Does the amount of gas spent depend on the RPM that the car is running at, or the throttle? I've heard both...

 

depends on how hard you drive your car and when I mean "how hard" I mean you don't have to necessarily redline the engine but quick shift at 4-5 grand rpm(1st, 2nd, etc.) and going fast. That will definetly take some gas. Its all common sense the more you drive, the more gas it will burn. Period.

 

I think it's both. That's why on the freeway you wanna stay in 5th. I just use whatever gear I can get around best with. I'm not really that mindful of gas mileage, I redline my car at least but usually more than once whenever I take it out (3-5 days a week) and still manage naer 300 miles per full tank


Modified by alfaaay at 11:53 PM 11/16/2003

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by alfaaay &raquo;</TD></TR><TR><TD CLASS="quote">I think it's both. That's why on the freeway you wanna stay in 5th. I just use whatever gear I can get around best with. I'm not really that mindful of gas mileage, I redline my car at least but usually more than once whenever I take it out (3-5 days a week) and still manage naer 300 miles per gallon.</TD></TR></TABLE>

300 per gallon? damn

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by King_j &raquo;</TD></TR><TR><TD CLASS="quote">

300 per gallon? damn
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Damn I really wish that wasn't a typo...especially with gas prices these days!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by King_j &raquo;</TD></TR><TR><TD CLASS="quote">

300 per gallon? damn
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damn i only get 250 miles on a full tank..

 

from what i know
the higher the rpm, the more gas you use b/c with more power as you go up in rpm, the more fuel that is needed

also, this was explained before and made sence:
if you going 20 mph in 5th and trying to climb to say 40, even thought the rpm is lower, it will take more gas.
analogy-take a bike, the higher gear its in, when you first start the bike, its hard, therefore taking up more of your energy. but when you get the bike going, you want it to be in the higher gear.

makes sence?

 

The rate of fuel coming through the fuel injectors is based upon both engine speed and throttle position.

At a higher RPM obviously the injector is going to be firing more often.

Also when the throttle is opened more, the ECU tells the injectors to put in more fuel to go with the increased air from the intake.

So if you're cruising at 80+ mph in 5th, the throttle isn't open very much at all, but the injectors are firing more often. But if you accelerate from 20mph in 5th gear, the injectors don't fire as often, but they inject more fuel because you've probably got the throttle nearly wide open.

 

A usual rule of thumb is that you want most of the energy spent to propel that car (overcome wind and rolling resistance), and the least of the energy to accelerate the car. Get on the brakes and you've just converted that kinetic energy into wasteful heat.

Don't forget that combustion efficiency is also a factor here, especially while cruising. Throttled engines tend to be more efficient as the load is increased, usually showing a max near about 80 percent where combustion and pumping efficiencies overlap. This is why small engines run harder but are very efficient for a given constant speed.

To answer your question, fuel economy is dependent on both RPM and thottle position, but there may be regions of varying RPM and throttle position that may give the same efficiency. It can be very different for different engines...