Tried my first P&G today

[serialk11r]

gWell just keep in mind you're using the car's mass as energy storage, but the faster you go the more power you use. Say with engine on gliding, if you were able to rev match the engine and put it into gear instantly with no fuel, then you'd want the pulse intervals to be as short as possible to keep your speed constant and reduce your power consumption to average speed ratio.

I have no idea what the best compromise between drivetrain wear, driver effort, efficiency, etc. is, I guess that's just something you'll need to experiment with to find out. Apparently 10mph speed variation works well for the people saying 55-65 or whatever.

I think leaving it in gear is not a good idea, because when you do that your engine pumping goes way up when no fuel is injected since you'll lose energy to pumping at both the throttle/intake and the exhaust (exhaust port will open when the cylinder is below atmospheric and lose all the energy it took to expand the gas below atmospheric pressure), not to mention the transmission works less efficiently when the wheels are transferring power to the engine and not the other way around. This most likely offsets any efficiency gain. If you leave it in gear, "drive with load" should be the best at least on a flat road.

[euromodder]

Originally Posted by chrisoverson

I assume to do this you'd need a car with very low drag and low rolling resistance, and switch everything off when the car is in glide mode.

Whatever helps to improve / lengthen the glide, will improve the efficiency of P&G. The glide is essentially what make P&G so efficient.

So if I start simple with an injector kill switch for glides, should I always shift to neutral and have to bump start the engine every time?

If you stay in gear, the engine compression will drag you down.
So yes, you must go into neutral.

Bump starting in the highest possible gear is preferred - better than using the ignition key + starter engine
(the ignition easily wear out on some cars, my Volvo being one of them)

[chrisoverson]

Okidoke. Looks like I have some work to do. Very sorry if I've hijacked the thread here as it was not my intention, but hopefully this will all contribute to increasing efficiency of pulse and glide.

Here's what i've just done as a test grille block:



Will test it after lunch

[PaleMelanesian]

You can rule out the ignition-on-in-gear "glide" option. It's not anything close to a glide. You're better off just running steady speed than trying an in-gear p&g routine. For a glide to be worthwhile, you need to be freewheeling and minimizing drag.

* depends on how the car handles no-throttle. Some automatics will freewheel which is good and makes for easy p&g - just let off the gas. Some hold in gear and engine brake which takes away the value of p&g unless you manually go to neutral.

[chrisoverson]

It's a manual gearbox, so I'd have to shift into neutral each time... I guess just leaving it in gear is a no go then.

The car glides less when in gear, so I won't get max MPG... but would pulsing and gliding still be an improvement? It needs further testing.

[PaleMelanesian]

With a manual, p&g is better, even if it's engine-on p&g. Many of us here have tested and demonstrated that.

[Sven7]

In gear vs. neutral gliding are night and day difference. You can actually "measure" it with your eyes and your butt-o-meter. Just coast in neutral.

[chrisoverson]

Ok, just tried out my temporary cardboard grille block. For anybody who's interested, I've put all the results on the MG-Rover forum here: The Super Efficient 1.8 project - Page 4 - MG-Rover.org Forums

I'll definately stick to the engine in neutral but idling technique for the moment, as I want to see how I can reduce fuel consumption on idle. The hot air intake certainly seems to contribute to this very effectively.

[euromodder]

Hawk the engine /coolant temps with the grille fully blocked, until you're sure it doesn't overheat with the block.