MPG Question (point me in the right direction)

[Aloicious]

max efficiency is reached at max TORQUE, not max HORSEPOWER....that is what tempted is saying, I just wanted to clarify a little bit, because just saying 'power' can get a bit confusing.

also saying that it takes the same amout of fuel to move a vehicle at a given speed is the same with a 3 cylinder vs a v10 isn't fully accurate...it has to do with the engine's brake specific fuel consumption (BSFC), or in otherwords the amount of fuel requred to produce a certain amount of torque, or the efficiency of the engine to convert the combustion reaction to mechanical movement. if the two engines were indentically efficient, then your statement would be accurate, however, no two engines will be identical in efficiency especially with such a wide difference between them, even in the most perfect controlled enviroment that man could devise, so that statement would only be applicable to theory discussion.

 

[Tempted]

max efficiency is reached at max TORQUE, not max HORSEPOWER....that is what tempted is saying, I just wanted to clarify a little bit, because just saying 'power' can get a bit confusing.

also saying that it takes the same amout of fuel to move a vehicle at a given speed is the same with a 3 cylinder vs a v10 isn't fully accurate...it has to do with the engine's brake specific fuel consumption (BSFC), or in otherwords the amount of fuel requred to produce a certain amount of torque, or the efficiency of the engine to convert the combustion reaction to mechanical movement. if the two engines were indentically efficient, then your statement would be accurate, however, no two engines will be identical in efficiency especially with such a wide difference between them, even in the most perfect controlled enviroment that man could devise, so that statement would only be applicable to theory discussion.

I used hp because I thought Joules would be too detailed. Most of the guys here understand the term hp more than Joules. And yep, the thermal efficiency of the engine is the variable. An engine running at 25% thermal efficiency will outperform an engine at 20%, all else equal. What I was getting at is there isn't a way to significantly alter the Vortec 5.7 to achieve better economy. The best way to add some MPGs is to have the timing tuned to max ignition advance before detonation on the highest available fuel rating. If at all possible, avoid E10 with older engines. It will cause lower MPGs without exception when compared to 100% gasoline. A unit of fuel is a unit of fuel, it produces the same energy in any engine. If the fuel is being completely burned then you can't make an engine much more efficient.

 

[Aloicious]

yeah, actually all ethanol blends, E10, E85, and so on, are less energetically dense than gasoline. the flex fuel vehicles have to run larger injectors than others because it takes more volume of fuel to produce the same amount of power with E85 than straight gasonline or E10.

you can alter an engine to help, but like you said, not significantly, a couple mpgs would be somewhat realistic, but most of that comes from correcting errors or issues rather than actually improving the basal efficiency of the engine itself...though with significant mods you can alter the efficiency, but like you said, its not going to make mpg miracles...the same could be said for really any engine...

 

[Tempted]

I recall reading about a completely ceramic block but I don't remember where. Would be cool. Dissipates heat immediately and would be lighter. Plus ceramic can handle absurdly high temperatures so you probably wouldn't need much as far as cooling and oiling is concerned.

 

[DRAGGIN95]

I also had read an article about an indy car engine that someone had taken the temp down to way below zero, I don't recall the actual temp and it was getting 100 MPG, pretty interesting stuff.

 

[TylerZ281500]

thats odd

 

[DieselPower]

The 120hp engine and 300hp engine use exactly the same amount of fuel to make 60hp.

Now, that is in a perfect world. In real world our engines always produce an excess of power or do not completely burn the fuel and spit it out the exhaust. But even so it takes approximately the same amount of fuel to move a 5k lb vehicle at 60mph whether you have a 3 cylinder or V10.

True enough, the catch is that the engines are usually geared to leave some hp on the table. By that I mean that the 3 cylinder engine may make the 60 hp required @ 4000 rpm for a vehicle to maintain speed, while the V10 makes that 60 hp around 400 rpm. The problem is that the gearing makes the V10 run that speed at 1200 rpm, where you are making 3x the power that the vehicle needs to move at that speed. The extra power is available for hills and acceleration - but it's still being made and not used normally. In a more perfect world, a CVT setup would match the engine's output to it's speed requirements and net you the efficiency that your theoretical example would give.

 

[Tempted]

Yes but what I was getting at is any given engine uses the same amount of fuel to make 60hp. The variable is how much fuel is introduced into the combustion chamber that isn't used, and there is where the efficiency comes into play.

 

[Edahall]

What I was getting at is there isn't a way to significantly alter the Vortec 5.7 to achieve better economy. The best way to add some MPGs is to have the timing tuned to max ignition advance before detonation on the highest available fuel rating. If at all possible, avoid E10 with older engines. It will cause lower MPGs without exception when compared to 100% gasoline. A unit of fuel is a unit of fuel, it produces the same energy in any engine. If the fuel is being completely burned then you can't make an engine much more efficient.

How does one have the timing tuned to max ignition advance on these engines? There isn't some kind of pot switch that you can quickly do this on the fly?

Also, is the stock timing already about as good as it's going to get with low grade fuel?

 

[Tempted]

Actually the stock timing sucks. I recently learned it is set at 0 where as I have been setting it at 8* advanced forever. I'm assuming that is the reason my TBI trucks do far better than many others. The timing has to be adjusted by the computer, it isn't as easy as loosening the hold down and spinning the distributor. I have seen where people have used HEI style distributors on TBI vehicles and used a standard spring kit to adjust the timing to their liking. Apparently you have to run the tach signal from the HEI distributor to the TBI computer for the VSS to work. I haven't tried it. One thing that makes a difference is deleting the knock retardation. If the knock sensor picks anything up it will retard the timing and increase the fuel delivery, dropping the power.