies the law of physics. I think you're think about it a little bit the wrong way. You think the pulse is bad because it burns more fuel and burnig more fuel = bad. That's not necessarily true. Burning more fuel
overall is bad, but burning more fuel at
any given moment in time is not necessarily bad. Accelerating does use more fuel, but the conversion of that fuel to mechanical energy will happen more efficiently (if done correctly, because your engine is at higher load). At the end of the pulse you
will have burned more fuel than if you were cruising steady. But, during the glide you will make up for it.
I've made up the numbers but here's a quick axample, your engine may be 35% effecient at near full load and 25% efficient at part load (fairly reasonable numbers). Let's say you're at 30 mph. You can pulse up to 50 mph at 35% efficiency, then coast in neutral (burning almost no fuel). By the time you glide back down to 30 mph (and gotten the pulse energy back), you will be better off than if you had run the whole time steady at 40 mph and only 25% efficiency. Obviously, I'm simplifying things, but hopefully that makes sense.