Getting Better Fuel Mileage (Trucks)

Tech questions that don't fit above forums

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Re: Getting Better Fuel Mileage (Trucks)

Post by MadBill » Wed Jan 02, 2013 10:38 pm

I know it sounds implausible, but it's true. (see below, from Wikepedia) For example, many years ago I helped a friend win a Corvette Club fuel economy run in his '72 350 M/T. With no prep other than 50 psi and full Hypermile driving, he averaged almost 60 MPG. It's a major part of the unlimited F.E. contests such as the Shell Eco-Marathon where the most recent winner averaged almost ten thousand MPG.

Also, it's not necessary or even advisable to accelerate in too high a gear or to excessively short shift, as using more revs to accelerate faster means less 'burn time' and more 'coast time'


"Burn and coast
Burn and coast is also known as pulse and glide. This method consists of rapid acceleration to a given speed (the "burn" or "pulse"), followed by a period of coasting down to a lower speed, at which point the burn-coast sequence is repeated.[28] Coasting is most efficient when the engine is not running, although some gains can be realized with the engine on (to maintain power to brakes, steering and ancillaries) and the vehicle in neutral, or even with the vehicle remaining in gear[citation needed]. If a manual transmission vehicle coasts with the engine off, it is typically restarted by disengaging the clutch. The engine control units of some vehicles command a richer fuel setting immediately after the starter is activated, so the bump-start manual transmission vehicle will typically achieve the best fuel economy gains.[29]
Some hybrid vehicles are well-suited to performing the burn and coast. In a series-parallel hybrid (see Hybrid vehicle drivetrain), the internal combustion engine and charging system can be shut off for the glide by simply manipulating the accelerator. However based on simulation, more gains in economy are obtained in non-hybrid vehicles.[28]
[edit]Why "pulse and glide" saves energy
Much of the time, automobile engines operate at only a fraction of their maximal efficiency, resulting in lower fuel economy (or what is the same thing, higher specific fuel consumption (SFC)).[30] Charts that show the SFC for every feasible combination of torque (or Brake Mean Effective Pressure) and RPM are called Brake specific fuel consumption maps. Using such a map, one can find the efficiency of the engine at various rpm's, torques, etc.
During the pulse (acceleration) phase of pulse and glide, the efficiency is near maximal due to the high torque and much of this energy is stored as kinetic energy of the moving vehicle. This efficiently-obtained kinetic energy is then used in the glide phase to overcome rolling resistance and aerodynamic drag. In other words, going between periods of very efficient acceleration and gliding gives an overall efficiency that is usually significantly higher than just cruising at a constant speed. Computer calculations have predicted that in rare cases (at low speeds where the torque required for cruising at steady speed is low) it's possible to double (or even triple) fuel economy.[28]
These two- or three-fold improvements in fuel economy are possible only at city driving speeds of say 25 or 35 miles/hour. This is because cruising (steady speed) at such low speeds is very inefficient since the torque needed is so low that the efficiency read on a BSFC map is very poor. Pulse and glide significantly improves this. Unfortunately, city driving often involves many stops at signals and stop signs which were absent in the computer simulation which showed such multiple fold improvements. In other words, in the real world one is unlikely to see fuel efficiency double or triple. Such a failure is due to signals, stop signs, and considerations for other traffic; all of these factors interfering with the pulse and glide technique. But improvements in fuel economy of 20% or so are still feasible.[28][31]"
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Re: Getting Better Fuel Mileage (Trucks)

Post by Matt Gruber » Thu Jan 03, 2013 2:40 pm

The tires are rated EXCELLENT ROLLING RESISTANCE by consumer reports. 1/2 mile to coast 45 to 20 sounds amazing to me, but i never tested any car before. Very quiet, like an electric car :lol:
The reaction from other drivers was not what i expected. It solved the problem of someone following too close! Once it drops to 35, drivers go around. So NOBODY is anywhere on my tail at 25, it is like i own the road.
Previously there would always be somebody close, makes me worry they will rear end me, as i turn on my street. A 61 has 49 chevy steering, so it can't take a corner at modern speeds :lol:
Note, i coast down only, no crazy accelerating as drivers pass me.
Thanks for the replies!
.
.
tame a lumpy cam for the street, more street torque! see my article, archived in the waybackmachine.
https://web.archive.org/web/20130707064 ... TGRU/carb/
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Re: Getting Better Fuel Mileage (Trucks)

Post by PackardV8 » Thu Jan 03, 2013 4:31 pm

A 61 has 49 chevy steering, so it can't take a corner at modern speeds
That'd be news to those of us who raced them back in the day and to those still running in vintage racing today.

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Re: Getting Better Fuel Mileage (Trucks)

Post by Matt Gruber » Fri Jan 04, 2013 6:28 am

Wow Jack
so u can keep up with c5's and c6's?
with stock 61, 5" wide wheels? and 205/75/15 tires?

Isn't VINTAGE RACING for cars that CAN'T keep up with a current design?

And what does racing have to do with ordinary street driving?

and since the topic is fuel mileage, how is the MPG while vintage racing?

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Re: Getting Better Fuel Mileage (Trucks)

Post by MODNROD » Sat Apr 06, 2013 10:11 pm

Well bugger!
Here I am surfing to find out more about aero aids, looking towards trucks obviously with what works and what doesn't, and SPEEDTALK (?!?!?!?!?!?!) of all places has a thread on fuel economy, hypermiling, aero trucks, etc. :lol:

Has anyone here had practical experience with using Vortex Generators to "fill-in" the aero gap between truck cab and the first trailer? On the back of the last trailer to reduce aero drag?
Would a series of laminar lips do the job as well or better I wonder?

I'm hoping to fill the aero gap between the fairing/screen to behind my back on my little scoot to improve fuel economy (it's a bit of a game.......I'm well over 30km/L at over 100kph so far). It might even work on the dragbike for a bit of extra top end charge.......... :D

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Re: Getting Better Fuel Mileage (Trucks)

Post by MadBill » Sun Apr 07, 2013 7:43 am

MODNROD, there's a wealth of Hypermiller info here: http://ecomodder.com/forum/showthread.p ... -2721.html

Also, near the end of this thread: http://www.speedtalk.com/forum/viewtopi ... 17#p426217 is a shot of the Airtabs http://www.airtab.com/ on our Vintage RR Mekur.
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