Date: Sun, 25 Mar 2012 14:58:13 -0700
Reply-To: Roland <syncronicity1@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Roland <syncronicity1@GMAIL.COM>
Subject: Re: Fuel consumption in different gears - how does the energy /
fuel work?
In-Reply-To: <4f6ef2ab.8ad6e00a.7676.5742@mx.google.com>
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Thanks all for the discussion. (this is an '89 2.1 WBX by the way)
I don't understand all of the responses, for example I am not sure what
torque has to do with my question. Sure there are some torque differences
in 3rd vs 4th gear, I can't understand how that might affect fuel
consumption.
But what David wrote makes good sense. In 3rd gear there would be more
losses in the engine itself (piston / conn rod weight reversal, valve
springs, compression events, oil/water pump). So that suggests that the
MPG would be lower while driving in 3rd gear.
But then as a counter argument (if I read it correctly), the engine might
run more efficiently at higher RPMs, at 3400 in 3rd vs 2400 in 4th.
I think we need to find some graphs of fuel consumption vs engine speed.
Ideally they would be for the WBX, but perhaps all engines have similar
characteristics. About 5 different plots, from 1000 RPM to 5000 RPM with
each plot being a different load on the engine. I think this is what I am
searching for / asking about. It is almost like reverse engineering the
ECU.
Roland
On Sun, Mar 25, 2012 at 3:25 AM, David Beierl <dbeierl@attglobal.net> wrote:
> At 09:56 PM 3/24/2012, Roland wrote:
>
>> 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.
>>
>
> But it takes more energy to run the engine faster. The inertial losses
> from reversing the pistons' direction of travel, the frictional losses from
> scrubbing the piston rings up and down in their bores, the energy lost by
> compressing the fuel/air charge and operating the valve train, the
> additional output of the water and oil pumps - these parasitic losses all
> increase more-or-less linearly with increasing rpm.
>
> It would be interesting for someone with an OBDII engine to do some
> calculations of no-load operation at various rpm, using the rpm and engine
> load numbers to determine the relative amount of fuel required to merely
> spin the engine at those rpm. I wish I'd done it while I still had my
> Honda.
>
> Yours,
> David
>
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