So thinking ONLY of fuel savings, in a manual shift car, when you are decelerating, I assume you are better off in a high gear then in neutral, right? This would make the engine take longer to slow down then it would with no load, right? And if it takes longer to slow down it would spend more time with no gas being sent to the injectors, right?
Ding ding! You’ve got it.
Johnny exactly right. As the engine slows down, when the engine speed get to the cut in point (Let’s say 1300 RPM for sake of our conversation) the ECM turns the fuel back on. So you back off at say 3,000 RPM there is no fuel until the ECM detects 1300 RPM and then fuel injection resumes. This is imperceptible to the driver. I can see it on my diagnostic tools, but the driver can’t feel it. If the driver opens the throttle, all bets are off and fuel injection restarts right away.
If any of you want to swing by the San Fernando Valley, I will be happy to demo it for you. 
Cisco Seriously, I am sorry, that was uncalled for snark, and I am sorry. Yours was a fair question, and I should have handled it with a bit more grace. I hope I answered it to your satisfaction.
Joey P On the head. The longer you can keep the engine revs above idle with the throttle closed, the more time the engine will go without fuel. This is a good thing from a MPG point of view.
Thanks, Rick
Um… ehm… erm… eh…
It was about 50 on the way to work this morning. I had my hot weather in New Orleans a few weeks ago. 
Have I mentioned I hate you?
You should pity me! Tomorrow it might get into the upper-70s! :eek: Working from home, so I don’t have a/c. I’ll have to have the door open and the fan on!
Bah. The forecast says 114 here tomorrow, but the weather channel always seems to underestimate.
Rick, you should get the mods to put a sticky up for you till the gas drops back below $4.00 again.
Think you missed what I wrote in brackets about burning rich at WOT! The economy “sweet spot” will be a mostly-open throttle, but still burning lean. (Or WOT, and an engine management that doesn’t inject extra fuel.) Advice to accelerate as gradually as possible IS wrong, although I can see where it comes from. Johnny L.A.'s “briskly” makes more sense, although it wouldn’t surprise me if his Prius never burns rich anyway.
As much as that? I had no idea. Doesn’t that conflict with emission standards?
matt yes as much as that. AFAIK all injection system have some type of full throttle /near full throttle enrichment. If they did not the car would be a real slug.
The problem you run into is finding exactly where the enrichment comes in. On some cars it comes in at 70% throttle or more. Calibrating your foot to open the throttle 69% and no more is difficult at best.
It does not interfere with emission standards as the converter can handle intermittent rich conditions, due to the oxygen stored in the cat. Even if you go Wide Fucking Open (WFO) getting on the freeway it is only a few seconds to get the car to speed.
For most drivers accelerating smoothly and evenly sing minimal throttle opening will out preform opening the throttle, backing off, (transmission shifts) opening the throttle etc. This is due to two facts. First off sooner or later the driver in the second condition will either push the pedal too hard and get into enrichment or will forget to lift his foot. Also with automatics throttle plate position is an input to the transmission. The further the throttle is open, the higher (RPM wise) the shift point is.
This is how I drive, and I regularly exceed the EPA numbers for my cars in both city and highway. I do not drive slow, I just drive very smooth and use the throttle as little as possible when accelerating.
But, in a manual transmission car, you can coast further in neutral than in gear. Where the “fuel need for idling/drift distance” tradeoff begins is the question though.
Even if I could pull off a miraculous 10 extra mpg by doing all the hyper-miling methods would I?
12,000 miles a year I’d save about $500.
I’ll pay the $500 convenience fee and drive how I like to thank you very much.
Works pretty well for me… Driving ‘aggressively’ (quotes, because I hardly ever drive really aggressively), I’d get around 40 to 45 miles per (UK) gallon. Driving ultra-conservatively, I can just about get 70mpg.
I’ll drive semi-efficiently and save $250.
Thanks Rick, you’re a mine of information on the car stuff! I guess I’m wrong.
I always thought you only burn rich to ensure you use every last scrap of the oxygen running through your engine. But if you’re adding up to 33%, are you also using the cooling effect of the extra fuel to increase the charge? Or is there some knock-related reason for it? Do you know offhand how much extra power you get burning that rich on WFO 
, compared with slightly lean?
Yeah, I guess you’re screwed there. The techniques of the Shell Eco-marathon don’t export directly to road vehicles! There are a few guys out there claiming to bust 100 mpg in normal cars using “pulse and glide”. Here’s one: http://metrompg.com/posts/xfi-pulse-and-glide.htm I’d much rather see consumption calculated using before-and-after fuel measurements, though, rather than the “scangauge” widget. And see what mileage he gets just driving at his average 22mph in high gear.
I drove much differently on my last tank of gas, just to see what would happen. Foot at or near the floor on acceleration, shifting at 3,500-4,000, etc. MPG went to 26.56. It seems driving habits don’t make much of a difference in my car. From average, to ultra-conservative, to pretty aggresive was a range of barely 2mpg.
I almost never let the revs (manual tranny here) drop below 3,000, for safety reasons. Yeah, I could chug around town at 45 MPH (most common non-highway speed limit here) in 6th at 2,000 RPM, but I’d lack any sort of instantaneous oomph if I needed to accelerate quickly, for whatever reason. I’ll gladly trade 2 MPG or so for that extra margin.
I’m going to touch on just one issue, tire pressure. Over-inflating to the max safe pressure will reduce rolling resistance. However, it also slightly increases thee tire circumference, which fools the speedometer/odometer into showing fewer miles than you actually travelled. Your calculations at the fillup are based on that mistaken mileage, and your mpg will disappoint you.
To get the actual miles travelled with rock-hard tires, you have to get all mathy.
Track your daily commute simultaneously with your odometer and a GPS, then find a ratio. OR
Drive a known distance twice, once with recommed pressure, and once with bangy pressure. Find a useful ratio.
Without starting a debate over coasting in neutral vs coasting in gear (that’s a thread on it’s own, and we’ve done it already), I was thinking specifically about coasting off the freeway to stop at a light at the bottom of the off ramp. Since I know my car will make it that far in neutral or any other gear distance wasn’t a concern.