[Land-speed] Enine Torque Theoretical Question...

[Ed Weldon]

OK Mayf.  I'm going to go back and dig out Obert's book (published when I
was 5) and visit with him for a while.

Sometime later -- This is hard to do in a short burst but I'll try......
At all speeds within the mechanical limits of an engine (of known constant
displacement) the torque would stay the same if:
1. Volumetric efficiency stays at 100%
2. Mechanical efficiency stays at 100% ( zero friction, pumping losses and
accessory drag)
3. Throttle setting stays the same.
4. Ignition and burning of the fuel stays the same if not perfect. (did I
forget anything here)
Trouble is that the volumetric efficiency drops both below and above the
design speed range of otto and diesel cycle engines largely due to the way
valves are timed.  This means less fuel/oxidizer gets efficiently burned at
each ignition stroke.
To make it worse the mechanical losses tend to go up mostly exponentially
with speed.  This especially includes piston/ring/bearing drag and pumping
losses moving intake and exhaust gasses.
You can play some tricks to flatten out the torque curve and push its drop
off higher in the RPM scale.   Variable valve timing is one obvious way.
Another is to reduce friction losses with better lubrication and more
accurately built engine mechanisms.  And then you can bring in some of the
oxygen in liquid form rather than a gas like air.  This effectively improves
volumetric efficiency and reduces pumping losses on the intake cycle.  (i.e.
nitromethane)
But there is no way to completely defeat the friction and pumping effects.
So the net useful energy you get out of each power stroke (which determines
torque) will eventually drop off with increasing RPM's.
BTW, your observation about supercharged engines can probably be explained
as a coincidental effect of the greatly increased pumping losses in the
blower engine itself.
I'd also reiterate that the torque/speed characteristics we observe have a
lot to do with the job our race motors were originally designed for and the
mods we put into them.
Ed Weldon

----- Original Message ----- 
From: "drmayf" <drmayf at mayfco.com>
To: "LSR" <land-speed at autox.team.net>
Sent: Tuesday, April 29, 2008 11:50 AM
Subject: [Land-speed] Enine Torque Theoretical Question...


> Well, shoot. This did not generate as much discussion as I hoped it
> would.