Is there any point to P&G in a diesel?

[JacobAziza]

DFCO in gear is gonna slow you down a lot from engine breaking, which isn't what you want for a coast.

I doubt from how it feels that my truck does it, but I have a fuel cut off on the gear shift lever, so its kind of moot for me.

[Christ]

Originally Posted by JacobAziza

DFCO in gear is gonna slow you down a lot from engine breaking, which isn't what you want for a coast.

I doubt from how it feels that my truck does it, but I have a fuel cut off on the gear shift lever, so its kind of moot for me.

I think the suggestion was made moreso for when you're coasting a grade... you keep it in gear, and the engine braking doesn't slow you down, it just stops you from going any faster.

[dcb]

Originally Posted by Christ

...
The nature of a manual transmission leaves all the gears engaged on each other 100% of the time.

Sorry to dredge this up, they are all touching, yes, but if it isn't in gear and the engine isn't turning, but the car is rolling, then the gears themselves are not turning (and my clutch adjustment is fine, thank you). If you engage the outputshaft to a gear then they all start spinning, including the clutch (EOC assumed, clutch disengaged) which has a noticeable effect on my coasting distance.

[vtec-e]

Originally Posted by JacobAziza

DFCO in gear is gonna slow you down a lot from engine breaking, which isn't what you want for a coast.

I doubt from how it feels that my truck does it, but I have a fuel cut off on the gear shift lever, so its kind of moot for me.

A lot more than coasting, yes.
But a diesel will DFCO further than a gasser because the gasser has a throttle plate. This drags down the speed quickly. I've tried Pulse & DFCO in my diesel yaris and it still improved my mpg, just not as much as Pulse & Glide. That's assuming my SG is reading correctly, which i think it is, after much faffing around and telling it that my engine is a 1.2 not a 1.4........

ollie

[Christ]

Originally Posted by Christ

That's because when you leave it in gear, you're also spinning the clutch disc and input shaft, and your clutch is probably not adjusted properly, and thus dragging slightly on either the flywheel or the pressure plate, but not enough to cause significant trouble when shifting, or even noticeable trouble.

Even if you're not dragging your clutch, you're still wasting more of the momentum to spin the clutch disc while you're in gear.

The nature of a manual transmission leaves all the gears engaged on each other 100% of the time.

dcb -

What part of that post had anything to do with what you said?

You said that when you left the car in gear, it decelerated noticeably fast. I was agreeing with you, and explaining (for the benefit of those who don't know) that when you leave the gear selector engaged, with the clutch disengaged, that you're still spinning the entire gearbox, thus making more friction, which explains why you slow down faster in gear than out of gear.

Sorry if I offended you by assuming that your clutch (like most others) is still dragging slightly while disengaged, because unless it's purpose built, it's not 100% true, especially after being used, and will still drag slightly when disengaged... no offense was intended.

[dcb]

Just trying to clear it up, no sweat. Neutral works better in my car, cuz no gears AND clutch are spinning. On the bike it doesn't matter much because the clutch is between the transmission and the rear wheel. Thought there was another response from someone else but can't find it now.

OB diesel P&G, I will have to test that now, somehow. Don't know how to ABA it in the TDI, except to my own satisfaction maybe.

[Christ]

Is that how all bikes are? (clutch between trans and rear wheel)

[cfg83]

dcb -

Originally Posted by dcb

Sorry to dredge this up, they are all touching, yes, but if it isn't in gear and the engine isn't turning, but the car is rolling, then the gears themselves are not turning (and my clutch adjustment is fine, thank you). If you engage the outputshaft to a gear then they all start spinning, including the clutch (EOC assumed, clutch disengaged) which has a noticeable effect on my coasting distance.

...

This sounds like what Frank Lee talks about. Ditch some in-between gears to increase his manual tranny's "total" efficiency (i.e. reduce it's parasitic [inertial?!?!?] losses). Instead of having gears 1 through 5, maybe just the 1, 3 and 5 gears.

CarloSW2

[bluetwo]

Originally Posted by cfg83

dcb -
This sounds like what Frank Lee talks about. Ditch some in-between gears to increase his manual tranny's "total" efficiency (i.e. reduce it's parasitic [inertial?!?!?] losses). Instead of having gears 1 through 5, maybe just the 1, 3 and 5 gears.
CarloSW2

Makes sense.... losing weight the engine has to turn is always a LOT better that losing weight in static positions. I think losing lbs. in flywheel weight is like losing twice that of weight in the interior for example.

Did I get that right or am I just way off?

[dcb]

hmm... well, a gear has no where the angular momentum of a fully inflated tire (lest my tranny self destruct while shifting), but might be something there. The extra gears in a 5 speed add a tiny bit of resistance (more bearings and teeth meshing). I guess you could ditch the selector forks and synchros and just slide the gear teeth together, like a reverse gear (with position sensors and computer help/rev match maybe).

But I don't know if it would buy much.