i was having this debate with some people about downshifting. What were were talking about was whether it uses extra gas or not. i am not clear on how it works with the injectors and stuff, because as a general rule of thumb, the higher the rpm,. the more gas you are using, but then again, if you are not pressing on the gas, is it not opening up as much and is it not using gas? could anyone tell me what kind/how much gas is being used when downshifting, and explain why, thanks

 

I don't know, so here's my shot in the dark. When downshifting or engine braking, there is not positive load on the engine (accelerating), so the injectors are putting in enough gas to keep the engine running at that speed. Getting something to accelerate takes a lot of energy, but to keep something moving doesn't take much, so hardly any gas is not needed when downshifting.

 

here's another shot...

supposing you had the throttle at the same position in both gears, and maintained the exact same speed in both gears.....if you were in say....3rd gear at 60mph versus 5th at 60mph, the engine has to inject gas more frequently into the chamber, because the engine is rotating faster in 3rd (even though it's the same speed on the road (60mph)).

that is why it uses more gas even though you're travelling the same speed.

[edit] - clarification


[Modified by fivespeedintegra, 10:54 PM 2/23/2003]

 

Yes, but when accelerating..say in 5th at 40mph..you need to push on the gas pedal more, then releasing more gas into the chambers. Now if you were in 3rd you dont need to push as much, sure th engine revs higher..but you put less gas in..

Honestly..im stuck on all this, as i get 160 miles per tank

 

so you have about 16mpg? I have about 20mpg and I Thought I have bad milage. someone posted recently and said they get 30mpg which sounds about right for an integra.

of course the style of driving affects mpg too

 

ttt

 

"so hardly any gas is not needed when downshifting."
-
I don't mean stray a lil bit. But when I am down shifting I hear popping sounds
from the exhaust. Don't get me wrong I like the sound, but I always wondered
if this was an indication of the motor "starving" for fuel.
I know it can possibly be valves, but I thought it might have something to do with this topic.

 

Its really something that I've never thought about but now that you bring it up.....

I still love matching revs though

 

speaking of matching revs, how many of you guys actually revmatch when you're coming to a stop, or slowing down for a freeway offramp, etc? Does it really put that much more wear on a clutch? Not sure how much this has been debated here, but what about the cost of a clutch replacement vs brake pad replacement? I have 100k on my car and still have the stock brakepads, which is probably due to my grandma-like driving style

 

i geuss i'll try to explain it if i can. if you down shift to accelerate, you will be using more gas. but if you down shift for engine breaking you wont be using much more gas. just slightly more cause the throttle will be closed. the reason for this is that when the throttle is closed, not much air gets into the cylinders. and since the computer likes an average of 14.7:1 ratio it will only squirt in a little bit of fuel. but once you hit the throttle again and more air enters each cylinder, you need more fuel to match it. and the higher the RPM you are at the more air you car will be taking in. and the more fuel you need.
so basically higher RPM means more fuel is being used to compensate.

 

I usually just throw it into neutral if I'm coming to a stop. I heard that downshifting wastes more gas too but was never sure.