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GasSavers_maximilian 08-08-2009 05:23 PM

P&G acceleration rate and top speed advice
I tried pulse and glide tonight and it seemed to work (how much is hard to tell because of all the hills). I searched the P&G threads, but had a hard time finding specifics. I was using a top speed of 60 and a minimum of 25 (I was alone on the road as I frequently am). I'm not sure how fast I should accelerate or whether my top speed is at all optimal. Any tips? Thanks.

R.I.D.E. 08-08-2009 07:16 PM

gradual loss of speed uphill in highest gear possible with no more than 3/4 accelerator pedal. Gain the speed downhill.


GasSavers_maximilian 08-08-2009 07:44 PM

Thanks for the info. Just to clarify, what's a good minimum throttle? I've been doing it a lot lower than 3/4 thus far, leading to long pulses which I suspect isn't that great (although it makes for few pulse/glide cycles, which is very convenient). I presume your throttle advice holds for accelerating again after a glide during level travel as well? I'm already pretty comfortable with hills, having had lots of practice, but there are some fairly long mostly level stretches on my way into town. Any ideas on the maximum top speed that's useful on a level? I chose 60 just because it's a 50 mph zone and there are cops there from time to time. From what I can gather from the P&G threads, the speed to coast down to is limited by what you can do in top gear (hence 25 mph). I've been considering how to do a systematic test to find the best settings, but unless I can nail down the approximate max speed or the throttle setting, it'd be an awful lot of combinations.

FrugalFloyd 08-08-2009 09:56 PM

I'd suggest experimenting with 70, 75, 80, and 85 LOD using your Scangauge. Your Accent will probably like 75 or 80 LOD best, like my Scion xB. My higher powered Nissan Sentra SE-R likes 90 LOD better.

I limit my pulsing to a range I can accomplish in one gear, so that's 35-60 mph in 5th gear my Scion on highways, and 35-65 mph in 6th with my Nissan. In practice, California requires at least 45 mph on highways, and traffic usually forces me to use 50-60 mph with the Scion, and 50-65 mph with my Nissan. That's good for about 49 mpg with the Scion and 43 mpg with the Nissan. My mileage goes way up into the 60 mpg range using 4th gear pulsing from 25-40 mph with both cars.

GasSavers_maximilian 08-08-2009 11:31 PM

So fairly high top speed combined with fairly high throttle. Gotcha. I've come up with some testing procedures (instead of sleeping...) to get around the limited length of my test track in case I ever want to systematically try things. I can test the glide part separately, since no matter which throttle I used to get to the top speed it should be the same. Just need avg mpg and miles for the glide (and the pulse) so I can combine them later. The need for multiple data points in both directions (since it's not perfectly level) means I can't test too many throttle positions for each top speed during the pulse, so I'd probably just do three at first (low, medium, high). This assumes that the curves are fairly smooth, which may not be the case, so as a safety check I should do a lot of throttle data points for the most promising top speed to check for local extrema. Since I should really be spending all the times with good weather working on my house, it's unclear when I'd be able to test things out, but it does seem mostly feasible. High top speeds combined with low throttle may still be a problem for my testing length, and that'd be my preferred best case as it requires the least clutch / shifting work.

GasSavers_maximilian 08-09-2009 12:41 AM

I've been thinking about this the wrong way round; rather than trying various throttles for a given top speed, I should be trying various top speeds for a given throttle. Since you pass lower top speeds on the way to higher ones, a single run at a given throttle can hit a bunch of data points at the same time. A lot of data to collect in a short time (and by myself), but my camera can take a movie of my ScanGauge's screen to get around this. Things just got a lot more feasible.

How much extra clutch wear is P&G going to add anyway? Is it even worth it?

