How to accelerate in P&G mode?

[sonyhome]

P&G and acceleration.

So if I understand right, experience shows it's most efficient to use the following two modes?

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.

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.


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.

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?

[theholycow]

Originally Posted by sonyhome

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.

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.

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.

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.

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.

[sonyhome]

Originally Posted by theholycow

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.

Holycow, that's confirming my intuition is wrong and I need to review my red lights starts. Hondas don't really have much low end torque, they tend to have a longer power band and high-RPM limits with VTEC.

One more reason to hook up a PC to the car, to see where my gas is spent on my commute. i do get a lot of gliding, and I try to sync lights as much as possible.

I'll try to P&G in 5th gear (but I don't like -hum- slow accelerations in traffic).

BTW, I've found yet another way to hypermile: The AAA credit card gives 5% cash back on gas :-P

I not RPMs, flooring the accelerator, the injector duty cycle is close to 100%. So there's a max amount of gas in the piston. Is the explosion complete (gas fully used)? Is there always enough oxygen for the amount of gas pumped in the piston?

[R.I.D.E.]

Look at a Brake Specific Fuel Consumption Map.

There is an area on the map that represents the most horsepower for the least fuel. I like to call it the "sweet spot".

The most basic and essential component of effective P&G is to understand that you try to stay in the "sweet spot".

The Sweet Spot is easy to determine even without special equipment.

Put your car in a gear that is higher than you would normally use. The Sweet Spot is the point where when you apply increasing amounts of throttle, you get almost no difference in acceleration.

It takes a very long time for my VX to accelerate from 1200 RPM to 2000 RPM in 5th gear, compared to using second or third gear, or even fourth gear.

Given the option by the traffic around you, use the highest gear at the lowest RPM for the pulse.

In some cases I actually have to downshift in order to accelerate more rapidly. After driving for 42 years, my shifting is second nature, including any rev matching. I don't look at any instruments, it's pretty much instinctive.

I have to stay within a minimum and maximum range of average speed to keep in time with traffic lights. When it works I can go through 26 lights without idling for 1 minute total time in a 20 mile drive.

This requires me to accelerate faster than I would if I had no lights or traffic to deal with. MY success at "adaptive P&G" is reflected in my mileage.

If I was on Route 17 north of Gloucester VA, where the road is 2 lanes, divided, with a 55 MPH speed limit and virtually no traffic, I could probably get close to 70 MPG, without EOC.

I read here that turning off the engine on a VX, causes the lean burn system to not work for 30 seconds after a restart. I may test this one day when I have time, and I am working on a very simple system for topping off my fuel tank in increments of less than a gallon, so I can make precise comparisons under identical situations without haveing to drive 250+ miles between fillups. That range of distance for me only uses about 40% of my tank capacity.

regards
gary

[1993CivicVX]

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?

[theholycow]

Originally Posted by 1993CivicVX

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?

Originally Posted by 1993CivicVX

But there's no power at low RPMS! (rest of quote finished later in this message)

Originally Posted by PaleMelanesian

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).

Originally Posted by 1993CivicVX

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.

[palemelanesian]

Mine's not lean burn. You might actually have better results than I do with light acceleration. One more tool in your toolbox than in mine.

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.

From a stop, for me in my car on my commute, harder acceleration will yield low 60's mpg, while feather-light acceleration will give me upper 60's and sometimes into the 70's.

(RIDE's advice differs from mine in part because he has LOTS of traffic lights to deal with, and I have relatively few. Also, he has lean burn and I don't.)

[palemelanesian]

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.

[1993CivicVX]

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.

[theholycow]

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.