Vacuum gauge instead of Scangauge?

[GasSavers_StanleyD]

Originally Posted by Jim Dunlop

OK, so if I understand those shortcomings it can be a benefit to me.

I am still having difficulty understanding, from a physics equation standpoint, how P&G can be better than constant cruising speed. Unless of course it has to do with "tricking" the PCM somehow, or that people think it helps because they spend some amount of time at a lower speed, or that it makes the Scangauge think you're getting good FE.

My gut instinct would be that constant speed trumps ANY amount of acceleration in terms of the amount of fuel to get from A to B.

Personally, I think that one of the biggest things that P&G overcomes is ENGINE DRAG. Engine drag is the drag that is associated with the engine being in gear. If you understand manual shiftthen it will be easier to understand. Imagine going 50mph in 2nd gear in your car. Your car actually CAN go 50 in 2nd gear, but its not a good idea because you are making the engine race and getting VERY poor FE. Furthermore, as soon as you let go of the gas pedal the car will quickly slow itself down because the car does not naturally want to rev at a zillion rpm. The only way you can rev that high is by FORCING the car to rev high by flooring the pedal. A speed of 50mph is more suited for 4th or 5th gear, although 2nd gear can attain it, just not as efficiently.
Well now imagine doing 80mph in 5th gear. Just like a car can go 50mph in second gear, a car can go 80mph in 5th gear. Just not a good idea and with poor FE. Speeds of 80mph are more suited for errrrrr, lets say 6,7, or 8th gear. Hence are problem: I dont know about YOUR car but my 98 Camry doesnt have an 8th gear I can only get 80 mph by really pushing the pedal. As soon as I let go of the gas pedal the car immediately slows down trying to reach a more reasonable and comfortable rpm. By going 80mph I am fighting the cars natural inclination to not race and run at an equlibrium rpm.
SOLUTION: Anytime your car is at a speed where the engine is racing, it is trying to slow down but we fight against the cars tendency to slow itself by pushing the pedal and forcing it to go increase rpm. So once you force a car to go 80mph, just free the car from any gear and let it GLIDE. It no longer wants to slow itself down. The only force working against a gliding car is wind resistance, tires, ect, BUT NOT the engine.
No one will go 50 in a stick shift and downgrade into 2nd gear if they want to slow down to 20 mph unless they want to do it quickly. They will go MUCH farther if they go 50 and just remove the car from gear and let it GRADUALLY slow down. Once the car reaches 20mph, they will re-engage the gear. Well thats exactly what P&G is. You reach a speed that the car will not naturally move at and then let it slowly reach a slower speed. Dude, just drive at 60 to top of a gradual incline and then record speed at bottom of hill. Then do the same experiment BUT put the car in neutral just before you start going downhill. I bet any dollar amount that speed at bottom of the hill in neutral will be HIGHER than when car was in gear. Neutral driving is better for car than in-gear driving. Thats big advantage of P&G. If you are gliding for half of your drive then you are subjected to engine braking for only half your commute. Imagine if we could get rid of aero drag for half our drive. . I know this was long explanation, but I hoped it helped. Any oppossing comments welcome. Im here to share and learn just like anyone else. If Im misleading Jim then I wanna know cause Im also misleading myself. Good luck !!!