Basic questions for fuel effiency
 

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.

it depends on what car you have as to what rpm you should be in for what gear

I have a 91 Sprint but since I have no tachometer, the exact RPMs do not matter, I am just looking for general principles.

drive nice and easy. try to keep revs low. don't skip gears.

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

Owners manual should have some info on shift points. May be copies online for download.

How much gas to apply: That can be tough to learn. Especially if you're starting out uphill. It sounds like you've already experienced both extremes, so try to find a happy medium. Wish I had more info for you, but this you'll have to learn on your own.

When to shift: It's going to be a bit tougher without a tach - at least at first. As far as shift points, try to hear when the engine sounds like it's doing too much work for the speed it's going. If you shift too early the engine will lug - that is, it will have very poor acceleration and will sound like it's struggling. It might make a 'put-put' kind of noise. You'll know. Lugging is pretty bad, so try to keep your engine at a healthy rpm. Just remember that if you need to accelerate quickly for some reason, you may need a lower gear.

Gear selection: I'm not a huge fan of skipping gears. Sure, you can blast first gear and then jump to third, but it's better to stay in the power band and use each subsequent gear as it was intended. Just go in order when accelerating, and when you're up to cruising speed try to hold the highest appropriate gear for the speed you are traveling, again avoiding any lugging of the engine.

I hope this helps. I'll try to chime in if you need something clarified or have any further questions.

Ah, before I forget. Here's a stick driving tip that my dad taught me, which he got from a driving school owner. Not one of your questions, but it was extremely useful when I was learning. A good way to get used to your clutch's friction point (that is, where it engages) is to pick an empty parking lot, put it in 1st, and then slowly release the clutch until the vehicle starts to crawl forward. No lurching. Keep it nice and smooth. Finding this point is crucial.

What you do with the kinetic energy you have at the top of an acceleration is more important than how you get up to speed. (Within reason, don't lug it and keep out of enrichment) If you can avoid the brakes you won't be wasting fuel used to accelerate.

I skip gears to get into 5th if a lower gear is not needed to get up to speed. Going up hill I go a little farther into the gear (let the engine rev a little higher) Going down hill I shift up sooner.

Instantaneous fuel consumption information is very key, an MPGuino or the like will help a great deal.

The method I use is to push the throttle in until the rate of acceleration stops increasing then back off a fraction.

I think you "don't skip gears" guys are wrong. I can oftentimes easily go 1-3-5. Less shifting = less high rpm operation, less sudden engine decelerating cycles, etc.

In fact, GM had "skip shift" logic in Corvettes for the express purpose of saving fuel.

I knew that if enough people weighed in, we'd give conflicting advice. :)

I agree that the original owners manual prolly had shift point info. might even have a "do not exceed" and a "for best economy" shift point.

In my cars I accelerate slowly and just guessing (since I don't have a tach) I'd say I shift in the 2000-2500 rpm range. For best efficiency always shift to the next gear as soon as possible without lugging the engine. Most of the time I go straight through the gears 1,2,3...., but occasionally I will go from 2nd to 4th if I'm on a downhill incline and can do so safely without lugging. Using this method I can usually beat the old EPA highway rating in mixed city/highway driving and on the highway often beat the old EPA highway rating by 5-10mpg. You want to engage the clutch at as low rpm as possible to prevent excessive clutch wear. The last clutch I replaced in my '88 Escort had 260K miles on it and the current clutch has over 200K miles on it.

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. :thumbup:

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.

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)

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. :thumbup:

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.

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.

OK! I think I understand most of it.

I'm looking at this graph for example:
http://ecomodder.com/imgs/geo-1L-bsf...nstruction.gif

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.

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?

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

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

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.

Current ecomodder opinion is that this is generally false. It keeps you in the low efficiency part of the bsfc graph.

However, astoundingly few people have actually tested it.

I've actually tested it with the help of one of my friends, using my ScanGaugeII, I didn't write down anything to make it official, but there is a slight improvement by "higher load" acceleration compared to slow steady acceleration when going onto a highway. BUT, slow steady acceleration is better in the city when you can't always predict a stop, or there are short distances between stops.

I try to use the term 'situational acceleration' because of how frequently traffic and conditions impact acceleration rates.

But, when it comes down to the open road, that's another thing.

JoeNavy - were the results substantial enough to overcome external variables? I'd be curious to see the results of a test on this. Reminds me of something the EPA did a while back if I'm not mistaken.

If I buy the SG-e, maybe I'll try a little A-B-A...

I will attempt an in depth when I eventually get an mpguino. Might be a little while though.

