Dave, we're talking about one of the all-time Masters of Bonneville
here, the record book is full of Lattin-Gillette team Ardun records.
As to the con-rod breakage risk, that is a fact, not a theory nor an
opinion. We're talking about a situation where the conrods are running
right at their limit of ability to hang onto the pistons and not break
under the small ends. The stress on them is close to the snapping point
due to the rpm, piston speed and piston weight. If the throttle is
snapped shut, the gas pressure over them which has been partially
offsetting the inertia load, partially balancing it if you will, is
suddenly cut off so this represents the instant of maximum stress on the
rods. Elmo told me they'd had it happen, just like that.
For many years I followed the British road-racing motorcycle sport very
closely, in the golden age of high-performance singles. They were
developed right to the limit of reliability with endurance. Numerous
experts mentioned in articles that con-rods were most likely to break
when snapping the throttle shut on the over-run. The great bike and car
World Champion John Surtees mentioned this himself in one of his books.
For years at the start of his career, he built his own racing equipment
in his garden shed.
Let me quote from Surtees, for everybody's enjoyment: "It is when you
ease the throttle at really high revs - say, for a fast curve - that a
connecting rod is most likely to go. Inertia loading on the rod goes up
as the square of the engine speed but so long as you are on full
throttle there is some gas pressure above the piston to offset part of
the upward load. When you ease the throttle you ease the gas pressure -
and that is when you should be ready to whip out the clutch like greased
lightning at th first sign of a locked engine." ("John Surtees on
Racing" London, Iliffe and Sons Ltd. 1960. P. 39).
The sports cars to which you allude, true, they constantly snap the
throttle open and shut as a part of driving and braking technique.
First, they have the finest con-rods available, second I daresay they
don't constantly have their engine at the red-line on the over-run. Or
do they?
Keep in mind, Elmo never used anything but original Ford stock rods by
preference and to keep costs down, and they're no Carrillos. You have
to look after them.
Elmo told me they like a high-gear only push start at Bonneville,
pushing with the truck up to a speed fast enough for the car to chug
away in top gear, because it's easier for the driver. I'm quite sure
that a standard part of the shut-down is to shut the fuel cut-off on the
injection at the same time you start to throttle back, to avoid danger
of hydraulicing. Cheers Bill
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