How to accelerate in P&G mode? - Page 3 - Fuelly Forums

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Old 06-06-2008, 07:43 AM   #21
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Quote:
Originally Posted by sonyhome View Post
P&G and acceleration.

So if I understand right, experience shows it's most efficient to use the following two modes?
Different people have different experience which leads them to different style (exacerbated by different vehicles). You may have to try a couple tanks one way, a couple the other way, until you choose between any two strategies.

Quote:
A P&G mode: Shift from N into 4th or 5th gear and floor the accelerator with a led foot (or close to that at 80%). That uses WOT with low engine RPMs to accelerate the car.
This is pretty universal. If your car is equipped with a wideband O2 sensor then it probably does not go into open loop mode at WOT, so you can completely floor it. I found out that that's the case in my VW.

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B Red light mode: Accelerating from a stop, use light acceleration (feather foot on pedal), and shift early (say around 2000rpm) until you reach coasting speed.

C alternative to B?: For starting from a stop light, we could also do this: 1st, 2nd with light acceleration and a 2000RPM shift. Then skip 3rd, and go directly to 4th gear (or 5th?), and use a hard acceleration but with low RPMs. Is that what you guys are doing?

I suspect the trick is we need the RPMs for 4th gear to be at least the minimum bearable for the engine, so for starters, the RPMs must be at least 1200 when getting into 4th gear.
I try to use WOT as much as possible, but my car has a lot of low-end torque and it can be tough to moderate my acceleration at WOT. When I do, I shift at 1200 or 1400 RPM, entering the next gear at about 1000rpm. My pattern is as follows:
1st: A light, quick application of gas gets the car rolling enough for 2nd.
2nd: A quick stab gets the torque-strong car fast enough for 3rd or 4th, which are uselessly close in my car.
Depending on my current pattern, I may skip 3rd.
3rd, if I use it: A quick stab and I go from 15 to 20mph, and am ready for 4th.
4th: Now I get a chance to drop it to the floor for a couple seconds, at which point I'm going 25 or 30mph and am ready for 5th.
5th: On the floor until I reach the top of my pulse, then I begin P&G cycling.

Quote:
Automatic: For A/T cars the above seems hard to achieve. as a kickdown will downshift, and a semi hard acceleration will lazilly shift up.
So that should allow you to do (A) and (B), but harder to do (C), unless you have a good pedal feel and can hear when you're in top gear.
My GMC is nice about this, it shifts pretty decently for FE. I can briskly accelerate using a lot of the gas pedal and it shifts firmly at ~2500 rpm. It's nowhere near where I'd shift if I had control of shift points, and I hope soon to get a programmer that allows me to change shift points and such.

Other vehicles may have manumatic-style control, either tiptronic or paddle shifters or etc, and it may be feasible to use a lot of gas pedal and shift low.

Quote:
The difference between (A) and (B) mode in terms of the driver is that in P&G, he would depress the pedal more than when he accelerates from a red light...

Did I get it right?
Yup.
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Old 06-06-2008, 07:47 AM   #22
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Quote:
Originally Posted by 1993CivicVX View Post
But there's no power at low RPMS!
This came up in another thread a few weeks ago. My VX pulls smoothly from 1000 rpm. Or even a bit less. Even in top gear, and even going up a moderate grade, and/or with one or more passengers. I think other VX owners have reported a similar experience. I think there might be something about your engine that is not providing proper power at low rpm. I realize you're still getting good results, but I think maybe you could do even better.

I think I suggested you check the timing. I don't recall if you mentioned doing that.
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Old 06-06-2008, 07:49 AM   #23
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Quote:
Originally Posted by 1993CivicVX View Post
Hypothesis: slow acceleration is always best (except in traffic light matching in Gary's case).

