How do you Pulse & Glide your diesel vehicle ?

[rmay635703]

On my antique 6.2 NA diesel torque is almost constant from 1200rpm through about 2500rpm with a very very gentle curve up going to 1850 then slowly back down, drops like a rock going past 3k and prior to 1200

This means MY HP is almost linear with RPMs, I would expect turbos to gain torque as RPMs increase as opposed to stay the same, but just a guess.

In other words the HP curve would be exaggerated much more than my NA due to the turbo spooling up as motor RPMs increase.

[Arragonis]

Although I have a love a TDI driving an NA diesel is also a fun challenge in itself. Rob's NA 1.9 Polo is a case in point. Its the need to balance throttle against what the engine can take to get the best out of it.

The best explanation was in the old Diesel Car Magazine, before it was turned into the naff magazine it is now. The theory at the time was that if you floored it you just pumped loads of extra fuel into the cylinders, a lot of which couldn't be burned efficiently so you actually got no more power but used a load more fuel. Think of it like smothering a lounge fire with too much coal, the air flow to the burning bits is not enough to be efficient.

To get the best, the theory ran, you had to balance what the engine could take with your foot. It worked with my old 205 XLD (1.8 IDI rotary pump, small hatchback) amd made it into the most relaxing car I have driven - soft ride, sharp handling, smooth engine and total lack of go - so why bother

[colonelk]

peak torque at 1800rpm? Mines at 2400! its only getting on fully boost at 2200 Price I pay for having an old diesel I guess! Plus 60mph in 5th is at peak torque. Think Im going to have to give P&G another look.....

[slowmover]

The theory at the time was that if you floored it you just pumped loads of extra fuel into the cylinders, a lot of which couldn't be burned efficiently so you actually got no more power but used a load more fuel.

I think that has always been present in IC engines, not to be rude. I simply cannot think of a car I've owned from the 1960's forward that rolling into the throttle gave the best acceleration/fuel use. Throttle lag versus momentum. If it doesn't go towards excess fuel burn it is simply wasted at the tires, spinning or not.

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[Arragonis]

Originally Posted by colonelk

peak torque at 1800rpm? Mines at 2400! its only getting on fully boost at 2200 Price I pay for having an old diesel I guess! Plus 60mph in 5th is at peak torque. Think Im going to have to give P&G another look.....

May be worth trying a tank or so. And in your favour that Isuzu lump will go to Mars and back.

[Arragonis]

Originally Posted by slowmover

I think that has always been present in IC engines, not to be rude. I simply cannot think of a car I've owned from the 1960's forward that rolling into the throttle gave the best acceleration/fuel use. Throttle lag versus momentum. If it doesn't go towards excess fuel burn it is simply wasted at the tires, spinning or not.

I agree you can waste a lot of energy pushing harder without gaining in an IC engine. I think the idea was specifically associated with Diesels as they are fuel controlled - more pedal, more fuel. A petrol unit the fuel delivered depends on airflow, throttle position, temp, boost (if you have a turbo) etc. If you floor it you just open the throttle wide. In a Diesel there isn't one, you just pump in more fuel.

[colonelk]

Originally Posted by Arragonis

May be worth trying a tank or so. And in your favour that Isuzu lump will go to Mars and back.

Yeah it may, shame the car around it is dissolving!

[Small4Seater]

I wouldn't think pulse&glide is that good for a diesel since a diesel usually becomes extremely efficient under constant RPM (and pressure). I have achieved my best MPG by staying in the "sweet spot" in 6th gear.

If I should pulse & glide my little 1.4 (which has push-button ignition, so it takes an additional 3 seconds to turn off at speed), then what would you guys recommend?

I can do some experiments where I simply press the clutch to "glide" and tell you how it goes.

[euromodder]

Originally Posted by Small4Seater

I wouldn't think pulse&glide is that good for a diesel since a diesel usually becomes extremely efficient under constant RPM (and pressure).

I haven't seen any positive results from it either, I'm afraid.
The ScanGauge showed a marvelous improvement, but filling up didn't confirm that.
So I no longer use P&G on long stretches of road.

I do however try to coast as often as possible - i.e. getting up to or keeping sufficient speed so I can coast to certain points where speed needs to be reduced anyway like turns, speedbumps, PSL reductions,... at an appropriate speed.

I can do some experiments where I simply press the clutch to "glide" and tell you how it goes.

I'd put it in neutral and release the clutch again.
To me it's far more relaxed than keeping the clutch-pedal pushed in.

[Arragonis]

+1 the SG2 shows a big improvement - plenty of 55-60mpg average trips but only around 50 when I come to fill up. As I only use one tank a month it takes ages to see the effect.