So running WOT is the most efficient for the engine...

[fuzzybabybunny]

Does that mean that in order to get the best fuel mileage, I should be accelerating WOT (ie. balls to the wall, accelerating as fast as I can) up to my intended speed and then just shift to my highest gear and cruise?

Say I want to cruise at 50mph. I start at 1st, floor it and redline it to 30mph, then shift to 2nd and floor it to 50mph, then shift directly into 5th and cruise? That would be the most fuel efficient way to drive?

 

[waffleironhead]

Are you assuming that the added stress and wear from running your car like that will be made up in fuel savings?

 

[fuzzybabybunny]

Are you assuming that the added stress and wear from running your car like that will be made up in fuel savings?

No. I've just heard that WOT is the most efficient and was wondering if driving like this is what those people mean.

 

[Demo24]

There is a difference between engine efficiency and fuel efficiency. For example an engine is running the most 'efficient', aka output wise, at WOT. Running at WOT does not necessarily mean you use less fuel. BMW awhile back did find it somewhat more fuel efficient to go WOT, but shift at like 3k. Redlining it like that will give you a noticeable mpg hit.

 

[PlasmaBomb]

No.

Running at WOT is most efficient at making POWER, it's not necessarily most efficient at fuel consumption (I think most stock tunes run slightly rich at WOT, from what I'm told).

Look up brake specific fuel consumption, it has been posted before.

 

[ElFenix]

iirc, the most fuel efficient is to accelerate hard and continually short shift until you get up to the highest gear for your speed. this minimizes pumping losses and gets you into your most fuel efficient configuration as quickly as possible. supposedly BMW put its stamp of approval on this technique.

 

[slugg]

I've found that the more you can stay off your brakes, the better your gas milage.

 

[DVad3r]

I think the most efficient is to shift at peak torque, etc. Obviously shift a bit later when going up an incline. WOT shifts are definitely not the most fuel efficient rofl.

 

[Bignate603]

I've found that the more you can stay off your brakes, the better your gas milage.

This. You can spend all day trying to figure out where your engine runs most efficiently but you'll get better gains just by minimizing the amount of power that you throw away braking. If you take your foot of the gas earlier and coast up to a red stop light you'll save gas and wear and tear on your brakes as well.

 

[Fenixgoon]

using WOT is the most energy efficient, i.e. maximizing work output / energy input

being the most fuel efficient (mpg) is not necessarily also the most energy efficient.

 

[soccerballtux]

it's not most energy efficient.
Most cars at WOT enter an open loop state to keep the engine thoroughly within the "safe" area.

Do what works for your gas mileage the most. For me it didn't make sense. Accelerating quickly but gently makes most sense for my car.

If you have a wideband sensor on the exhaust and a tune, the WOT efficiency will be much better.

 

[soccerballtux]

when I want to be "fast/inefficient" I usually go 1st 2nd and then floor it to 6k redline (lol) and shift straight to 5th. Horrible consumption during that acceleration, but I get there so fast and go straight to 5th it doesn't actually hurt mileage that badly.

 

[WhoBeDaPlaya]

This. You can spend all day trying to figure out where your engine runs most efficiently but you'll get better gains just by minimizing the amount of power that you throw away braking. If you take your foot of the gas earlier and coast up to a red stop light you'll save gas and wear and tear on your brakes as well.

+1 The bonus is, you'll actually pay more attention to what's ahead / further up ahead.

 

[exdeath]

It's sort of like a jet engine. Yeah it's the most efficient thing there is when you need 55,000 lbs of thrust, but you wouldn't put one in a Prius to get maximum MPG.

 

[vshah]

It's sort of like a jet engine. Yeah it's the most efficient thing there is when you need 55,000 lbs of thrust, but you wouldn't put one in a Prius to get maximum MPG.

http://www.ronpatrickstuff.com/

 

[exdeath]

http://www.ronpatrickstuff.com/

I said a 55,000 lb thrust engine :awe:

Anyway, it's about time. I always wondered why nobody was looking into tiny gas turbine-electric hybrids. Perfect application for the constant RPM, power to weight, etc.

