Scott,
Absolutely correct.... 100% for the day.
Without differential calculus, it is difficult to determine piston speed at
any certain point in its travel, but a simple general equation of ("stroke in
inches" x rpm) divided by 6 will give you your average piston speed.
At one time (for a long time) 2500 fpm was considered to be an upper limit.
Even in the 60's, typical ford hipo engines ran considerably under that mark.
Add a forged crank & proper components, you can now easily push the 4000 fpm
mark. If you have cubic dollars to do the job right 5000 - 6000 should be
maintainable with todays technology.
This is why you see me doing all the hand work inside my engines to do the
lightening, balancing, polishing etc that I put into the inside of the block.
As you know, I'm an rpm freak and have to try all the hard, time consuming,
boring tricks that I can find. Best that I can do, as I dint have the tens of
thousands of dollars to give a really good race shop to build a true race
engine. (which probably wouldn't be in the true spirit of vintage racing
anyway.... easy cop out there....)
All this, considering, that at some point, you are going to outrun the flame
front which is pushing your piston. Possibly at that time reaching "less than
optimum" situation.... okay... definitely less than optimum. I dint think we
have to worry about that in our engines (unless you have a lot more money than
I think you do to develop this)...;>)
If anyone is interested in any of this, take a look at the book "Performance
Tuning in Theory and Practice" by A. Graham Bell. Excellent book. (wish I
could find my copy right now).
Getting boring now.. going to bed... must sleep....
Have a good day everyone... still have to finish my engine for VIR... maybe I
should be doing that instead of babbling...
Good night all...
Tom
#4 white
"Barr, Scott" <sbarr@mccarty-law.com> wrote:
<< You can tell that by actually measuring piston travel vs crank rotation.
It's pretty lazy up to about 90 degrees up the bore, then really speeds up. >>
Isn't this the opposite of what you'd expect? I would think that the up/down
piston travel would actually DECREASE in speed at the top and bottom of the
stroke as the rotation of the crank is more sideways (in cross-section) than up
and down. I would assume that the highest piston speed would occur where the
crank throw is at 90 degrees and 270 degrees from TDC. Am I wrong about that?
-----Original Message-----
From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net]On
Behalf Of Fubog1@aol.com
Sent: Wednesday, May 19, 2004 10:43 AM
To: charly@mitchelplumbing.com; jprice1@txcyber.com; fot@autox.team.net
Subject: Re: Crankshafts
Charly you're thinking along the right lines.... engine balancing is very
complex especially for my simple mind... but....anything you can do to reduce
reciprocating weight and/or stroke will result in much less bending loads on
shaft & by nature of doing so will also reduce couple effect. Highest load on
recip assy is on upstroke. You can tell that by actually measuring piston
travel
vs crank rotation. It's pretty lazy up to about 90 degrees up the bore, then
really speeds up. Well what speeds up must also slow down, the rest is pretty
easy to figure. Also, on the exhaust stroke, the piston isn't dampened by
combustion so it really wants to keep going up. My reasoning is to reduce the
load
because the load is going to be there, no matter what the shaft is made of or
how you strap the shaft in..
Hope this helps!
Safety FasTR,
Glen
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