GasSavers_maximilian 08-09-2009 01:14 AM

Here's an odd idea: what if you alternated between pulsing and using the best steady state throttle? I can see why pulse and DFCO wouldn't make much sense, but if you reduce your throttle to the best steady state position, the momentum you built up during the pulse would still be contributing and the engine's still being used (albeit at a lower level) to justify the mechanical losses. Since the limit of pulse is ever increasing aerodynamic and road loads (and speed limits), taking a time out for those forces to back off again makes intuitive sense and I don't see why a throttle level that's pretty good at moderate speeds would be necessarily terrible at higher ones (although there is higher drag, it'd fall off pretty quick as the speed dropped). I'd think the speed range would be less than for P&G, but since it'd require no clutch work or shifting in a manual that would be practical. Not as good as P&G, but a lot less work and wear and tear. Any reason this is obviously stupid? A lot of variables to tweak to test this for viability, so many combinations. Come to think of it, steady state may not be the best choice necessarily for the lower power level, so that'd mean four variables: low speed, high speed, low throttle, high throttle. Can take a reasonable guess at a couple of those at least. Let's see...for an initial test maybe try a range of 40 to 55 mph and 75% load for the high throttle. Low throttle I could try at the steady state one, but I have a sneaking suspicion that somewhat lower would make more sense so that the speed and drag dropped off more quickly. Then again, my best steady state speed in high gear is 35 mph, so that's a pretty low throttle setting already.

theholycow 08-09-2009 06:13 AM


Originally Posted by maximilian (Post 139269)
How much extra clutch wear is P&G going to add anyway? Is it even worth it?

None if you rev-match, which you should do. Also, no synchro wear if you double-clutch, which you're halfway to doing when you P&G anyway.

My P&G procedure:
1. Pulse - WOT to the maximum speed I'm willing to go on that road.
2. Neutral:
  • Clutch pedal down, shift to neutral, clutch pedal up.
  • Or, just pull it out of gear; this is fine if you get the timing right. You know you got it right when it feels just like it does when you do use the clutch.
  • Or, in an automatic, just shift to N.
3. Glide down to the minimum speed I'm willing to go on that road.
4. Re-engaging the gear:
  • Manual - Rev-match, clutch pedal down, shift, maybe a supplemental blip if my RPM fell since the rev-match, clutch pedal up & gas pedal down.
  • Automatic - Rev-match, shift to D, and hold RPM if necessary until gear engages.
5. Rinse & repeat.

I don't find huge chunks of P&G (like your 60->25->60) to be worth my effort. I rarely do chunks larger than 20mph.

Until recently, I didn't P&G on the highway. When I first got my car I had a hard time rev-matching 3000RPM (thanks to the bottom-hinged gas pedal, DBW throttle, and my experience being all with American V8 cable throttles and traditional pedals), so I originally gave up on highway P&G. Recently, I remembered that I wasn't doing it, and now I'm pretty good at the VW's unpredictable DBW, so I tried again. It's been worth a large increase. Take a look at Effram's gaslog, the last few tanks have been my best ever.

Anyway, for my new highway P&G, I've been doing 70->60->70 and it's been extremely effective. Sometimes I get as high as 75 or as low as 55 (or occasionally more or less than that, even), but just that 10mph chunk is enough.

The point of P&G is to produce work as efficiently as possible and then disconnect the engine from the road so it's not wasting energy on extra rotations, extra friction and reciprocation, etc. You want to operate in the best range shown on a BSFC map of your engine, and probably near WOT. It works just as well for 10mph chunks as 30mph chunks, you just shift more often with smaller chunks.

GasSavers_maximilian 08-09-2009 06:26 AM

I'd rather do it fewer times because I'm lazy. WOT will mean shorter pulses so I'll have to play around with things and find some combination I'm actually willing to do. I had never heard of "rev-matching" before, but it certainly makes sense. The math suggests about 1,200 RPM for 25 mph in fifth gear.

Realized the same testing techniques for the two position throttle system as for pulse and glide will allow me to try it out on my test strip if I ever want to gauge its performance systematically. Not needing to shift would make me more likely to do it.

GasSavers_maximilian 08-09-2009 06:57 AM

Something that's bothering me; how is all this accelerating near WOT talk reconciled with other advice I've seen that suggests accelerating slowly? I never accelerate fast under any circumstances other than coasting right now. Have I been mistaken in my interpretation of the advice?


45. Be a less aggressive driver
One of the very best ways to save gas is to drive less aggressively. Did you know that aggressive driving (rapid acceleration and braking) significantly lowers gas mileage by as much as 33% on the freeway and 5% in town or the city.

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