YACT: optimal MPG

[joe4324]

of course... all this bad news!

Perhaps, reducing vehicle weight, and engine drag (AC pump?) are really the best ways perhaps?

 

[infosponge]

That would be a GREAT learning tool if you can post results here and explain the data. Many people could see real-time data as the computer "sees" it.

 

[jagec]

Originally posted by: BDawg
Doesn't your speed play a role too? Sure, you're revving high at 5000 rpm, but if you're going 120 mph, that helps your mpg.

120mph = huge amount of wind resistance. So you have to really get on the throttle to keep that speed up.

~55 in your tallest gear (and keeping that speed CONSTANT) is usually your best mileage.

 

[KokomoGSTmp]

Well, I think people are really trying to get at with "most efficient RPM", load, and throttle is basically volumetric efficency of the engine.

Think about the reasons behind the development and usage of CVT gas-electric hybrids with very high fuel efficiency...

You have the gas engine running at pretty much a constant speed thanks to the CVT. Ideally you want that engine running at a near resonance frequency if possible for a naturally aspirated engine and since this is "ideal" we can even do away with the efficiency drop from a throttle plate. Torque for acceleration is mainly through the electric motors. All of this is increasing engine efficiency and reducing pumping loses, overfueling, severe load, etc.

So if you can reduce anything that takes away engine efficiency, it will probably increase your mpg... at least on a theoritical level. I've seen good mpg gains from the uncorking of the intake and exhaust on most "modern" cars... but for uber-computerized and factory optimized cars, there's less impact since it's fairly efficient from the factory to begin with. So I'm basically reiterating what infosponge stated. Changes to the engine's intake and exhaust do help, I've seen around 2-4mpg on my family's cars depending on modifications done. Yes, you do want to avoid open loop operation but you don't want to be at high load or rpm either for too long either during accleration.

Other reasons why manufacturers overfuel is to try to keep the catalytic converter alive in some cases. In most cases, during closed loop operation the fuel mixture is cycled from rich to lean to allow the catalytic convertors to maximize their ability to "clean" the exhaust due to the optimal operating conditions of different catalyst material. Also, in other cases it does have to do with performance and the design of the engine to prevent fuel detonation/knock.

If you could find out what the Helmholtz resonance frequency of your engine/manifold is and it is possible to find a proper tall gear to reach that rpm without having the throttle plate open too much that it uses too much fuel while maintaining good volumetric efficency and minimal pumping losses...

But in real life, it's probably just easier to drive like a grandma with all your windows closed and all accessories off. Also, a truck isn't exactly knifing through the air like a Porsche... aerodynamic forces can easily become first order on the truck at high speeds... heck for any vehicle. 50ish is probably slow enough for most trucks to not sap too much engine power from wind resistance.

Also, I think this was mentioned before but a lot of cars do have a RPM cutoff at which the engine computer will not enter closed loop operation. So if you have a car that at 75mph is over that rpm threshold, you're just running on the fuel map of the computer and mpg will get worse because of that.

 

[st3]

There are so many factors it is difficult to point out one. Case in point: the chevy silverado SS and Corvette both use a 6L v-8 that are a similar design (obviously the 'vette has higher compression, more agressive cams etc, but the displacement and the number of valves are the same). The Silverado is rated at 13/17 and the vette 18/28. 28MPG with a 6L v-8! You can see how factors like gearing, weight, aerodynamics..... are at work here.

 

[The Boston Dangler]

Originally posted by: st3
There are so many factors it is difficult to point out one. Case in point: the chevy silverado SS and Corvette both use a 6L v-8 that are a similar design (obviously the 'vette has higher compression, more agressive cams etc, but the displacement and the number of valves are the same). The Silverado is rated at 13/17 and the vette 18/28. 28MPG with a 6L v-8! You can see how factors like gearing, weight, aerodynamics..... are at work here.

Manufacturer numbers are to be taken with a grain of salt. If I had a Corvette (Z06 to be exact) I promise you I would not get the rated mpg. Partly because of my condition. You see, my right foot is made of 100% lead. Sad, I know.

 

[sonoma1993]

someone pointed out about the chevy silverado ss and corvette zo6 both using the v8 6l. Part of the diffrence in mpg is the way the engine is built too. the v8 6l in the silverado is most likely built with heavier materials to reduce stress from towing and stuff. it max rpm is probably around 5500rpm the most. while the corvette engines using lighter engine materials. try towing with that engine, it'll probably wear out alot quicker. and it can also rev alot higher, most likely max rpm is around 8000 rpm.