So I'm going back to old conventional wisdom that accelerating slowly is always best for the simple following reasoning: do you accelerate hard to get up to cruising speed when you don't want to P&G? Why, then, should accelerating hard for the purpose to glide afterward be any different?
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Originally Posted by 1993CivicVX View Post
But there's no power at low RPMS! (rest of quote finished later in this message)
Quote:
Originally Posted by PaleMelanesian View Post
I'm not sure the exact dynamics of WHY slow acceleration works better from a stop, while hard acceleration works for P&G. But it does. For P&G, high throttle is unquestionably the best.
You are both treating "throttle" and "acceleration" as synonyms. They are not. Slow acceleration and high throttle combined should provide the best results in most vehicles. Possible points of failure include cars equipped with lean burn (which may be able to accelerate more efficiently with light throttle) and cars that go into open loop at WOT (which is easy to remedy, still use high throttle but not quite WOT).

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Originally Posted by 1993CivicVX View Post
But who am I to argue with a gas getter guru? But I am finding that I'm using less gas with light acceleration and slightly higher RPMs than with full throttle low as possible RPMs. We both have lean burn engines, too, so what's true for you should be true for me, right?
When it's all said and done, you can't argue with results.
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Old 06-06-2008, 08:17 AM   #24
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You're right, I did word that confusingly. Using low rpm in all cases,

Heavy throttle, which still only gives moderate acceleration, is less efficient than light throttle, which gives "slightly less than moderate" acceleration.

This is comparing 80% throttle or so (no enrichment yet) vs. very light - just enough to be gaining speed.
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Old 06-06-2008, 09:48 AM   #25
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most of my driving is short trips so instead of giving the motor a chance to warm up I EOC even if it's only for 5 seconds so it's not idling at 1500RPM. As a result, my battery is often too low to start the engine using the ignition, and on more than one occasion of late I've had to push it when I waited too long to bump start it and failed! The starter doesn't have enough juice to start the car, but enough to bump start. Good times, good times. Slightly embarrassing to have to push the car in the middle of town and then jump in and bump start it. My friend's think it is absurd/funny.
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Old 06-06-2008, 09:50 AM   #26
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Quote:
Originally Posted by monroe74 View Post
This came up in another thread a few weeks ago. My VX pulls smoothly from 1000 rpm. Or even a bit less. Even in top gear, and even going up a moderate grade, and/or with one or more passengers. I think other VX owners have reported a similar experience. I think there might be something about your engine that is not providing proper power at low rpm. I realize you're still getting good results, but I think maybe you could do even better.

I think I suggested you check the timing. I don't recall if you mentioned doing that.
Yeah, I remember this. Maybe there is a discrepancy between our definitions of "smooth" but my car will not pull at 1000 rpm in 5th gear smoothly--it will do it--but I wouldn't characterize the mild vibration and unwillingness as smooth. 1250RPM in 5th gear and the car is very happy. I don't think there is anything wrong with the car--just an old engine (200,000+ miles --dunno how many exactly since the odometer only works about 60% of the time)
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Old 06-06-2008, 10:13 AM   #27
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You might want to charge that battery from mains power to avoid having to get out of the car and push it to start. It really is absurd. This is 2008, not 1908. Plus, keeping it dead all the time will destroy it quickly so it will never hold a charge.
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Old 06-06-2008, 11:16 AM   #28
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how do I charge it from mains power? I'm doing a highway trip tomorrow where I will not do too much EOC. That should charge it up good, right?

I'd like to hook up some solar panels to the battery, but too expensive.
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Old 06-06-2008, 11:28 AM   #29
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how do I charge it from mains power?
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Old 06-06-2008, 11:32 AM   #30
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Here is my route one way.

4.5 miles, 55 MPH, 1 traffic light at the end, 4 lane non divided highway with Interstate on one side and railroad tracks on the other, perfect for hypermiling because everyone is on the parallel interstate. Plenty of room and time to DFCO and catch the light green every time. 4 different downhill slopes for coasting about 30% of the total distance. I usually stay about 50 MPH on this stretch.

