Maximum Piston Speed

[yahoo]

Maybe someone can help.  I'm looking at turbocharging a small block
Chevrolet.  The problem is which block do I use?  I considered using a 400
cu. in. small block, but am having second thoughts.  The 400 cu. in. has a
3.75" stroke and the 350 has a 3.5" (more or less) stroke.  I had planed to
limit RPM to about 6500 RPM.  But now I'm wondering if that number isn't
very much too high for the 400 small block with a turbo.

I've tried to find some material on piston ring sealing, as I think that is
the primary problem with high piston speed on US designed engines.  As it
turns out the maximum piston speed is at the same point that maximum torque
is being transferred to the crankshaft.  Since I'm interested in stroker
engines that will have 100,000 mile lifetimes, I think that piston speed is
a particular problem.  For example, a 3.5" stroke engine that has been
stroked to 3.75" has a maximum piston speed increase of 7%.  All other
things being equal that is a HUGE increase.

However the moment of inertia for the engine has been increased by the
square of the ratios (3.75^/3.5^2) which is 13%.  Actually, there should be
more metal in the larger crankshaft since there is less overlap from main
journal to rod journal which exacerbates the moment of inertia effect.  It
seems that with a high ratio rearend (so that the primary load at high
transmission ratios is engine inertia) will be adversely affected.  In my
case, I'm more interested in a stump puller (boat actually) and would
consider the high ratio first gear a pain in the !@#$ most of the time, but
need it when pulling up the boat ramp.  Since I'm not a racer, I don't
consider this important, but included it in the discussion for the sake of
completeness.

Here's the question.  Under high loads (turbocharged) what are the maximum
piston speeds that are associated with long life?

Is there a need to provide extra fuel when under high load to 'save' the
rings?  Maybe the real question is whether detonation is the only effect of
high power that kills the rings?

Does a long rod help with piston skirt wear?  Do they hurt? Is the offset
different with a long rod piston or does all pistons assume the 5.7" rod and
ignore the long term effects?

I've heard that all pistons for 6" rods are built with NO offset because
most folks don't want the performance hit, and don't care about longevity.
I'm considering using a long rod and a 400 cu. in. piston with big pocket
heads (and a thick head gasket) to attain the piston offset.  The target
compression ratio is 8.0:1

Are there bigger fish to fry?  That is - ring speed the least of my trouble?
I once heard that because of gas action behind the ring, the ring actually
seals better under higher load.  Does anyone know with certainty?

Can I save the rings on a stroker by giving more fuel?

dh



_________________________________________________________
Do You Yahoo!?
Get your free @yahoo.com address at http://mail.yahoo.com

----- End of forwarded message from owner-diy_efi at diy-efi.org -----
----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org