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RE: "Stroker" Motor

To: "Ronak, TP (Timothy)" <Timothy.P.Ronak@akzo-nobel.com>;,
Subject: RE: "Stroker" Motor
From: Bob Palmer <rpalmer@ames.ucsd.edu>
Date: Wed, 29 Mar 2000 14:08:09 -0800

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!


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