John,
What you say is true, a single spring-mass system certainly does have
an harmonic frequency. As to whether IC engine speeds produce oscillation
rates at the harmonic frequency or its multiples, I don't know, and I left
my Engineering Machine Design text at home today. It's certainly possible.
Presumably one of the reasons that hot cam-valvespring kits come with
double valvesprings is that in order to increase the spring rate you must
increase spring wire diameter or decrease the number of coils. Since hot cams
usually involve higher lift,-- spring bind, or compressing the spring solid
becomes a factor. Increasing wire diameter increases binding length, and
decreasing number of coils reduces spring stability.
Later TR-6's also used double valve springs. The Triumph engineers(?) were
able to play with cam part #'s and ignition advance, as well as needle
selection, to maintain the HP even as smog restrictions became tighter and
tighter. Nowdays places just sell one 'stock' TR-6 cam grind for all years
lumped together, but it's probably just cheaper that way.
Are there any Ex-Triumph engineers on the list in 'Lurk' mode? Perhaps we
could have a good history of the changes made to the 2.5L engine?
That history of M.G. engines was very interesting to read.
Greg Meboe MEBOE@wsuvm1.csc.wsu.edu
Dept of Mechanical and Materials Engineering
Washington State University Pullman, Wash.
67 Spit-6 (Daily) 74 TR-6 (In Progress)
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