Long stroke engines have high torque for an obvious reason--the length of
the lever arm (the distance of the rod centerline from the crank
centerline). You can visualize how all this stuff works--low overlap cams
keep the mixture from getting away and give a longer percentage of the
stroke for compression. Then the exhaust valve opens late so the combustion
gasses push on the piston longer. At higher RPMs all these factors start
working against you--the intake isn't open long enough for the mixture to
get in, inertia of the mixture is working against you, the exhaust valve
isn't open long enough to clear the cylinder. Overlap becomes necessary and
the long stroke is mostly wasted because you're stroking against open
valves.
-----Original Message-----
From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net] On Behalf
Of riverside
Sent: Thursday, May 20, 2004 11:58 AM
To: fot
Subject: cranks
Recent Road and Track reviewed a book on the i believe year 2k Ferrari
F1 team. Quoted stroke on the F1 engine as something like 42mm.
Doesn't take a very long rod to get a favorable ratio. Anybody know how
long the rods in that motor are?
My 259 cid Stude V8's ratio is about 2.1:1 which is pretty good for a
"modern" pushrod V8. It has a very flat torque curve. The old Stude
President straight 8 used in their Indy 500 cars and the old Healey 100-4
both had long stroke and long rods and the bottom end torque on both of them
is really strong. Always been curious how intake valve closing timing and
R/S ration play off each other in producing torque. Drove a nice street TR4
yesterday with a fresh stock motor and got reminded how these things can
melt a set of rear tires.
art d
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