Maximum Piston Speed

[Kris Weldy]

Use the 350 block with the 400 crank(383 ci)-theres a low budget killer
there.---Your friend,
Kris Weldy
Arlington Texas
88supra turbo auto 9.1 1/8th
aim :volvofam3     --
yahoo:supratheonlywaytofly
www.turboboss.com
----- Original Message -----
From: "yahoo" <dhunt16 at yahoo.com>
To: <diy_efi at diy-efi.org>; <diy-turbo at yahoogroups.com>
Sent: Monday, December 17, 2001 5:59 PM
Subject: Maximum Piston Speed


>
> 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
>
>
>
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