r u using more fuel at 3000 rpm in 4th gear at full throttle or are u using more fuel at 6200rpm in 1st gear at half throttle? asking cause i duno if the fuel consumtion is determined by the engine speed or by the throttle(cause doesnt the throttle body just open up the air flow and not the fuel line?). flamers welcome, but please provide answer..... thnx. why is this such a great site? (searched)

 

There are factors which effect fuel milage (consumption), they being:
vehicle speed
gearing
throttle position
drag (aerodynamics)
rolling resistance

I would say that both would be close, why?
WOT @ 3000rpm in 4th = greatest fuel delivery, medium rpm (half the other sample)
1/2T @ 6000rpm in first = medium fuel delivery @ high rpm (twice the other sample)

 

so does the throttle determine the amount of fuel going into the engine or does the engine speed determine the amount of fuel going into the engine?

 

Both
You've got to think of rpm as more like power strokes per minute.
all things being equal (for this discussion) assume each power stroke requires x amount of fuel
So, the more power strokes (rpm) per minute means more fuel per minute.

Throttle, by it's nature chokes the engine (reduces power) by restricting the amount of air that the engine pulls in.
Generally, the wider the throttle is opened, the more air is allowed into the engine, and with more air, more fuel is introduced to maintain the a/f ratio. So here too we see that more throttle equates to more fuel also. This holds true even if rpms do not rise sinse air flow will continue to increase right to the point where manifold pressure reaches 0.0" hg

 

(great explanation by the way) /\ okay. lets say/pretend theres no engine attached and its only the fuel rail and the throttle body, does the opening of the throttle depend on how much fuel is being mixed in?
(no ones biting in the tech forum) thnx P ur insanly knowledge about engines.

 

You have to reverse your thinking on this one.
In effect, the throttlebody is no more than a valve which regulates the amount of air which enters an engine (you'll note that no fuel lines run to the TB). It is the responsibility of the Engine Management System (using the Throtle Position Sensor, ECM and others sensors) to meter the proper amount of fuel (via injector pulse timing) to achieve the correct air/fuel ration (as sampled by the O2 sensor(s).

P

 

i think this is also going to depend on the health of the engine, and the particular computer set up being used. fuel tables are going to come into play a bit.

if i wasn't about to fall asleep, i gurantee i could provide a logical and mostly correct answer.

 

http://www.scangauge.com/

heres a sweet lil gadget that i plan on buying very soon to see at what speed gets the best mileage.

and this would give you a 100% correct answer.

 

I will await your "more correct answer".

The internal combustion engine is much like a compressor; both have intake and exhaust valves, pistons etc. And they still operate under the same principles.

In both cases, the only effect the "health of the engine" would have would be to effect how far open the throttlebody has to open (due to pumping losses) to develope the same amount of horsepower. The ratio of Air to Fuel, which the Engine Management System maintains, remains the same; between 14:1 (rich) to 16.4:1 (lean).

"Computer setup used" and fuel mapping are useful tools, when you're compensating for turbo installations (extra air intake) and such, but the internal combustion engine will run only within a very narrow A/F ratio, regardless of what widgets and bells you hang on it. In fact, up to 7psi turbo systems need nothing more than larger injectors to compensate for the additional air forced in.

 

Nice little unit if you've got the room for the display.
The Trip computer portion of it has been around since the late 70's (although not in this incarnation.) (da..m, I'm showing my age!!!)
Back then, it was a ham fisted installation involving strapping magnets to the driveshaft, mounting sensors and what felt like miles of wiring
They were no more than a toy at that time, and soon disappeared.
They can be fun to play with (however) and can teach you to be a more efficient driver.

P

 

k. i think im almost there. the throttle only constricts the airflow to the engine while the ecu reads the engine speed to determine how much fuel there is needed to be put into the valves. (so u MIGHT be better off flooring it at 1800 rpm at full throttle all the way through.)<--- auto tranny wont cut it.

 

wow, remind me to not post 3 minutes before i fall asleep

first, let's make some assumptions.

let's say, that assuming the same throttle position, the same amount of fuel is used per power cycle.

let's also assume that at half throttle, you're using exactly half that amount of fuel per power cycle.

ok, now let's assume there are no other losses.

now, i've just described a situation that's not too possible.

for this excersize, we'll use units of one, based on 1 unit of fuel per power cycle at full throttle.

that would give us 1500 units per minute at full throttle in 4th gear.

now, assuming that we're using half the amount of fuel at half throttle, we're using .5 units per power cycle. .5*3100=1550.

so, with those assumptions, you'd use more fuel at 6200RPM and half throttle.

i mentioned engine health because if you're having compression loss, you're going to have the throttle further open, and since it's further open, you'll pump more fuel.

over simplified, yes. doesn't account for any losses or strain on the engine. doesn't help that i pulled it out of my *** for the most part, either.