Date: Sat, 24 Mar 2012 19:28:33 -0700
Reply-To: Daryl Christensen <daryl@AATRANSAXLE.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Daryl Christensen <daryl@AATRANSAXLE.COM>
Subject: Re: Fuel consumption in different gears - how does the energy /
fuel work?
In-Reply-To: <CAEuQn0bA91Gvwsf9uf+M-f=7E1zhQUi3fcrXz=9r5dm7O+1deA@mail.gmail.com>
Content-Type: text/plain; charset="US-ASCII"
I was wondering the same a while back with my Syncro Westy with a Bostig
conversion with a Turbo. That motor is a higher revving engine that likes to
run over 3000 rpm.(redline is 7200)
It has a scan gauge hooked up and you can show engine Load as one of its
many options. The load is the amount of injector on time, or fuel
consumption basically as I see it.
The efficiency of a particular motor will make a big difference. A diesel
will do better at lower rpm and mine does better at the higher rpm it seems.
On a rural road to town in 3rd gear at 40mph it says 30 load. In 4th it is
about 40 to 50 load with no boost (yet)
So at say 50 mph in 3rd gear the load says 40 or so and in 4th it says 60
or more.. With the turbo at boost, it always says about 60 to 92 (max). Full
10 lbs boost is max load and at 4 or 5 lbs it is about 60 to 70 at least.
All That tells me the engine should be working harder and getting less MPG
in the taller gears when its loaded more.
Now I may be wrong, but it kinda makes sense with this particular setup.
A stock WBX'er may be totally different in its reality.
Daryl of AA Transaxle
425-788-4070
"On the cutting edge of Old technology"
86 Syncro Westy w/Turbo Zetec in the trunk
90 Doka Tristar w/2.5 Subie
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Roland
Sent: Saturday, March 24, 2012 6:56 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Fuel consumption in different gears - how does the energy / fuel
work?
So, in driving along, with the brain wondering as usual. How much more
fuel is consumed in a lower gear vs higher gear at the same speed?
I ran a quick observation. On level ground, at 45 mph, the RPMs in 4th
gear were about 2400, and in 3rd gear it was about 3400. (These are not
absolute numbers since there are some mods on my van, and your experience
may be different).
And being a fan of physics, and mechanics, and all things we'd like to
understand better -- I was wondering, at this speed how much more fuel is
consumed in 3rd gear vs 4th gear? Now the immediate answer is none! It
takes the same energy to drive at 45 mph in 3rd or 4th. The wind
resistance is the same, the drive-line loss is the same, other friction
like tires are the same.
It seems like the ECU is most likely properly calibrated to consider
gearing (just through the senors). In 3rd gear, it would inject less fuel
per combustion, since there are more combustion events, and the required
amount for each combustion event is less. And in 4th gear, it injects more
since there are fewer combustion events per time period, and so each
combustion event is required to be stronger.
And of course the relationship is degenerative since at any speed the
engine must have a minimum amount of fuel, so this question may not apply
to really low speeds or at idle.
Again, the same energy is required to push the van at 45 mph in either 3rd
or 4th. I assume that 3rd gear will use more fuel, but why?
Thanks guys!
Roland
