Basic questions for fuel effiency

[Arragonis]

Originally Posted by actwithclarity

I learned myself to drive standard from reading a page on the internet. Basically I can drive around half smoothly but I have no idea:

~ how much gas to apply [just hard enough to not stall .... burning rubber]
~ when to shift [lowest rpm for next gear .... highest rpm for this gear]
~ what gear to shift into [next number gear, skipping one, highest possible, etc]

(to get good fuel efficiency)

Please help me understand these basics. A video would also be helpful if anyone has one.

The "things you can do to improve" lists on here - see the stickys - are a starting point, but there isn't a magic spell technique or mod which works for every car or even the same car in different environments.

You have to get some feedback in the form of instrumentation and work it from there using maybe a quiet road or a non-busy part of your commute and compare the different techniques available.

For myself I prefer the low revs idea and sometimes combine that with gear skipping - 1-3-5 or even 1-2-4-6 (the 1-2 is to get rolling). A merging or slipping clutch is a wearing one though. Also bear in mind I drive a Diesel which has a heavier flywheel and mega torque at low revs and so is much harder to stall and happier on a light accelerator touch as it has no throttle restricting airflow - it is fuel controlled - your car may be different.

Good luck, and post back results for others to share.

[Frank Lee]

Yes, I should point out that not all cars "like" gear skipping. I've tried it on a Metro and there was a little "crunch" (yes, I worked the clutch and rpms correctly) so I don't ever do it on that car. My Tempo doesn't mind at all though.

[justjohn]

The only gear I tend to skip is 4th, and only if I'm already at the speed limit after going through 3rd. My thought is to keep it near as near the ideal spot on the bsfc chart as possible. The more gears you use the closer you can stay to your target rpm.

If someone has a convincing argument in favor of skipping I'd love to hear the reasoning though. (Clutch wear doesn't count - I rev match every shift)

[actwithclarity]

Originally Posted by Bill in Houston

post a video of yourself, and then we will critique you.

I am learning a lot of new things in my job lately. The method for learning is not to pick something up without a clue and try to use it, and then have experienced people explain everything and try to cope with it. The method is to first watch experienced people doing their thing, and then try to mimic what you have observed. Then they give feedback on the tiny things you still need to learn. A picture is worth a thousand words they say so I hope to find a video of someone else driving a standard for good fuel efficiency before I would post my own attempt.

Originally Posted by justjohn

My thought is to keep it near as near the ideal spot on the bsfc chart as possible. The more gears you use the closer you can stay to your target rpm.

I saw the BSFC chart but had trouble trying to interpret it. Where do I want to be on the graph??? The bottom line (lowest fuel efficiency) always correlates with the lowest load, or is it torque? How does the load on my car vary when driving on a level surface? How do you determine what gear to be in by looking at this graph? Any insight would be nice.

[bestclimb]

Correlates with lowest load. The best explanation I have read is that you want the fewest highest load combustion events as possible.

You want to be at the peak, or lowest fuel consumed/horse power.

[actwithclarity]

OK! I think I understand most of it.

I'm looking at this graph for example:


You start at 1000RPM, 0Nm, and your goal is to get to 3000RPM, 55Nm as efficiently as possible, and then stay as near to that as possible. You have 5 jumps during your acceleration to make it there.

What I am not entirely sure about is how engine torque fits in the picture. If you are driving at 1000RPM for example, what determines the amount of torque? Is it constant? Is it determined by the load? What else? Perhaps if someone could explain for me what happens in the first 10 seconds from a dead stop in first gear it would help me understand.

[MetroKindAGuy]

Nice Graph !

I have an observation and a comment, and a question.

some info. I have a 91 metro vert. I converted to 5 spd.( Homemade bed frame for transmission mount. As it wont take the standard mount.)4 dr metro tranny, higher gears than stack convert tranny.

I have recently installed a vacuum gauge, my engine pulls 18psi at idle. 21 is max decellerating. Gauge is cheap and my engine does have new rings. I use the reading for reference only.
So heres the question....
I notice than in 5 th gear that it sweeps faster (down) when I have to gas it, to get up hills and I can only maintain a 9 psi avg (2750RPMS). Compared to in 4 th gear when I'm running say 3250 RPMs, I can maintain a 10/11 reading. While driving between 45-50 mph in both cases.

So, Is it more effecient, to rev higher at higher vacuum reading, or should I shift to 5th and concentrate my efforts to keep the lowest rpm.?

Before I had the gauge, I always upshifted asap.
Now with the gauge, I believe I do better Reving.

anyone have a graph with mph/mpg on the 1.0 metro?

Thanks in advance, and hey anyone thought about a 20 hp Briggs powered metro/drivetrain. Or maybe motorcycle engine powered metro?

[Joenavy85]

Originally Posted by MetroKindAGuy

So, Is it more effecient, to rev higher at higher vacuum reading, or should I shift to 5th and concentrate my efforts to keep the lowest rpm.?

more efficient, less economical.

you'll make more power for a given amount of fuel burned (more efficient)

However...

you don't need that much power to maintain speed (less economical)

once you're in top gear keep RPM's as low as you can and still maintain speed for the optimum MPG

[MetroKindAGuy]

But , what if I have to gas way more frequently in 5th, as it acts like I'm lugging it? and takes much longer to get back to 50ish from 45 (my low speed in my P&G)?

It's almost like I'm over geared at the target speed range.(43-52 mph)

thats why I mentioned I don't have the stock tranny for a vert, but from a lighter 4 dr metro.


I am sure in my metro, changing to 12 inch tires, would make 5th a better choice in my target range. But when I do drive the interstate, I would have higher revs.

Another question... Is 3000 rpms the best in all gears or just 5th?

Thanks for your HO, Navy

[smvssd]

Accelerating slowly and keeping your engine RPM's low are the best way to get the best gas mileage. Keep an eye on your tach and if you have a newer car they often give the instant gas milage. It takes practice but once you get it right you will be able so save a lot of money on gas.