Lol. 2 days ago before I left town (in a different vehicle), the fuel gauge was almost at empty, so I had "fill up tank" on list of things to do. I was having nightmares of 25mpg on my geo metro. :p

Today when I started up it was showing just below half full. O_o After flopping back and forth during my errands, it was like 1/4 full when I stopped at the same pump that I used last time. Turns out the official number was 48 mpg which I can't complain about for learning to drive standard and hence purposely forgoing any hypermiling techniques. Extra loving my car already, but I think the fuel gauge will drive me crazy. :)

Still wish I knew how to use these BSFC charts to my advantage. :confused:

Here's how I interpret the BSFC charts. If you're on the gas, put it in the efficient zone. Approximately 1500-2200 rpm and ~75% throttle. In most cases that makes you accelerate. So you hold that zone until reaching the upper speed limit (either legal or self-imposed). Then go to neutral and coast for a while. I do engine-off coast which saves even more fuel. Then get back in gear (bump-start if EOC) and do another pulse. Repeat repeat repeat...

I find slightly better results at lower rpm - centered at 1700 or so - instead of the 2000+ the charts usually show.

48mpg is a good start.
But it certainly can be improved upon.

Forget about the fuel meter if it's not working properly.
You know how much fuel it's using, you now how much fuel goes in, and you know how far it's gone since refueling - that's all you really need to know ;)

The low-fuel light might still be useful though.

The chart I linked seems to show 3000 RPM as the best?

I don't understand, if I am at 3000 RPM, how do I know if I am at 25, 50, or 80 torque? :confused:

Unfortunately I'm still not sure of how fast to rev and shift gears for best efficiency but my next tank will probably be significantly better since I was driving slower, not speeding in general, and driving without breaks for all my trips today. :thumbup:

I think P&G is something I will never bother with.. to much work and boring. EOC I haven't tried yet, just coast in neutral so far, seems like a pain to turn engine on and off without a start button and have music cutting in and out. :rolleyes:

I am thinking to test a new hypermiling technique: getting out at stops and pushing the car fast enough so I can skip 1st gear entirely. Just won't work going uphill.

It shows good BSFC within that 283 line, which outlines a whole area from 1500rpm up.
I'd say you're OK from 2000-2500 at 70-85% load, so try accelerating in that area and see what results that gives.
If it still works, try shifting even earlier.

Aiming for the small 250 g/kwh window itself during acceleration seems futile.

Remember :
While you may get good BSFC, i.e. good power / gallon, you still get lousy mileage, so try to switch to steady driving (or P&G) as quickly as possible.

You don't really know, though you could try to relate it to the % loading of the engine (LOD gauge if you have a ScanGauge).
Gets complicated fast though, as it varies with rpm.

My "how to shift" opinion:

When shifting into the next gear, there should be NO CHANGE in RPM when letting the clutch out and accelerating. In other words, when the clutch is pressed in and the engine RPM drops, after you shift gears and let the clutch out, the RPMs should be matched and not change. The RPMs should not drop, nor increase when the clutch is all the way out. Shifting like this you can easily put 300,000+ miles on a clutch. If you have to replace your clutch before 100,000 miles, you are shifting wrong.

There should be NO throttle while the clutch is [disengaged] or even partially engaged- only apply throttle AFTER the clutch is completely out. The ONLY exception is on initial acceleration from a dead stop - let the clutch out just enough for the engine RPM to drop slightly, apply easy throttle, let the clutch out, THEN apply 70-80% throttle, but not so quickly to be spinning tires! You can do this when starting out on hills also without rolling backwards and slipping the clutch.

Yes, I will have to make a video on this. I have been meaning to do a hypermiling series.

Acceleration should be just before open loop on fuel injected engines, which is somewhere around 70-80% throttle. Here's the catch though: If you are driving stoplight to stoplight, then slow acceleration is best. If you are driving in rural areas, you should use that 70-80% throttle as long as you have more than 3 miles between stops.

There you go.

If you don't have a gauge, aim for something just above 1/2 and you'll be pretty good. There is a range that's pretty good, not just a single point. If you want to really fine-tune it you need a gauge. A vacuum gauge would help, too. 75% load roughly matches with 12 psi MAP (where 14.7 is ambient or engine-off).

Many bsfc charts are centered at lower rpm than the one shown above. Try this:
http://ecomodder.com/forum/showthrea...-got-1466.html

Again, my personal experience is that low rpm has its own advantage so you're better off keeping it on the lower side of what the charts show.

That being said, you're driving a Metro. That's a tiny engine. It may be that it does better at higher rpm than my 1.6.

Faster acceleration isn't a problem, as long as you follow it with an efficient glide. If you're accelerating to a too-high speed and have to brake for the next stop, that's extra speed you didn't need and you wasted the extra gas.

I do all my accelerations at about 80%. I don't have a single clear three-mile stretch on my commute. There really is more magic in the glide than in the pulse.