3.5 miles, 45 MPH, 1 traffic light at the end, same 4 lane non divided highway, city park on left, Interstate on right, light traffic. More nice downslopes to help maintain speed when coasting.

3 miles, 45 MPH, 9 traffic lights mostly well timed but some will always catch you due to triggering of light by traffic entering road. Some construction, normally has a left turn lane, but not in construction area. Speed limit drops to 35 in construction part. Still 4 lane, but traffic can get heavy here especially if Interstate is not moving. Left turn at the end is most difficult to time properly, most idling at this point. Lots of DFCO here. Rabbit morons race to red light and mess up your timing.

1 mile, 4 traffic lights, 4 lane divided, very hard to time lights due to light timing controlled by entering traffic. Fortunately lights change fairly quickly.
Lots of DFCO on this short section. This is where the rabbit morons blast by you and crap up your light timing.

3 miles, 1 traffic light at end but right turn on red so waiting time is usually short, two lanes 45 MPH. Lots of elevation changes where coasting speed can remain alomost the same as average speed. Usually not much traffic. Lots of chances to coast down from 45-50 to 30-35, when no one is behind you. Pulse on inclines and glide on declines is the norm here, and that is typical of my strategy with the very gradual elevation changes that are typical on this whole route.

1 mile, 45 MPH, 2 traffic lights, 4 lane divided, traffic is usually fairly heavy. Hard to catch those 2 lights green, sometimes the traffic is 30 or more cars at the light when it changes and there is no way you can coast up on them and catch the light green. Nice chance to coast downhill then back uphill in this stretch.

6/10 mile, 1 traffic light at the end, exit ramp to overpass, good spot to use your speed to coast up the ramp to lower speed limit. DFCO to light at bottom of downslope to left turn at light. In most cases I can catch it green and turn immediately, but the light is switched by someone in the left turn lane, so on occasion you have some idling.

1.4 miles, 40 mph, two lane residential areas and two schools. Opportunities to coast on downhill areas and back uphill at almost constant speed due to elevation changes. Pulse begins halfway up the upslope to speed limit. Opportunities to coast to much lower speeds when no one is behind me.
Left turn at the end of thsi stretch with no traffic light. I make the turn in 3rd gear.

7/10 mile, 40 MPH, two lane, starts downhill so I can coast halfway then pulse and coast one more time on this stretch. Stop sign at the end for DFCO opportunity.

1/10 mile, 35MPH, to vehicle actuated left turn, always a crap shoot on this one. Sometimes I am the trigger, sometimes someone else catches it and I have to race to get through, sometimes I just have to trip it and wait 25 seconds. Ideally I can coast through when I have another vehicle to trip the light at the perfect time.

6/10 mile, 55 MPH, 2 lane, good chance to coast at the end, left turn trip actuated light, another crap shoot as far as timing, worst case is about 25 seconds wait.

19.4 miles 22 traffic lights, usually takes me about 40 minutes if I use this back road route.

In this area the notorious traffic jams are areas that can have 100,000 vehicles cross a single point in one day. Thats better than one vehicle per second (86,400 seconds per day). That means on a two lane choke point you have 50,000 cars daily per lane, every 86,400 seconds, or less than two seconds apart for 24 hours. Of course its always worse because there are times when it is really bad, and times when its not bad at all. 8 mile traffic backups happen almost daily in this area, called the Hampton Roads Bridge Tunnel.

These areas and traffic nightmares are usually not an issue for me. I stay off the beaten path and use roads I have used for 42 years. The same turn I now coast through at 35 MPH (the speed limit), I used to go through at 70 in my 59 Vette. It would do 70 on the average Interstate cloverleaf. I averaged 20-22 MPG in that car in 1973 the year the speed limits were reduced to 55 MPH nationwide. The Vette came with a 4.11 rear end which I ripped apart in two weeks. Changed it to a .308 ($25 part) and it tached 2100 at 62 MPH.

Current average 59.18 MPG

regards
gary
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