Thinking again here similar idea to P&G

[ps2fixer]

Of how I understand P&G, you speed up quick, kill the engine and coast in neutral and repeat the cycle to get your wanted average speed.

My question would be then, If speeding up quickly is more effective than speeding up slowly (max mpg while running) wouldn't speeding up fast to your target speed, and continue at that speed and EOC when you need to slow down/turn? Maybe I'm just not understanding how P&G actually works

Another look at a similar idea in engine design, the hit and miss engine. So my next question would be... what is more efficent, our standard style engine or one converted to be a hit and miss say at 1/4-1/2 load or even idle (engine on coasting?? lol)

Which is more fuel effecient? - SmokStak



Even if the hit and miss design isn't more efficent, a smaller engine typically consumes less power to maintain speed compaired to a larger engine. So I got thinking that it might be possible to drop 2 cylinders from running a an I4 engine once you are up to speed with some sort of similar design as a hit and miss but be user controllable and would have to take into account cutting the fuel injectors off for the 2 cylinders as well as a cam over-ride system to reduce the air pumping losses.

Just a small background on this, my uncle told me of a story of someone he knew years ago that modified a small car that had a I4 engine so that it was a I2 engine (removing the pistons and grinding the cam loabs maybe?). It had hardly any power (story stems from him having to help push it in loose sand). He claimed the driver was getting 60-70mpg and took well over a mile to get up to speed. I would suspect the driver probably drove slower aswell.

Same uncle talked of another guy that put a small 4 cy engine and put it into a full sized van which then became FWD with similar results but more like 30mpg. These numbers are just from memory (and his!) but I suspect they were real world storys, just the numbers could be off a bit.


Anyway, discuss what you think, examples are always interesting.

[GRU]

I never thought about the idea of removing a few pistons, but would work. Not sure how much it would improve fuel economy

[Ladogaboy]

Originally Posted by ps2fixer

My question would be then, If speeding up quickly is more effective than speeding up slowly (max mpg while running) wouldn't speeding up fast to your target speed, and continue at that speed and EOC when you need to slow down/turn? Maybe I'm just not understanding how P&G actually works

I forget who wrote the article, but the gist was that it is actually more fuel efficient to "briskly" get up to your desired speed than it is to slowly accelerate. As I remember, the testers chalked that up to the idea that driving in your highest gear is most efficient; however, after starting to do more research and reading more information on this site, I'm inclined to believe that their findings are partly the result of the increased efficiency at an increased load.

[Daox]

Look up 'brake specific fuel consumption' maps. We have a bunch posted in the wiki link up top the page. It will show you that every engine is most efficient when it is loaded to around 80%. That is where you get your brisk acceleration from. If you had a smaller engine and still loaded it to 80% you'd just have normal acceleration, but that would be "too slow" for the average driver.

Cylinder deactivation is being used by a few OEMs. Everyone seems to do it a little differently. Its not really anything all that new.

[ps2fixer]

Interesting data, I didnt' even see the Wiki Link before >,<.

Anyway I think i'm going to try a few tanks taking off slow like I'm doing now and compare to ~80% load take offs (when I can). Seems to me that I was getting better MPG when I have a week of "omg i'm running late, speed up faster!", of course I was braking as late as possible to save time >,<. It's funny that I drive ~50mph now and try not to exceed 2500rpm (shift points at 2200 when possible or less) .

[roosterk0031]

SGII shows best acceleration load

Basically the harder he accelerated the better MPG in his P&G cycle.

I don't think automatic tranny's will have near the results, I can't load my engine anywhere close to 60% without downshifting & TC unlocking.

[redpoint5]

I have adopted an early shift habit and keep the engine load close to 85% under acceleration. I'm not sure this makes a huge difference, but overall I am getting 2mpgs better than when I first got the car. This is probably mostly due to learning the glide points on hills and memorizing traffic and light patterns though.

[SentraSE-R]

Originally Posted by ps2fixer

Of how I understand P&G, you speed up quick, kill the engine and coast in neutral and repeat the cycle to get your wanted average speed.

My question would be then, If speeding up quickly is more effective than speeding up slowly (max mpg while running) wouldn't speeding up fast to your target speed, and continue at that speed and EOC when you need to slow down/turn? Maybe I'm just not understanding how P&G actually works

The way to turn a 40 mpg highway drive into a 50 mpg highway drive is high speed pulse and glide. Normal driving @ 60 mph = ~1.5 GPH. 60 mph/1.5 gph = 40 mpg.

When you pulse from 50 mph to 60 mph, or 55-65 at moderate acceleration, you guzzle gas at ~3 GPH (60/3 = 20 mpg). When you glide back down from 60-50, or from 65-55, you're in neutral, sipping gas at .14 GPH (60/.14 = ~430 mpg). But you're accelerating only 1/3 of the time, about 8 seconds average on a pulse, and gliding 2/3 of the time, ~16 seconds on the average glide.

Over an hour, P&G has me using 3 GPH for 1/3 hour, or 1 gallon, pulsing. Add .14 GPH for 2/3 hour, or .09 gallon. 60 mph/1.09 gph = 55 mpg.

P&G benefits get much better at slow speeds. P&G in 4th gear, 25-40 mph, engine off, means the engine runs 25% of the time. P&G in 3rd gear, 18-32 mph, I'm only running the engine 15% of the time.