Fuel mileage

["Robin Giesbrecht" <robings@xxxxxxxxxxx>]

I understand what you are saying and maybe I  jumped the gun. Your reasoning 
is sound and I have no problem following it. All I am saying is that at a 
given rpm(up on the torque curve) and load
the 440 will run at its finest taking all items you have mentioned into 
consideration. And this will not necessarily be at a slower highway speed or 
engine speed. The vacuum gauge can be used to fine tune the throttle opening 
particularly during cruise. It is not the be all and end all but the 
internal combustion engine is a very complex beast and one could spend one's 
life trying to reinvent the wheel. I get to a point where if it makes power 
enough to satisfy me and fuel burn is acceptable then all is good. I have 
too many other things to do. But I do know one thing. The 30 some mile grade 
out of this valley to the summit of the pass is most efficiently carried out 
at around 80mph in high gear. If I slow down she starts to lug and I just 
have to push my foot deeper.Less vacuum, more fuel flow and end results are 
not worth it. Faster and I am also starting to push deep into the carpet. 
Same scenario.There is another steep long grade further down the road that I 
have to begin from almost a standing start and once I get past 70mph in high 
gear the engine almost transforms. If I had a tach I could verify I am 
hitting the peak torque curve. Talking about lower engine speeds and lugging 
my dad was/is a huge Mack man. I remember when Mack came out with the 
Maxidyne engine/transmission which pretty much revolutionized the heavy 
truck industry.They came out with a smaller inline turbo six with a flat 
torque curve from 1200-2100 rpm and a huge(as in large size) five speed 
transmission to handle the torque. This was when the standard heavy rig had 
a power curve from 1800-2100 rpm and at least a 10 speed. And everyone 
thought that peak horsepower was most important. The little Mack had 235 HP 
but would pull or outpull 350 hp Cummins and Detroits.I was a kid then but 
still remember the "races" they would have and the betting that went on as 
the Mack dealers went out to prove their point. Lots of red faces.Now flat 
torque curve engines are standard. I would think that for pulling trailers a 
tach would be a helpful instrument as you could try and keep the engine high 
on it's torque curve.

Robin Giesbrecht

>From: dardal@xxxxxxxxxxxxxxx
>Reply-To: mailing-list@xxxxxxxxxxxxxxxx
>To: mailing-list@xxxxxxxxxxxxxxxx, Robin Giesbrecht <robings@xxxxxxxxxxx>
>CC: mailing-list@xxxxxxxxxxxxxxxx
>Subject: Re: IML: Fuel mileage
>Date: Mon, 24 May 2004 11:50:04 -0500
>
>Robin, I do not fully follow your question.  Lets first repeat the subject 
>we
>are trying to answer:  For a given loading, what is better, higher rpm and
>lower load (i.e., more vacuum) or lower rpm and higher load (less vacuum).  
>The
>answer to this is as follows.  Assuming the load is not high enough that 
>you
>are in the fuel enrichment area for knock suppression, the higher load 
>(less
>vacuum) is more efficient (also, the lower rpm means less engine friction).
>The reason why the lower vacuum increases efficiency was explained earlier.
>Now, if you include the fuel enrichment part, its hard to tell for sure 
>which
>operating condition is more efficient.  The converter slippage adds another
>variable.
>
>Quoting Robin Giesbrecht <robings@xxxxxxxxxxx>:
> > it is quite simple. More air flow equals more fuel flow and less
> > vacuum.Simple. High vacuum equals less air flow equals less fuel flow.
>
>That is true assuming we are at the same rpm.  Remember, the high vacuum
>scenario is actually at a higher rpm.  Remember, the two operating 
>conditions
>we are comparing have to have the same power delivery, so the lower 
>load/higher
>vacuum case is at higher rpm.
>
>On further analysis of your statement, remember, we are talking about 
>efficiency
>here.  Efficiency is defined engine power per flow rate of fuel.  Closing 
>the
>throttle for a given rpm reduces fuel flow, but also reduces power.  As a
>result, at very low loads, the efficiency decreases.  At the extreme, at 
>idle,
>the efficiency of the engine is zero, because there is no useful work
>produced.
>
>D^2
>
>