Floor the throttle to save fuel - Petrol only !

Bigus

There was an interesting article in Autocar about 8 months ago which tested a technique which seemed to go against all logic.

Basically it involved Flooring the accelerator and then gliding,(going on the overrun) for Petrol engines.

The theory is that modern fuel injected engines will only deliver the correct amount if fuel for a given engine speed, regardless of throttle position.

Also Modern fuel injection delivers NO fuel on the overrun but uses vehicle momentum to keep the engine turning.(this is why its not a good idea to freewheel because fuel is used to keep the engine ticking over)

By flooring the accelerator the throttle is wide open reducing pumping losses leading to much greater engine efficiency (up to 30% of fuel is used to overcome pumping losses)

One of the reasons Petrol engines are less efficient than diesels is because Diesels aren't throttled, and don't suffer from the same pumping losses.

Anyway Autocar tried this unusual technique on 4 or five different petrol cars and made reductions in fuel consumption of between 15 to 25 % depending on car tested, but with the same driver.

So the technique involves Flooring the throttle and then lifting off, in practice you can see how indeed this can save fuel because the amount of TIME the accelerator is pressed becomes much less.

In practice for most people this may only mean labouring up hills in fifth gear with foot to the floor as against going up the same hill in third gear on a partial throttle.

I tried this in a 03 Punto (not Mine)last sunday and averaged 61.4 Mpg on a 60 mile round trip (according to trip computer)

The Americans refer to to this as pulse and glide

Some examples http://www.metrompg.com/posts/pulse-and-glide.htm

http://www.youtube.com/watch?v=_f9hKAktvtk

Midnight_EG

Now let's wait for everybody to pull wheelspins at the lights when they take off :rolleyes:

cabrwab

Quick question would this not cause motion/sea sickness type motion?!

Antrim_Man

I would not want to be in a car with someone driving in that manner

line6

would be dodgy in a car with power assisted brakes

ShadowHearth

So basicly foot down 100%? Then clutch, gear out, and glide on neutral revs?

I doubt it will end up well in skyline...

dylbert

ShadowHearth wrote: »

So basicly foot down 100%? Then clutch, gear out, and glide on neutral revs?

I doubt it will end up well in skyline...

I think your ment to stay in gear

Mr Benevolent

What a crock of shit. All pulse & glide does is cause road rage and accidents.

650Ginge

Confab wrote: »

What a crock of shit. All pulse & glide does is cause road rage and accidents.

Most people pulse and glide without trying or noticing, hardly anyone remains at exactly the same speed all the time. Yes using cruise I know will maintain the same speed but it will pulse and glide too, say over crests and slight inclines or whatever.

Pulse and glide can work with very little difference between the target speeds, only a 5kph difference will do it.

But it is way too much effort, I tried it and it requires maximum concentration all the time. I just get to whatever speed I want under or at the speed limit and hit the cruise and relax a bit.

Reducing speed is the best way to increase mpg, but ever car is different and the ideal speed for one is not the same as the other.

dr.fuzzenstein

line6 wrote: »

would be dodgy in a car with power assisted brakes

Haven't they all been power assisted since the early 70's?
Unless you're passenger in a car in a classic car rally.
I'd hate to be stuck behind someone doing that, happened once from Ennis to Gort, this car was doing 60-80-60-80-60-80-60-80 (km/h) all the way, I couldn't get past because of long line of cars all forced to do the same.
And did they pull over?
Did they, fcuk!
At last in Gort they did, which was followed by a barrage of horns and abuse from passing and very irate motorists, not least of which, me.
I don't think they got it, by the time you pull sh*t like that you must be SO thick and ignorant, you'll make a person in a coma look alert and responsive.
As for being a passenger in a car like that, I hope there's a good supply of sick bags in the glove box!:D

Bigus

ShadowHearth wrote: »

So basicly foot down 100%? Then clutch, gear out, and glide on neutral revs?

I doubt it will end up well in skyline...

No ; reread first post

Also this is foot to the floor at LOW revs, not flat out through the gears on full boost.

BrianD3

I've often wondered why I seem to get very good economy on regional roads with lots of bends and hills. Obviously the 80 km/h limit helps but maybe I've also been doing a form of pulse and glide.

line6

line6 wrote: »

would be dodgy in a car with power assisted brakes

no it wouldn't, wouldn't effect the brakes at all, engine is still running. The reference to diesel engine not being throttled is neither hear nor there really. It's the air that isn't throttled. I wouldn't mind reading the detail first hand though

Bigus

RoverJames wrote: »

The reference to diesel engine not being throttled is neither hear nor there really. It's the air that isn't throttled. I wouldn't mind reading the detail first hand though

Yes it is relevant here .

A diesel engine suffers less pumping losses because it doesn't have to pull/suck air with difficulty by a throttle restrictor/restriction.

This is technically the whole point of foot to the floor in a petrol. A wide open throttle in a petrol engine makes it more efficient.

This is why Fiat have introduced Twin Air and Mult-iair(Alfa Romeo) technology engines with no throttle to improve the efficiency in Petrol engines by up to 20 to 30%

On the pulse and glide annoying other drivers , it is possible to do this or a version of this without affecting them.

Matt Simis

Also hard to do in an auto! I might try it though (in Tip mode).

Bigus

Matt Simis wrote: »

Also hard to do in an auto! I might try it though (in Tip mode).

Yes Kickdown would void any gains but an auto will glide longer.

I passed you in that red Punto the day i was trying it on the lucan Bypass last Sunday. I recognised the Winter Tyres !

Bigus

Matt Simis wrote: »

Also hard to do in an auto! I might try it though (in Tip mode).

Also might only work with later injection systems

Bigus

Bigus wrote: »

A diesel engine suffers less pumping losses because it doesn't have to pull/suck air with difficulty by a throttle restrictor/restriction.

This is technically the whole point of foot to the floor in a petrol. A wide open throttle in a petrol engine makes it more efficient.

Can you explain this a bit more please?
I don't see how pumping losses use any more fuel, especially on a petrol as the pumps are electric and not belt driven like on diesels.

Mr Benevolent

RoverJames wrote: »

Can you explain this a bit more please?
I don't see how pumping losses use any more fuel, especially on a petrol as the pumps are electric and not belt driven like on diesels.

Pumping loss is the power required to push the exhaust gases out of the cylinder and suck in fresh fuel and/or air. Nothing to do with actual pumps

Matt Simis

Bigus wrote: »

I passed you in that red Punto the day i was trying it on the lucan Bypass last Sunday. I recognised the Winter Tyres !

Lies, a Punto could never pass an S8! :P
Those winters really need to come off for a 18" Summer set (and a repaint, damn snow is harsh stuff).