Bob,
OK Bob, you totally lost me with the "The area referred to is the integrated
torque over one
full cycle, i.e., two rotations of the engine. Changing rod length changes
the shape of the curve because of the different rod/crank angles, but the
integral remains constant. This neglects frictional effects, which of
course are greater with the short rods." I think you are taking/talking
about a mathematical calculation about expected torque. I don't know how to
calculate that all we had was some rudimentary data sheets in the days when
computers were fast if they were a 286 cpu.
You are about right with the repeatability of the dyno, who knows whether it
was a reasonable comparison and as far as I know I could have done something
different or the dyno could have been different as the time interval was 2
years apart as well as run with different experience and knowledge on our
part ...2 years smarter... so who knows.
As far as the RPM I am trying to guess as it was a long time ago and it
could have been peak torque at 485 ft. lbs. and peak HP may have been at
6200, obviously not exactly as stated, and as I think about it peak torque
was in fact at a lower RPM but the curve was very Flat and declining as RPM
increased. (In contrast to a very steep ramp up to peak torque) All our
files are in a box somewhere... I need to dig them out again.
As an aside our Dyno Guy was Les Davenport of the NHRA Top Fuel Crowd. The
guy is very sought after currently and I talked recently with the
Driver/Owner, Jim Epler of the Undertaker Car and he indicated to me that
the guy is one of the top crew chiefs in the NHRA (mostly he said he wished
he could afford him).
Les D. is the guy I grew up learning from...not that I am trying to bring
him down to my level as he has probably forgot more than I will ever know
about racing engines. My favourite story about him is the very first set of
cylinder heads I ported, a set of Camel back Chevy Heads, after 2 months of
grinding and polishing and making templates I take them over to him to have
them angle milled and asked what he thought. After about 40 seconds of
inspection he says "Well Tim,....You didn't screw them up!"
Anyways, He designed his own dyno and he insisted that it was 5% repeatable
but .... Who knows for sure?
Bye for now,
Tim
-----Original Message-----
From: Bob Palmer [mailto:rpalmer@ames.ucsd.edu]
Sent: Wednesday, March 29, 2000 3:08 PM
To: Ronak, TP (Timothy); jpmorrison@erols.com
Cc: 'Tiger News Group List'
Subject: RE: "Stroker" Motor
Tim,
Let's see, 485 ft-lbs @ 6200 rpm, that's 573 HP! Was this
where you got
peak torque or peak HP? (Peak HP I assume.) Was that a 350
cu in engine?
I should correct a misunderstanding regarding conclusion #5,
which I should
have anticipated. The area referred to is the integrated
torque over one
full cycle, i.e., two rotations of the engine. Changing rod
length changes
the shape of the curve because of the different rod/crank
angles, but the
integral remains constant. This neglects frictional effects,
which of
course are greater with the short rods. You talk about
running your engine
between 5,500 and 7,400 rpm and maximizing the area under
the torque curve.
I think what you need to maximize is the area under the
horsepower curve.
Dyno guys like to talk torque, but it's really horsepower
that does the
job. The concept of getting the maximum integrated effect is
important though.
I'm not sure what to make of the 1 jet size difference. What
we'd really
like to know is a comparison of the volumetric efficiency.
Generally, a
bigger jet size would suggest better breathing or longer cam
duration (but
the cam's the same in this case).
As far a scientific method, yes we'd have trouble publishing
your results
as is. One thing not to overlook is the repeatability of the
dynamometer.
This can't be taken for granted and, in fact, I understand
it's a real
important issue with professional engine builders to keep
their dyno
accurately calibrated. Of course, they need a lot better
than the ca. 8%
accuracy we're talking about in your case.
OK, back to work now!
Bob
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