Do you think my p&g hypothesis will hold true?

[320touring]

I'm now getting consistent 40mpg uk tanks out my Saab..

pulse and glide seems to be very effective go this car.currently on the motorway i use the band 65-50mph for p&g.

on my next tank I'm considering using a 60-50mph band

my hypothesis is this..

a-the pulse phase will be shorter

b-the glide phase will be shorter

c-there will be more pulses per trip

d-aero drag will have less impact

e-my overall mpg will increase.

the majority of my runs are on one road,and i know the topography well.

do you think my hypothesis will hold?do you have experience of making similar changes to your p&g?

talk away

[dcb]

speaking of topology, There is some "artistry" to p&g, i.e. knowing when to stretch/cut short a glide (or a pulse) to line your pulses up with the hill climbs and your glides with the downhill coasts. If you lived in a flat area then such a mph only evaluation works pretty well, but if there is genuine topology then you want to incorporate that to some degree as well.

Looking at a topo map, I'd say chances are you got topology in scotland most efficient scenario for large hills you want to cut a near peak bsfc burn on the climb such that you just barely coast over the crest of the hill, then let gravity take you back to speed, then coast partway up the next hill till you slow down to a good bsfc speed and pulse/climb again.

[320touring]

Thanks for the repy DCB..

I'm currently doing 250 miles a week running on the m8 from Glasgow to livingston (about 1/2 way to edinburgh)

So i'm actually in the "green" section of the topography, mainly gentle, long hills that I have, and i've pretty much got it down pat for the hills as is.

Do you reckon the drop to 60 could cause issues in doing 2 pulse/glides to get up a hill?

[Daox]

Your hypothesis' sound right to me.

I usually don't glide up hills very often unless its a fairly gradual hill. The object of P&G is to heavily load the engine. Going up a hill increases load quite a bit. So, normally I just climb it at whatever is needed to maintain speed, or achieve my max pulse speed by the top.

[320touring]

Originally Posted by Daox

Your hypothesis' sound right to me.

I usually don't glide up hills very often unless its a fairly gradual hill. The object of P&G is to heavily load the engine. Going up a hill increases load quite a bit. So, normally I just climb it at whatever is needed to maintain speed, or achieve my max pulse speed by the top.

Thanks for that Daox,

On my commute, a lot of the Hills co-incide with the on ramps for the Motorway..

so by gliding, I can reduce speed enough to allow folks to merge without braking

I do ofeten find myself completing the pulse at the top of a hill.

i've got 1 section on the route home that allows me to coast approx 3 miles by doing 2 short (200m) pulsed- this is a big factor in my MPG figures I think.

Glad you think the hypothesis is good.

Can I expect a sizable gain? e.g. 1 mpg?

[bestclimb]

I have no scientific explanation for my thoughts on your hypothisisisisisis just my swag.

a-the pulse phase will be shorter
Cause your not accelerating as much,
b-the glide phase will be shorter
Yes but by a smaller amount than the pulse.
c-there will be more pulses per trip
a few more
d-aero drag will have less impact
slightly as 60 > 65 (woo now there is some crazy math)
e-my overall mpg will increase.
that is likely.

[skyl4rk]

You should see some gain from slowing down your top speed. You might do better than 1 mpg.

If you can turn off the motor on your long coasts, your FE gains will be very high.

[robchalmers]

I think the theory holds water mate especially point d - due the exponential drag increase with speed. (negating head/tail winds)

looking a the topo-map I'm in a green bowl too!

[320touring]

Originally Posted by skyl4rk

You should see some gain from slowing down your top speed. You might do better than 1 mpg.

If you can turn off the motor on your long coasts, your FE gains will be very high.

Cheers, I dont like EOC on my commute-the traffic is too heavy to try that without a vacuum tank etc.

Robc- cheers chief, we should probably mount an expedition over one of the "orange bits" to have an ecomodder UK meet!

Bestclimb- I know my thoughts seem logical, however, this FWD swedish thing is a confusing car!

[Old Mechanic]

Everything depends on the grade and length of the hills.

On very slight grades you can climb with almost no difference in fuel mileage compared to driving on level ground. The increased load means increased efficiency. It is surprising how little difference a slight grade makes, especially if your car has higher RPM in your highest gear.

If the hills allow you to coast downhill for a considerable distance without a significant loss of speed (like the example of two pulses in 3 miles) that is just about perfect for great mileage.

The peak pulse speed should be as low as traffic will allow without aggravating other drivers, and if you have the opportunity to follow a large truck at a safe distance the improvement could also be significant.

I don't think multiple pulses uphill is the best solution, but that is a very grade specific assumption on my part. Better to climb in highest gear as long as you do not have to use more than about 50% of your throttle position percentage.

If the downhill grade is low enough to have to pulse on the downhill section, I would try to hit my peak speed at the top of the hill, to extend the glide phase downhill to the greatest extent.

Adding energy uphill is most efficient, but also consumes the most fuel based on time alone. Like the roller coaster you want to maximise your tactics to all of the circumstances of your particular trip, while being polite to other drivers and not creating a frustrating obstruction to their efforts.

It sounds like your terrain is just about ideal for maximum mileage. On one trip in my CVT Insight, averaging just undeer 55 MPH, for 650 miles, I managed to get 70.2 MPG US.

My conditions were similar, but during one section of about 70 miles I had to deal with elevations of over 2000 feet.

regards
Mech