 

[thomsbrain]

It's WOT combined with lowest possible RPM. So go WOT and then shift as early as possible without stalling in the next gear. Repeat. Profit. Depending on your car, you may be shifting at RPMs at or below 2,000. Hypermiling 101.

 

[JCH13]

I'll throw in my $0.02 here...

Running almost WOT (say 85%, maybe 90%) near your engine's peak torque RPM is an efficient way to accelerate your car. That is typically where an average engine's BSFC (brake specific fuel consumption) is maximized. This means that you're extracting the highest fraction of useful energy per unit of fuel consumed possible.

Then shifting into the highest gear possible once you're at speed is a good idea and should result in decent fuel economy.

To the best of my understanding SAE Supermilers (an SAE competition) run their engines at near full-power while they are accelerating to a certain speed, then shut off the engine and coast down to nearly 0mph before starting their engine again and accelerating back up. It's a great way to get high fuel economy, winners get over 2,000mpg, but not very practicable on public highways.

 

[soccerballtux]

It's WOT combined with lowest possible RPM. So go WOT and then shift as early as possible without stalling in the next gear. Repeat. Profit. Depending on your car, you may be shifting at RPMs at or below 2,000. Hypermiling 101.

no as I said, many cars dump up to 30%+ extra fuel in at WOT on top of what is required to reach stochiometric ratio. This is why when I tried shifting ASAP at full throttle, it still hurt my gas milage by about 15-20%. Better is to just drive normally or slightly zippy.

Each person will have to test their own car.

 

[overst33r]

Running 80-90% of WOT at the lowest bsfc will get you the best MPG. Depends on the engine, but usually that's between 2500-4000rpm on a gasoline engine.

 

[IGemini]

Yeah, it's moderate driving combined with low RPM and minimal braking. Just in the example of a Cruze I drove lately, I've seen a difference of ~5 MPG doing town driving from just shifting to a higher gear. Automatic overdrive works on the same principle. WOT is NOT efficient, handling a vehicle like a race car by redlining and aggressive braking will bleed efficiency like a sieve.

In the case of cars with "higher" engine power (my Impala "LS" for example), mileage can be better at higher speeds for long distances, though not as significant. By this I mean some flow-of-traffic highway speeds (i.e. over speed limit) might get another 1-3 MPG, depends on the car and distance traveled.

 

[Bignate603]

Anyway, it's about time. I always wondered why nobody was looking into tiny gas turbine-electric hybrids. Perfect application for the constant RPM, power to weight, etc.

It's not as easy as perfect as you think. Turbines get more efficient as you increase their pressure ratio and their turbine inlet temperature. It's hard to get a higher pressure ratio in a small turbine, especially with a compressor that doesn't have crappy efficiency. As for turbine inlet temperature, as you push the temperature higher you end up needing expensive cooling schemes and pricey materials.

You can get an efficiency boost by going to a recuperated cycle (use exhaust gas to preheat the air between the compressor and combustor) but that adds even more cost. People are still trying but they're having a hard time getting to a piston engine's efficiency without making the turbine very expensive.

The claims in that article are a pipe dream. There's no way you're going to get that in a tiny little engine, with turbines it's easier to get higher efficiencies as the turbine gets bigger. A 60% efficiency in a gas turbine is incredibly high, they barely touch that in the massive gas turbines used in power plants and those take a combined cycle to get that high (they use the exhaust's heat to boil water which is put through a steam turbine to squeeze out more power).

 

[HeXen]

i often pop my tranny into neutral and coast for a ways to a stop. dunno if it helps mileage, but figured it couldnt hurt compared to maintaining speed up to the point where you need to brake firmly like most do.

 

[overst33r]

i often pop my tranny into neutral and coast for a ways to a stop. dunno if it helps mileage, but figured it couldnt hurt compared to maintaining speed up to the point where you need to brake firmly like most do.

or you could be safe and still save gas by coasting in gear.

 

[HeXen]

coasting in gear slows me down too much. i can cruise for quite a ways in N without losing much speed. at least in my Civic anyway. i already stated i didnt know if it saves me gas or not. i honestly didnt care either.