Originally Posted by Znod' post='227429' date='Jan 21 2006, 09:24 AM

Hi Friends:

I have described my driving procedures before--which coincide for enjoying my car and for good mileage. I aways drive in DS--using a combination of manual and automatic shifting--with the emphasis on manual. I tend to get up to speed pretty quickly usually letting my engine get to 4k or 5k RPM before shifting. In this regard, I tend to maximize the time that my instantaneous MPG meter shows 20 MPG or better. It turns out that there is an explanation of why the rapid-acceleration part of my procedures may work. So, from Road and Track November 2005 we have:

"Full-Throttle Economy

If piston engines are most efficient at full throttle, won't we maximize fuel economy by flooring the pedal after every stop to get up to cruising speed? Or indeed any time we want to increase speed? (This is contrary to conventional wisdom which says that gradual acceleration is the best way to maximize economy.)
David Bookstaber
Berwyn, Pennsylvania

To oversimplify, yes. Given the practicalities of real engines, accelerating at three-quarter throttle (enough to reap a reduction in pumping losses but not enough to invoke wide-open-throttle fuel enrichment) returns excellent mileage. But in the real world of crawling traffic, such a rapid gain to cruising speed is not always practical. Also, this technique often results in acceleration to an unnecessarily high speed (especially between stoplights and other closely spaced impediments)."

Originally Posted by Bimmer32' post='227638' date='Jan 21 2006, 05:12 PM

Are you saying to start the car in 4k-5k rpm is the most efficient way? It appears that when I drive 48 mph (per the mpg rating), my rpm is at around 2k range. Wouldn't that be the most efficient rpm range?

Originally Posted by Trev550i' post='227534' date='Jan 21 2006, 03:27 PM

so you always drive in ds mode znod and accelerate fairly quickly? Do you have to replace the brakes more often?

Originally Posted by EBMCS03' post='227640

Are you saying to start the car in 4k-5k rpm is the most efficient way? It appears that when I drive 48 mph (per the mpg rating), my rpm is at around 2k range. Wouldn't that be the most efficient rpm range?

Originally Posted by Bobbin-Man' post='227443' date='Jan 21 2006, 11:21 AM

I worked this out a few years back in my e39 and it really does return pretty good economy figures.

I've concluded that it simply is based on the fact that the increased engine efficiency as revs increase rapidly is more than the addition fuel used to reach the desired speed, ie. get the acceleration bit out of the way quickly then you can get on with economical driving. Doesn't half make driving economically more fun

Originally Posted by Peter530i' post='227462

Well at least now when my wife asks my why I drive the way I do, I have something to come back with besides "'cuz it's fun!"

Originally Posted by Bimmer32' post='227655' date='Jan 21 2006, 07:31 PM

If I accelerate to 4-5k rpm every time to cruising speed, I'm going to hit every cars that's in front of me.

Originally Posted by tab545' post='227559' date='Jan 21 2006, 04:32 PM

I thought I had heard something about the Valvetronic Double-VANOS system in the 545 reducing these pumping losses.

See the attached, http://www.bmwworld.com/technology/valvetronic.htm, which talks about this engine's reduction of those typical partial-throttle power losses.

So the point may still be true, partially, it may not make much difference, or any, on my car.

But I won't tell our wives if you won't. I like an excuse for the jackrabbit starts, too.

Originally Posted by Mr 5er' post='227613' date='Jan 21 2006, 07:21 PM

Well I see I learn something new, each and every time I read this forum. Good info....thanks