As always, engines are pretty dynamic critters and making one parameter
change without optimizing for it doesn't generally do much. Like sticking a
nicely flowed intake manifold on a stock head.
Long rod engines with everything else optimized are bound to perform better
than short rods. Ricardo said that back at the turn of the century. Longer
dwell at the top and bottom of the stroke, smoother piston acceleration, and
the potential for light piston weight all favor long rods. I can't think of
a thing that's good about short rods except that the engines can be shorter.
-----Original Message-----
From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net] On Behalf
Of joe dirt
Sent: Monday, June 13, 2005 1:47 PM
To: barry rosenberg
Cc: fot@autox.team.net
Subject: RE: 225hp
It is my understanding that longer rods and shorter pistons is not what is
making the power alone, it is designing a cam to take advantage of the
greater piston dwell at tdc and other variables. So if they had put a cam in
the motor that was designed to work with that combo I'm sure it would have
made more power. I have not seen the article, so I don't know what they had
before the longer rods/shorter pistons. As Barry has made the point a
builder going from stock Triumph rods and stock sized pistons will see a
great reduction in weight than say light aftermarket stock lenght rods and
aftermarket stock sized pistons. The latter seems like the case in the Hot
Rod article. As Smokey Yunick said "Use the longest rod you can fit in a
motor." Also a forum (www.speedtalk.com) I frequent with some HUGE names in
the engine builder circles had a thread on rod ratios. They basically
resolved that it's a bunch of bs, and to follow Smokey's motto.
barry rosenberg <britcars@bellsouth.net> wrote:
I understand the new Hot Rod magazine issue has an article on longer verses
shorter rods. They built an engine and swapped rods and pistons only.
They found no power difference. I have not read it yet, but I must assume
they had the rod/piston combinations weigh the same. I use longer rods in my
TR4 motor so that I could reduce the piston size, weight, and friction. This
should provide more rear wheel horsepower. So far it seems worth it. Who
else is doing this to get rid of that huge TR4 piston? Barry
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