fuel economy

hey all, i was wondering, would changing gears while the revs r lower
decrease the amount of petrol your using? when im low on fuel im already in
5th gear when im going 60km/h.

any advice and help?

Sandro

 

thats like what... 40mph? thatll waste more gas IMO. ive tested this theory
on my daewoo(2000 lanos S) and my CRX (87 HF). running the engine in 5th at
speeds that low puts more stress on the engine (it must work that much
harder to accellerate in 5th as opposed to 4th or 3rd), thus resulting in
more fuel wasted. i usually shift into 2nd at about 20, 3rd at about 40, and
4th at about 60. 5th comes at about 65 or so, depending on my mood... this
is in MPH btw. in both my cars, ive made the trip to san antonio (about 90
miles from austin) with only 1/8th of the tank gone (gettin about 50mpg on
the highway in both cars.. more in the daewoo at times). i make this trip
weekly and have been doing so for quite some time, so ive had plenty of time
to run many theory tests. HTH!


-agent smith

 

How much more fuel economy do you see by this infintesimal change, in
comparision to a 90 mile highway trip?

 

It should increase your mileage, so long as when you shift to a higher gear
you are not opening the throttle more than you were in the lower gear in
order to maintain the same speed. Also, avoid lugging the engine, as this
will put tons of stress on your bearings and significantly decrease the life
of the engine if done frequently. These torqueless wonders need to be
shifted at a reasonably high RPM in order to not lug them (unless you are
accelerating at a crawl... which is how you'll get the best mileage,
actually). That is the nature of an engine with no torque to speak of.

Cory

 

Very true, if you drive a roller bearing Porsche from the 50's.

 

Sandro,
Since you are worried about petrol--I suggest that you buy a Civic
Hybrid--you would really enjoy watching the fancy instruments that allow
you to keep track of your petrol per gallon.

If you plan to keep your present vehicle, I advise you to check your
petrol miles per gallon while driving one fashion over a road that that
you travel on a regular basis. During the following week or month, test
your petrol miles per gallon by driving a different fashion over that same
road. Eventually, you will figure out the best way to save petrol.

 

There is no sense putting the engine in an RPM that has too low of a torque
to move the vehicle. You will end up using more gas.

Note the curves on the graph that shows the amount of torque output per RPM
of the engine. The torque is what you need.
http://dynoperformance.com/about.php

 

at what rpm should i change gears? at 3000rpm? or 4000rpm? what i ideal? is
it bad to keep changing at rpm which are too high? such as 5000rpm??

 

is it bad to keep changing at rpm which are too high? such as 5000rpm??

 

Too high RPM is generally defined as above the 'redline' for a particular
engine. That is to say, the max RPM that you are assured the parts in your
engine will hold up to. I seriously doubt any Honda 4 banger has a redline
below 5000 RPM.

For best fuel mileage you should rpobably shift around 2,000 RPM (with a 4
banger anyway), for best performance you should probably shift at or
somewhat below redline. Where you shift when desiring max performance
depends on where your engine's power peaks. If it runs out of breath at 6000
RPM then shift there, but if it makes good power all the way up to a 7500
RPM redline shift at 7500 RPM.

Cory