Pulse & Glide or In 5th Gear

[oldtamiyaphile]

Originally Posted by mikeyjd

I'm always in 5th by 50km/h (30mph), you must have some really tall gears.

I have two six speeds, one of which is on 2" taller tyres

If we're talking P&G, I generally use a gear lower than I'd cruise at. Sure you can lug the engine at 50 in 5th, but you can't really P&G from that RPM, as any throttle input will shoot load to 100%.

My old MB100 was geared such that 5th at 50 was entirely usable though

I'd guess that in general Euros are geared a bit higher than US/ Japanese cars.

[digital rules]

Originally Posted by mikeyjd

I'm always in 5th by 50km/h (30mph)

Me too, sometimes go down to 25 in stop & crawl traffic with no problem.

[oldtamiyaphile]

I did some coast down testing today, in gear vs neutral. Neutral coast averaged 13 seconds, coasting in 5th (not 6th) predicably reduced my coasts, but only to 10 seconds. Average coast in neutral fuel use is 3.6l/100km (vs 0).

Punching the numbers into the coast down spreadsheet suggest my T5 has a CRR of 0.016, and in 5th gear CRR only rises to 0.020.

Anyway, P&G in gear gives me 6.0l/100km (42MPG US) averaging 90km/h, which is not bad for a 2 ton van.

[oldtamiyaphile]

To answer the original question, it really depends on your specific car.

I've got a collection of quite different cars and they all require a different techinque.

The Jeep won't P&G because it doesn't glide at all. It won't DFCO either because the RPMs in normal use never reach 2000rpm required for DFCO, and if they do, engine braking soon has you back in the idle fuel map.

The Fiat is petrol, turbo and has no throttle plate, it won't P&G either as acceleration burns a lot of fuel, the CD is poor and it's very light (900kg).

It wasn't until I got the MB100 that I finally was able to give P&G (Petrol with throttle plate) neutral or EOC only, but gave great results.

The latest T5 is a P&G in gear champ

In summary it seems for heavy but aerodynamic vehicles P&G is the answer, but for light weight cars or rolling sheds DWL is the answer.

[Fat Charlie]

In my lightweight rolling shed, I usually can't afford even the little bit of braking that the 1.5 gives.

[euromodder]

Originally Posted by oldtamiyaphile

Since your car is a diesel with little engine braking, try pulse and glide IN GEAR.

What makes you think diesels offer little engine braking ?

Quite on the contrary.

[oldtamiyaphile]

Originally Posted by euromodder

What makes you think diesels offer little engine braking ?

Quite on the contrary.

Driving one

Originally Posted by oldtamiyaphile

I did some coast down testing today, in gear vs neutral. Neutral coast averaged 13 seconds, coasting in 5th (not 6th) predicably reduced my coasts, but only to 10 seconds.

Punching the numbers into the coast down spreadsheet suggest my T5 has a CRR of 0.016, and in 5th gear CRR only rises to 0.020.

[user removed]

I pulse and glide everywhere at any speed, in traffic heavy enough to allow a car to pass over the same point every 2 seconds 24-7. 43,200 cars over the same point for a whole day, but I avoid those spots like the plague.

I coast in neutral with the engine on. Not interested in potential damage to the powershift (automated manual) transmission in the fiesta. In fact that transmission is NOT in neutral as I can feel it downshifting as my speed drops below the point where re-engagement would be below 1500 RPM.

I coast in my neighborhood
I coast when the engine is cold
I coast in heavy traffic whether it is going 65 MPH or 15 MPH
Most people around me are so oblivious they do not realize what I'm doing
They do get aggravated when I start slowing down too early for the red light ahead
That's because they are too stupid to understand their own wasteful habits
Divide my speed by 17 then mulitply it by 100 and you have the coasting MPG, which means even on the Interstate with traffic crawling at 17 MPH average speed I can still get close to 100 MPG.

The only thing I am NOT willing to sacrifice is my average speed which hangs around 38-40 MPH consistently. I love saving fuel, but not wasting time and being exposed to increased danger by being among the morons any longer than I legally have to be.

regards
Mech

[TheManVan]

Originally Posted by Old Mechanic

I pulse and glide everywhere at any speed, in traffic heavy enough to allow a car to pass over the same point every 2 seconds 24-7. 43,200 cars over the same point for a whole day, but I avoid those spots like the plague.

I coast in neutral with the engine on. Not interested in potential damage to the powershift (automated manual) transmission in the fiesta. In fact that transmission is NOT in neutral as I can feel it downshifting as my speed drops below the point where re-engagement would be below 1500 RPM.

I coast in my neighborhood
I coast when the engine is cold
I coast in heavy traffic whether it is going 65 MPH or 15 MPH
Most people around me are so oblivious they do not realize what I'm doing
They do get aggravated when I start slowing down too early for the red light ahead
That's because they are too stupid to understand their own wasteful habits
Divide my speed by 17 then mulitply it by 100 and you have the coasting MPG, which means even on the Interstate with traffic crawling at 17 MPH average speed I can still get close to 100 MPG.

The only thing I am NOT willing to sacrifice is my average speed which hangs around 38-40 MPH consistently. I love saving fuel, but not wasting time and being exposed to increased danger by being among the morons any longer than I legally have to be.

regards
Mech

Great reply!

[Fat Charlie]

Originally Posted by euromodder

What makes you think diesels offer little engine braking ?

Quite on the contrary.

Because they had to invent exhaust braking.