[AT] tractor fuel efficiency

Wed May 10 17:46:06 PDT 2006

Generally running engines at lower speeds improves fuel economy for two  
reasons.  The engines internal friction goes down when you reduce speed so  you 
burn less fuel just to turn the engine over.  Second if you run in  higher gears 
but lower engine speed the load goes up and you need to open the  throttle.  
This reduces the manifold vacuum and the pistons don't have to  work against a 
high vacuum on the inlet stroke so the engine is more  efficient.  More fuel 
is burned each piston stroke, but there are less  strokes so you win.  The 
same things apply to cars - which is why running  in higher gears or overdrive is 
generally better or with a smaller engine  working harder.

Diesels (with few exceptions) never have inlet throttle plates so the  
pistons never work against a vacuum -  this is one of the reasons diesels  are far 
more efficient than gas engines at lighter loads.  

I doubt if advancing timing over specifications will help much for either  
diesel or gas.  Perhaps 1 to 3 percent.  Biggest risk on gas would be  damage 
due to knock.  With diesel the loads on the crank and head gaskets  will go up 
due to higher pressures.  I usually run gas engines 1-2 degrees  advanced - its 
probably more of a "feel good" thing than a big savings.

Bob Straub
Farmall M-200-F12- (and diesel F-20 conversion  project)

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<DIV>Generally running engines at lower speeds improves fuel economy for two=
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reasons.  The engines internal friction goes down when you reduce speed=
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you burn less fuel just to turn the engine over.  Second if you ru=
n in=20
higher gears but lower engine speed the load goes up and you need to open th=
e=20
throttle.  This reduces the manifold vacuum and the pistons don't have=20=
to=20
work against a high vacuum on the inlet stroke so the engine is more=20
efficient.  More fuel is burned each piston stroke, but there are less=20
strokes so you win.  The same things apply to cars - which is why runni=
ng=20
in higher gears or overdrive is generally better or with a smaller engine=20
working harder.</DIV>
<DIV> </DIV>
<DIV>Diesels (with few exceptions) never have inlet throttle plates so the=20
pistons never work against a vacuum -  this is one of the reasons diese=
ls=20
are far more efficient than gas engines at lighter loads.  </DIV>
<DIV> </DIV>
<DIV>I doubt if advancing timing over specifications will help much for eith=
er=20
diesel or gas.  Perhaps 1 to 3 percent.  Biggest risk on gas would=
 be=20
damage due to knock.  With diesel the loads on the crank and head gaske=
ts=20
will go up due to higher pressures.  I usually run gas engines 1-2 degr=
ees=20
advanced - its probably more of a "feel good" thing than a big savings.</DIV=
>
<DIV> </DIV>
<DIV>Bob Straub</DIV>
<DIV>Farmall M-200-F12- (and diesel F-20 conversion=20
project)</DIV></FONT></BODY></HTML>