[Shotimes] towing and fuel economy

[Kevin & Cheryl Airth]

Joe:
 You are correct on everything but forgot that when towing, the throttle
will be further open than when not towing. So yes the valves are open the
same amount and the rpm is the same BUT the engine will physically draw more
air. Think about the vacuum readings on your engine. At the same speed when
towing you will be running at a LOWER vacuum.
Again more load=more fuel=lower vacuum. If you hold the speed and RPM
constant.

 It has to if your fuel economy is less towing than not towing. Right??
 So the answer to your question is: The same valve lift (opening) will flow
vastly different amounts of air depending on the pressure or vacuum at or
across the valve.
 That's also why supercharger engines use mild cams. No need to hold the
valve open longer or higher because you now have pressure instead of vacuum
pushing air thru the valves.
.
.






> -- I grasp that with the trailer the engine is "working harder" and using
> more fuel.  With trailer, it takes more force to push the piston down.
The
> injectors squirt longer, yes.  The computer, aiming for stoich, keeps the
AF
> ratio as constant as possible, doesn't it?  So here is the main thing I
> don't grasp:  If the RPM is the same, then valves are opening and closing
at
> the same rates.  How does more air pass through if the valvetrain is at
the
> same RPM?
>
> Maybe I'm the slowest guy on the list.  Sorry.
>
> VO