Pulse & glide not always better than steady speed in-gear?

[IamIan]

Speed variation is always an aerodynamic penalty over maintaining the same average speed .. under any and all methods .. any speed .. etc... This is a consequence of the exponentially increasing wind resistance.

P&G works as a net vehicle benefit when some other effect of the P&G overcomes the aerodynamic penalty for speed fluctuations.

One of the big effects that can beat the wind resistance penalty many times in P&G is the net ICE operating efficiency... So look for the BSFC for your ICE and try and line up your P&G with the best net ICE operating efficiency.

As others have said , this is easier to achieve at slower speeds .. because the larger the aerodynamic penalty the harder it is to find some other drive method benefit to overcome them... and wind resistances increase very fast with faster speeds... Wind resistance force increases @ V^2 .. wind resistance power increases @ V^3 ... 10mph to 40 mph is 16x more wind resistance force and 64x more power... but only 4x faster.

[i90east]

Originally Posted by IamIan

One of the big effects that can beat the wind resistance penalty many times in P&G is the net ICE operating efficiency... So look for the BSFC for your ICE and try and line up your P&G with the best net ICE operating efficiency.

Thanks for the info IamIan. It seems like my little hatchback is not very aerodynamic and I can definitely feel the resistance at higher speeds. I seem to do best around 35 MPH with this car but I'll look into engine efficiency.

Originally Posted by dirtydave

How many RPM's in 5th at 55MPH??

RPM at 55 MPH in 5th is around 2,500.

Originally Posted by Fat Charlie

What kind of instrumentation do you have? Instant and trip are the bare minimum, but short trip is where you can compare different conditions and techniques.

I've just been looking at instant MPG and then seeing what the results are when I fuel up. I will try setting short trip MPG on my Ultragauge. Thanks for the tip Charlie!

[mikeyjd]

The best results I've had with various manual transmission vehicles has with pulse and glide from 30-45 EOC back down to 30 repeat. I try to drive as close to this as my situation and time permit.

In my experience, pulsing over 60mph will generally have a negative impact on your economy no matter what else your doing. Since you have an Ultra Gauge you should be using engine load % to help you determine how hard to accelerate for most efficient results. I find 69-71% load yields optimal results in my 3.4L Tacoma while around 85% is better in my Dad's 96 Ford Aspire.

Unless you can find a bsfc chart you will have to determine this through trial and error.

In ideal conditions I can get over 40mpg in my 4x4 v6, but conditions are rarely ideal!

[Focus-Ak]

Originally Posted by mikeyjd

... find 69-71% load yields optimal results in my 3.4L Tacoma while around 85% is better in my Dad's 96 Ford Aspire. ...

I'm interested in how you make the determination of what %-load is optimal. On my UltraGauge the percentages are ephemeral since acceleration periods are usually brief, and are very sensitive to throttle position.

I haven't been able to find a BSFC chart for my engine (2.0 L Duratec in a 2005 Ford Focus), so I have been trying to hit 75%-85% as a generic best guess, and figuring that 65% to 75% is probably good at lower than 1300-1800 RPMs. Guesswork, as I said.

But backing off the pedal just the smallest tad drops me from, say 95% to 60%, so it's quite hard to hit my guesswork sweet spot.

(I also notice that, while accelerating, I need to progressively add bits pedal displacement to keep in my target %-load range.)

Sorry for the digression. My question is in the first sentence.

[j12piprius]

Originally Posted by Focus-Ak

On my UltraGauge the percentages are ephemeral since acceleration periods are usually brief, and are very sensitive to throttle position.

The same for me. I go up to 90% MAP on pulses, about the same as 90% engine load. The results at 80% have not appeared nearly as good, based on trial & error while keeping close watch on the ultragauge trip average mpg.

I also notice that, while accelerating, I need to progressively add bits pedal displacement to keep in my target %-load range.

I saw a report that greater increase in fuel is triggered by quicker change in acceleration, so I've endeavored to sneak up on 90% MAP rather than going there instantly. However, I don't know if this makes any difference.

[awcook]

The more instant you blip your throttle, the more fuel you will use, at least if your car is drive by wire. If I gently squeeze into the throttle, RPMs go up slowly, and I get up to desired gal/hour (3). When I quickly go onto the throttle, for about half of what I do when I slowly squeeze, the RPMs jump up to 2.5-3k and I get about 4 gal/hour for a few seconds, then down to what it is supposed to be, which is about 2 gal/hour.

I haven't found any BSFC charts for my car in particular, but others with the same displacement seem to say that between 3 and 4k RPMs is where I get the most torque per drop of fuel used.

[j12piprius]

Originally Posted by awcook

If I gently squeeze into the throttle, RPMs go up slowly, and I get up to desired gal/hour (3). When I quickly go onto the throttle, for about half of what I do when I slowly squeeze, the RPMs jump up to 2.5-3k and I get about 4 gal/hour for a few seconds, then down to what it is supposed to be, which is about 2 gal/hour.

Perhaps you're simply overshooting the rpm, and then coming back down to a desired peak, which is not the same thing as gradually increasing to that peak.

I'm speaking of either quickly going from 1500 (for example) to 2500 rpm right at 90 MAP, and then gliding, vs slightly more gradually going from 1500 to 2500 rpm, i.e. more gradually up to 90 MAP which still only takes a few seconds, and then gliding. There is only a slight and subtle difference between these, and no overshooting involved either way.

[awcook]

I know what you are saying, johnlvs2run, but I remember reading somewhere that immediate change in engine load shifts the car into a different VTEC mode, thus using more fuel than gradually changing engine load.

I do know what you are saying though, I haven't played around too much with it though, so that may be the case. I'll check in more on it later this week.

[j12piprius]

Originally Posted by awcook

I know what you are saying, johnlvs2run, but I remember reading somewhere that immediate change in engine load shifts the car into a different VTEC mode, thus using more fuel than gradually changing engine load.

Yes, that's what saw as well.

[i90east]

I'm getting much better P&G results now that I'm using lower gears to pulse instead of the overdrive gear. I haven't done a full tank yet but I'm pretty sure I'm getting a 3-5 MPG increase over staying in gear. All of that rapid acceleration can't be good for the tires though and I'd probably drive passengers nuts if I drove this way with them in the car. Haha!

I'm starting to bump start more often as well but I'm wondering, has anyone had problems arise from doing a lot of bump starts?

Thanks again for the advice.