i thought you're supposed to coast as much as possible IN GEAR so that while on the decel using engine braking, your engine is using no gas.

i could be way wrong but that's what i thought i remember hearing people say. if you coast out of gear (in neutral) you are using the gas to keep your engine running at idle where if you coast in gear it's basically just your gears turning that's keeping the engine running and no fuel is being used.

anyone else know what is better? coasting in gear or out of gear??

 

Its actually not about doing JUST one or the other exclusively. As a driver, you have to utilize both methods to your benifit .

For example, I'll leave it in gear if I'm going down a small hill, but knowing there is either a stop-sign, or stop light at the base/bottom of that hill. By having it in gear, I'm not using any gas just coasting down the hill, however it gives me precautionary element of having the car in gear(if it was in neutral, I'd be going even faster down hill... and if there is a yellow/red light I'd have to slam on my breaks, or put it in 2nd to downshift

..... on the other hand, there is a realitively small hill that I occationally drive up/down. When I'm about to come DOWN it, I'll initially keep it in gear(4th) , but just as I'm close to being at the base I'll kick it into neutral >>>> as there is a stop sign a 1/4 mile down the road, and the road is flat (no cross walks... usually a very mellow road). Well, if I had it in gear, and tried to coast in gear without touching the gas I wouldn't make it to the stop sign(not enough speed/momentum to maintain a decent speed the 1/4 mile). Having it in neutral gets me to the stop sign going the speed limit, yet my scan guage says I'm averaging 188 mpg during that 1/4 mile streach

 

Hypermling is like a real-life video game for me. I enjoy the challenge of tweaking out high mpg numbers.

I spent half of yesterday refining my xB's Pulse & Glide efficiency. Following figures are with a calibrated ScanGauge, so they should be pretty close to actual. I don't do nearly as well in real-world driving - probably 15 MPG worse, in fact. But the following figures are really achievable. If I had a regular commute route, I could probably post some killer numbers, but being retired, I try new roads and new routes, and get lousy real-world figures.

5/4/09. Temperature 60 F, 15 mph south wind, dry roads. 9.8 mile roundtrip country road route with 1 stop halfway to turn around.

Driving With Load at steady 40 mph baseline 45.4 mpg

P&G 28-40 4th gear 90 LOD run 1 = 50.3 mpg
P&G 28-40 4th gear 90 LOD run 2 = 53.1 mpg

P&G 25-40 4th gear 90 LOD run 1 = 54.4 mpg
P&G 25-40 4th gear 90 LOD run 2 = 54.5 mpg
P&G 25-40 4th gear 90 LOD run 3 = 55.1 mpg

P&G 25-40 3rd gear 90 LOD run 1 = 51.5 mpg
P&G 25-40 3rd gear 90 LOD run 2 = 53.1 mpg

P&G 25-40 4th gear 75 LOD run 1 = 55.3 mpg

P&G 25-40 4th gear 83 LOD run 1 = 57.2 mpg

I ran the 75 and 83 LOD runs at the end, along with run 3 of the 90 LOD. The 83 LOD run is the standout winner. The runs don't differ much relatively from my initial tests with the uncalibrated scangauge. 28-40 and 28-45 mph surprised me, as the Scion lugs the engine accelerating at 90 LOD from 25 mph, and its more on the power curve at 28 mph. I have to start with about 70 LOD at 25 mph, and gradually increase the power to 75, 83, and 90 LOD for my tests.

Third gear results didn't surprise me. The engine is turning too fast at 40 mph in 3rd.

Note my worst P&G results beat a steady 40 mph DWL of 45.4 MPG by 10.8%, and my best P&G results beat it by 26%.

 

A great tool for trying to achieve maximum mpg is a simple vacuum gauge.
Far left:
Higher the vacuum, the better the mpg. It is amazing to see how little you need to push the accelerator to effect air/fuel delivery.

Also has anyone considered trying a a more narrow tire size? I know this goes against everything in the handling and safety issues so please no flogging. Just curious because I went from the stock 185 to a 195 on my Brides B, and her mpg went from upper 30's (33-38 ) to mid 30's (30-35 ) So tire size has a lot to do with mpg. 10 mm must make some difference. 175 60 15 are not an easy find either, but there out there.

Her high mpg is achieved by conservative take offs and trying to keep it under 60. No other tricks, 100% stock 5 speed.

 

Interestingly enough, a more narrow tire size = safer in wet weather conditions(you'd think the opposite) , but from what I've read since there is more PSI on a more narrow tire, there is less of a chance of hydro-planning.

My stock tires are 185/60 -15" , comfortable,and work great, for just about everything except for motor-X'ing :-)

 

So true, the take offs are key. I was able to achieve 38mpg last tank with granny take offs, and a feather foot, sitting on 205/50 16. Not bad

 

Actually, if you look at Brake Specific Fuel Consumption graphs, MT cars typically get better mileage with fairly spirited acceleration - provided you glide afterward. AT cars will slip and downshift when pushed, so driving like a grandma for best mileage applies to them.

 

so what is the verdict here...

is more fuel being consumed by the engine while coasting in neutral?

OR

is more fuel being used when the engine is coasting in gear while decelerating? (engine braking)

i always thought when you are decelerating in gear the only thing making the engine "run" is the gears turning it and that fuel is cutoff until applied again to accelerate or get to idle.

