Yes, that's what I understand about needing more ring gap on the
hypereutectic piston. I don't know if it is true, but I hear because they
are high silicon castings they aren't as strong as forged pistons and are
more subject to failure due to detonation because the material is harder and
more brittle than forged pistons. On the upside, they can run much closer
"cylinder to wall clearance" because piston heat expansion is less with the
hypereutectic material, thereby rings last longer but need more end gap
because the rings see more heat.
Does this correlate with what you know about hyperutectic pistons?
----- Original Message -----
From: "Larry Dent" <lwdent@fwi.com>
To: "Carl Braun" <clbraun@mwci.net>
Cc: "Kansa, Robert" <KansaR@diebold.com>; <team-thicko@autox.team.net>;
"VintageRaceNet" <vintage-race@autox.team.net>
Sent: Friday, November 07, 2003 9:02 AM
Subject: Re: Venolia Piston Failure at Mid Ohio
> The new high eutectic (spell ?) low expansion pistons require a HUGE end
> gap on the top piston ring. a 4 inch piston in a 289 requires almost
> .040 gap because the piston reflects so much more heat down into the top
> ring that the expansion is huge. We used to gap those rings at more
> than half that figure with forged pistons.
>
> I am building an extra engine for my GT 40 right now and I was
> astonished at the gap I had to run in Keith Black pistons, but just on
> the top ring.
>
> Larry Dent
>
> PS. To add one more comment on the question about horse power in the
> old twin cams. I ran an HRE (Gus Hutchenson out of Texas) 1300 cc twin
> cam in my Lotus 23 back in 1969 to 72. That engine was very exotic with
> titanium valves and other pieces made of un-obtanium and it made 155HP
> at 11,500 RPM. We were all sworn to silence on that high RPM as Gus did
> not want anyone knowing what he did or how he did it. I once missed a
> shift and put the tell tale to around 12,500 and when I called Gus he
> said "don't worry, the engine is safe to 13,000 on a momentary basis".
> That was in 1969 folks.
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