MPG is all I care about...

I’m thinking the new Prius may be a sellout success and if it does sell in high numbers and manages to convert a lot of pure ICE drivers with its looks and performance to a hybrid or plug-in is that really so bad for the planet? Yes they could have uglified it and kept the 1.8l engine with 15” wheels to get a substantial improvement in fuel mileage but how many converts would you get with that?

 

Yes, its CdA , supposedly equal to about 6.2 ft² for the 3rd generation. Probably a little lower for 4th.

 

That's been losing converts.

 

I mentioned this in another thread, but the higher output motor may make it far easier to stay in 'glide' mode for a longer time than previous models. 'Gliding' with the engine off as we all know is how you achieve very high MPGs around town and at low speeds.

This is why I'm waiting to judge until we get some real world MPG numbers from folks that are interested in MPG vs. the "boy is this fast for a Prius" reviews we have been seeing all over the place.

 

If two engines have the same efficiency then it doesn't matter how poweful the engines are or long the glide will be. More power just means it gulps down more fuel for a shorter pulse but then makes up for it in a longer glide. The more powerful engine would have to be more efficient during the pulse to get the same fuel mileage.

Take these theoretical examples in the same car body that takes 20hp to maintain 60mph:

1. This one has an engine that's 40% efficient at 20hp, so you maintain a steady 60mph but are 45% efficient the whole way.
2. This one has an engine that's 40% efficient at 40hp, so you pulse half the time and glide half the time to stay around 60mph. The pulses take twice the amount of fuel but are made up for in the glides that you don't have room for in the first car.
3. This one has an engine that's 40% efficient at 80hp, so you pulse a quarter of the time and glide three quarters of the time. The pulses take four times the amount of fuel as the first car, but are made up for in the longer glides.
4. This last car is 40% efficient at 160hp, so you pulse one eighth the time but it sucks down 8 times the fuel in those pulses than the first car. But since most of the time you're gliding you still average out to exactly the same fuel mileage as the other three cars.

 

Uhh...I think we are talking about two different things.

When I say 'glide mode', I mean gliding in EV mode with the engine off. You know...when you do the pedal motion to cut the engine and 'glide' while the engine is off. It is a very well know hypermiling technique. A more powerful motor and higher output battery will help that immensely.

Personal note...my "test circuit" has always been a slight incline that approaches our driveway on my commute home. None of our hybrids have been able to make it up this incline under electric only power without REALLY playing the pedal lightly to prevent the engine coming back on. While doable, it isn't practical...the electric motor and battery output just isn't powerful enough. This is coming from a Prius V wagon, 3rd gen liftback, and a Prius C. The Prius C is the easiest due to it's very low weight, the 3rd gen liftback comes in second, and the V wagon is a distant third ( this thing is an underpowered, high weight, beast ). I'm hoping the 5th gen Prius will be the one that can easily achieve the dreaded incline.

 

Hah, I've got something similar, just a stretch of road with a slight upgrade. I can easily make it through in electric-only, with our 15" snow tires, Michelin X-Ice. With the stock 17" Michelin Primacy MXM4 on the heavier alloy rims, it's borderline.

 

pulse and glide aims for neutral in the glide segment. no engine, no motor, no regen

 

Yep..except that in the case of a hybrid, the glide phase is/can be 'assisted' by the electric motor.

 

It looks like we're talking about the same thing to me. Cut the engine and glide in neutral. See Bisco's description.

The point is, yes, with a more powerful engine you get to "gliding" mode quicker, but on the other hand you use more fuel during the "pulsing" mode because more power means more fuel per mile. In the end it evens out to whatever the actual efficiency of the engine is. Power is (generally) irrelevant to pulse and gliding other than it's harder to pull off the more powerful the car is.

I've been hypermiling gas cars since I was a kid. I'm not doing very well in the Avalon right now, but I that's mainly because the blasted thing goes into "engine warm up mode" for several minutes which consumes a lot of fuel, and then is finally ready to do it's hybrid thing about the time I'm at my destination. Too short distances, too cold weather.

I loved driving manual cars and doing the same thing (albeit, illegally). I'd shift into neutral and coast a good bit, letting my speed drop by half. Then I'd put it in top gear, pop start it, and slowly speed up (hey! we're talking 50hp, tops) to my top limit speed and start all over.

I loved my VW Beetle too as it had an idle shut off valve. When engine braking I'd switch the ignition off and on really quickly which would shut the valve, but the intake manifold vacuum would keep it closed until it reached idle speeds or until I blipped the throttle. Those were the days!

 

I get what you are saying now and agree. Yeah...I have been hypermiling a long time as well. Haha...I did exactly the same neutral trick with my manual Honda Civic VX back in the day. I pulled off some incredible MPGs...but admittedly the engine was really poor with emissions.

However, as you well know, there many more variables than just "the engine". In my opinion, the weight of the vehicle has an even larger impact. For instance, the Prius C has been by far the easiest to 'glide'...even though it has a tiny engine, battery, and motor. It is the incredibly low weight ( compared to other modern cars ) that makes it possible ( the 2012 Prius C is only 2500 lbs....the 2012 Prius V is 3274 lbs ).

 

Yes, weight is a factor. Sadly cars just keep getting heavier.

What's worse is aerodynamic drag, at least at highway speeds. Yet people love the utilitarian style, the exact opposite of aerodynamic. Generally speaking, the more aerodynamic a vehicle is, the more it starts to look like a plane without wings, not a tall brick.

 

Second @fuzzy1's link. That is one of the hypermiling bibles.

One of the earliest write ups for pulse and coast was in a 1950s Popular Mechanics. Engines in traditional ICE cars are sized for the sometimes of jobs of passing and climbing, leaving the majority of their operation at lighter, less efficient loads. The theory is that the pulse puts the engine at the higher load, where it is more thermally efficient, until the target speed is reached. Then let the car coast down to a low speed, at which point the pulse is repeated.

Done correctly, the heavy fuel consumption of the pulse and idling consumption of the coast adds up to less than driving the car normally at that average speed. It's actually easier to pull off with a more powerful car, it is just that the absolute results don't look as impressive.

Driving with load is easier to practice in traffic. With that, you pick a speed, and hold the accelerator at the point to maintain that speed on a level road. When the incline changes, don't move your foot. Let the car slow on uphills, and gain speed on the downhills.