 

The answer is, it depends. Fuel cutoff (DFCO) occurs under open loop conditions above certain rpm, when the throttle position sensor is at idle. If the rpms are too low, TPS is too high, loop stays closed, or temperature is too low, you'll never enter fuel cutoff, and will continue to use fuel while coasting in gear.

That's balanced by how much farther you'll travel in neutral v. in gear. Since mileage is distance/mile traveled, you may come out ahead coasting that extra half mile in neutral v. having a short coast using no fuel, and having to power up to travel the additional distance.

If the hill is steep enough that I'll build up to a speed greater than the speed limit, then I'll coast in gear. Most of the time, the hills aren't that steep, and I'll glide much farther and faster in neutral. In fact, I've owned my xB for a month, and just confirmed today that it enters DFCO.

 

what RPM do you enter DFCO???

 

I wasn't monitoring rpms when it happened. i was monitoring loop condition, TPS, mpg, and current fuel consumption on my ScanGauge, and forgot to look at the tachometer.

On my SE-R, DFCO doesn't occur unless rpms are >2500, which means I have to be going about 65 mph in top gear, or I have to drop to lower gears at lower speeds. Once it's in DFCO, it will continue fuel cutoff well below 2500 rpm. I'm pretty positive the xB was nowhere near 2500 rpm at the time it kicked into DFCO. Many other cars will enter DFCO much more readily than my Nissan - some as low as 1000 rpm, I'm told.

 

I was surprised to see how much of a difference the outdoor temp makes... After that long winter, I just got my first 40mpg tank. I struggled to get in the low 30's when it was real cold here around Chicago.

A few more things noticed over time with the scangauge:
(AT 06 Pirelli p6 steelies snorkel removed irridiums partial grill block, crummy 10% ethanol gas)

For auto trans, while getting up to speed, you can ease up on the pedal for a moment to get it to shift earlier. The goal is to get into the higher gears quickly to let the engine loaf while keeping up .

It's FLAT here, so there isn't much use in the fuel shut-off/coasting in gear - it's better to watch ahead and just pop it in neutral if you see a slowdown coming.

By having the average trip mpg displayed, it's easy to see it drop during red lights/trains. I've started turning off the engine if I know it's going to be a while. (I think the break-even time is 10 seconds...)

Heavier traffic/ but not stop and go is the mpg friend, if you can pulse and glide - I still try and flow with traffic - I'm not hard core hypermiling!

Ron

 

Do you have/ are you using a Scan Guage 2 ?

 

Tires can effect a lot in a lot of different ways so just size won't necessarily effect it that much. Tire compound (silca blends run smoother with less effort), the hardness of the tire (the actual rubber compound) the efficency of the tread design (solid ribs around vs blocks) the actual tire casing effects ride, etc as well as side wall stiffness (as far as how much deformation there is and what the contact patch looks like)

That ethanol additive kills my mileage-like 2-4 MPG. Rain on the roads makes a huge difference too-I am guessing due to extra friction from the puddles (no matter how small) but also when it rains it's colder so there might be less air pressure too.

I got a lip spoiler for the front and once installed my mileage went up between 1-3 MPG-who would have thought. (there is a photo of it in my profile-the black lipped pic)

 

Keep in mind that winter gas has a negative effect on mileage too.

I was running 26-27 during the winter here and now I'm getting back to the 32 range I usually sit at.

 

[quote="snowromance"what RPM do you enter DFCO???[/quote]
I just confirmed today my xB enters DFCO above 1500-1600 rpm. That's about 35 mph in 5th gear. Below that point, no DFCO.

 

I just confirmed today my xB enters DFCO above 1500-1600 rpm. That's about 35 mph in 5th gear. Below that point, no DFCO.

 

Gas has been too cheap lately, I've been wasting it to hear my header and exhaust

 

http://ecomodder.com/ is very helpful.

 

Hey I was looking for tires for my 06xB and ws thinking that getting the Prius size tires 185/65R15 would result in about an inch taller tire effectively lowering the engine RPM in my 5speed stick and making the speedo accurate - (about 3mph high at 60). Tire Rack reports indicate that the Pirelli P4 have much better snow and rain traction than the stock Goodyear Eagle LS OEM tires and an xB user recommended them for snow use in the survey.

With the upgraded ScanGauge II software for this tank I am at 48.4mpg after a couple of days of 20mpg in town killer 0.5 mile trips but I was over 50 for the tank before that - only it is probably 9% high because I have not entered the fuel correction yet since getting it back from the upgrade. I did get 280 miles at the half a tank mark which is right up there for the 6 gallons burned. Seems I don't get much below 40mpg even on highway trips unless there is a head wind. Synlube has 22k miles on it without changing, tires a little over 40psi cold. Injector cutoff happens down to about 1000rpm as long as the engine is hot and there is no heavy electrical load or AC running. I get engine braking in 5th down to about 20mph then it bucks when the injectors kick back in. Don't even bother turning the engine off at a light - with the cost per minute at idle you burn about 1 penny a minute and the startup fuel burn rate is a lot higher - you are better off letting the engine settle down to the really low fuel burn rate of 0.11-0.12 gph than to shut if off and start it up again.