Hi Frank and everyone,
Have you tried asking the software company? They might just be wrong. Sorry
Bob, I don't really follow how your argument explains why the shorter stroke
engines make more horsepower and
torque in the high RPM ranges. I'm probably missing something.
My first thought was rod angularity changes but apparently from Frank's
second post that is not the reason since the same output is given for
different rod lengths. It could be that you are coming up against
limitations in the engine's breathing. If you try different cams, heads,
headers you may find a setup which favours the longer stroke in the higher
rpms.
Still, it might just be a crap program.
cheers, derek
Derek White
37/2 Buller's Lane
Colombo 7
Sri Lanka
Tel: 94 1 581175
Cell: 94 777 475955
-----Original Message-----
From: owner-tigers@autox.team.net [mailto:owner-tigers@autox.team.net]On
Behalf Of Bob Palmer
Sent: Monday, February 03, 2003 4:58 AM
To: Frank Marrone; Tiger List (Tiger List)
Subject: RE: Desktop Dyno Fun
Frank,
Interesting question. Here's how I think it should be analyzed. To a first
approximation, engine horsepower scales as displacement times rpm. That is,
a 400 ci engine at 2,000 rpm will have about the same horsepower output as a
200 ci engine at 4,000 rpm (but half the torque of course). In your case, if
you proportion the rpm scales for relative displacement between a 306 and a
331 engine, then the two curves should be very similar if not identical. For
example, take the HP curve for the 306 engine and divide the rpm scale by
306/331 = 0.924. Then the HP peak will shift down by about 8% and of course
will fall off faster too, which matches the behavior you describe. With the
rpm scales scaled as I describe, you are comparing the engines on an equal
volumetric throughput basis, so that for equal valve sizes, volumetric
efficiencies, etc., the engines should produce equal power.
Bob
Bob Palmer
rpalmer@ucsd.edu
rpalmerbob@adelphia.net
|