An enthusiast's guide to saving fuel (Road & Track article)

[DAN]

found it. pg 105, road and track may 2006. what surprised me was how much opening the throttle as wide as possible and holding down revs saved gas. i knew it did but %20! se aso pg 122, tech tidbites and the hybrids tests.

[SVOboy]

Here is a link to the actual article for those interested in reading it: http://www.roadandtrack.com/article....rticle_id=3424

[DAN]

see also pg 122, tech tidbites and the hybrids tests.

[MetroMPG]

I'd seen this article before. It contains some good info & and a lot of really misleading & confused info.

Comments...

• I'd forgotten that they actually quantified the vehicle weight when talking about the "carrying additional weight penalty". Even the oft quoted EPA stat doesn't put it in context
  

  "Add 100 lb. to a 3000-lb. package, and this 3-percent increase in load invokes at most a 1.5-percent penalty at the fuel pump."

• On the subject of WOT/short shifting, they are somewhat misleading.
  .
  • First off, full WOT will retard ignition timing and enrich the fuel mixture - there goes your efficiency gain from reduced throttle losses!
  • Second, if you use this accel technique, you must not brake after accelerating. The penalty of converting kinetic energy into heat & brake dust after a vigorous near-WOT/short shifting acceleration is massive compared to doing the same after a theoretically inefficient feather-footed acceleration.
  • Third, if your target speed is high and you'll be cruising at it for some time, it is not as efficient to near-WOT/short shift to get there. Try it, with instrumentation, and see.
  • Near WOT/short shifting to reach some target speed works best when it's done during P&G, or if EOC follows.

• It suggests shutting off the engine isn't worth it "Unless the stop is prolonged (a railway crossing, for instance)". Perhaps true in a large, old, cold, out of tune engine that doesn't start up easily, but we know it saves fuel in a small, warm, fuel injected engine that restarts well - even if the stop is very short.

• The article confuses coasting in gear for fuel-cut with coasting in neutral, no fuel cut.

• And it is flat out WRONG in this statement:

  "Plus, of course, hybrids should never be coasted. Out of gear, they're giving away all of their coast-down regen."

  Coasting to a stop is hugely more efficient than using any form of braking, including regen in a hybrid.

There are some nuggets in there, but generally, I'd say: reader beware!

[Daox]

Originally Posted by MetroMPG

There are some nuggets in there, but generally, I'd say: reader beware.

I entirely agree. They are intended to be good (and are for the most part), but they obviously don't know their stuff really well. Of course, then you get people that trust the article and take it as written law. Think Art Spinella.

I know I always try to take everything with a grain of salt and always question 'why?', or 'does that make sense?' when I read things. It really keeps your eyes open and its amazing what you'll find. Us enthusiasts are usually way more knowledgable about things than the average journalist. Heck, a lot of us know more about our own cars than the mechanics that work on them too.

[8307c4]

This WOT acceleration concept is a load of crap, but just as soon as someone first pays me the $100 it takes to fill the tank in my truck, then hand over another few thousand to compensate for all the extra wear and tear and be ready to spring for new tires or anything else that should break or wear prematurely and I'll gladly WOT accelerate any time anybody would like me to.

Because that's a LOT of wear and tear on my vehicle, I might get better mileage maybe but with a 300hp engine that can suck fuel like the space shuttle on take off I doubt it. What I do know is I can watch the fuel gauge move under WOT acceleration on a 30 gallon tank and the rear tires wear a LOT faster on hard acceleration and we're talking 1-200 dollars each for these, then that's just for starters.

The transmission develops shavings in the pan, watching these between fluid and filter changes is critical to maintaining transmission longevity. So long there is only a minor amount that should be fine (minor = none or almost none), but anything beyond that can mean only that the bands and possibly other components are wearing far beyond the norm, a rebuilt 4-speed O/D for my vehicle is like 4-5 maybe 6 thousand dollars so better make sure someone's got plenty of spare cash to pay me for this.

Odd, why I don't see any spare cash volunteers jumping at this opportunity now?

The engine, too, many components will never last nowhere near as long if driven aggressively. The torques exercised upon internal and external parts are so extreme that any vehicle that is always driven in this fashion wears parts something like 8-10 times faster when compared to a vehicle that is driven in a civilized manner.

We're talking the engine and transmission rubber mounts that hold these to the frame bend under load, so in addition to the components and everything I can assure you the wear and tear that results from driving a vehicle in this fashion quickly costs way more than the puny amount of fuel it might have saved.

There's absolutely no way in hell one can save money by splurging, come on.

Nice and easy driving does it, that's the best way, it's the only way.

[Daox]

I won't pay for your gas just to prove something thats already been proven many times over. However, I will explain it to you. WOT (actually, as much throttle as you can get without going into closed loop mode) combined with short shifting is where you see the gains. High engine load with low rpm is what gives you the best efficiency. This is how the MPG challenge racers do it. Even with your 300hp engine, your not putting out massive horsepower at 1500 rpm, so your not going to break your tires loose. If you are spinning your tires at that rpm/load you engine is way too powerful for your car. Also, wear isn't a big deal as torque will also be low at real low rpms. Combine that with low piston speeds due to low rpm and you actually have less wear on components.

Now, there is one shortfall and that is that you can't do it with an automatic transmission since you can't combine WOT with short shifting. In this case you have to make due using fake or false shifting technique.

Nice and easy driving does it, that's the best way, it's the only way.

Tell that to the guys getting 10+mpg over EPA's highway estimates using P&G.