Ok everyone,
In plain English.....I am interested in knowing if the extra friction,
stroke and cubes generated by the stroked motor outweighs the advantage of
having a longer rod with a shorter stroke and less cubes and less frictional
heat for RPM potential. It would seem that the question is what RPM do you
want to use. Personally I would like the engine to go to 6500 RPM reliably
with peak HP at 5500-5900 and a flat torque curve with a Peak in the 4500
RPM range. I am leaning towards the stroker but I am curious if there are
any heat or tune-ability issues that result from such a low rod stroke
ratio?
Has any one got one in their Tiger and is happy with the stock cooling
arrangement. I am not going to cut up my car to put more power to it.
Regards,
Tim
-----Original Message-----
From: Bob Palmer [mailto:rpalmer@ames.ucsd.edu]
Sent: Thursday, March 30, 2000 12:09 PM
To: Theo Smit; 'Steve Laifman'
Cc: Ronak, Timothy P; jpmorrison@erols.com
Subject: RE: "Stroker" Motor
Theo, Steve, Tim,
Well, Steve did say "The 33,000, as you know, is just to
adjust for
all the measurement units." , but he didn't say just what
those units
were. Seems to be problem NASA has been having recently too.
Also, could be
the pi he's using is circumference divided by radius instead
of diameter.
Anyway, we'll let Steve report the error to the List in his
own inimitable
way. ;-)
I apologize to Tim for getting too far astray in the thread.
Seems Dick was
annoyed as well. I sure wouldn't want to be accused of
dragging reluctant
technophobes kicking and screaming into the 21st century.
Actually, I'm not
really sure where the confusion is. If it's the torque over
the whole cycle
thing, that's really not so complicated. The hot gas pushes
on the piston,
which pushes on the connecting rod, which pushes on the rod
journal. The
tangential component of this force times the distance to the
center of
rotation of the crankshaft is the instantaneous applied
torque. The
instantaneous torque varies greatly, depending on the gas
pressure and
rod/crank angle over the full engine cycle. The torque
measured at the
output of the crankshaft is the average of the eight
cylinders. A fairly
simple model that would easily run on a i286 machine shows
that the average
torque does not depend on the rod/stroke ratio, although the
instantaneous
variation does change quite a bit. (Did someone say this was
simple??)
Regarding another comment you made Tim, I'm not sure if you
meant it this
way, but I thought you might have implied that reducing the
piston weight
might result in more power. I don't believe this is so,
except insofar as
it would let you run to higher rpm before something breaks.
I think there
are some who think that the energy starting and stopping the
piston every
rotation is wasted energy, but it is actually conserved and
just adds to
the reciprocating mass of the engine. Of course, high
reciprocating mass
makes the engine respond slower, but doesn't really change
its steady-state
torque or power output.
Well, TTFN guys,
Bob
At 11:12 AM 3/30/00 -0700, Theo Smit wrote:
>Sounds good, but I think you're out by a factor of 2.
>
>AFAIK, HP = torque * RPM / 5252.
>But 5252 * pi = 16500 (more or less)
>
>Theo
|