Umm, I suspect you are laboring under a misconception. The redline does
not indicate some sort of temperature limitation, but a mechanical
limitation; i.e. the upper limit of piston and valve speed. The valve
springs, depending on their metallurgy, are only capable of returning the
valves to the closed position at a certain speed -- above that speed the
valves will not fully seat. This is called "valve float". Under this
condition the engine ceases to produce power and valve damage begins. As
this is the limiting factor to engine RPM, usually the other
reciprocating components are not designed to exceed this limit, either.
Meaning that connecting rods or crankshafts may also fail at speeds above
redline. In actual usage, there is a safety factor built-in to the
indicated redline, but with LBC engines, there is little incentive to
test it, since the power drops off noticeably as you approach redline
(well, maybe not in a TwinCam!). The reason so many of the tachs have the
same redline marking is probably due to the fact that all of the engines
are basically similar: small displacement, pushrod, OHV inline 4s, using
similar metallurgy and asembly techniques.
Charles D. Sorkin had this to say:
>Deal List:
>
>This whole discussion makes one wonder about the meaning of the redline is,
>anyway. I assume it represented the point at which the cooling system could
>no longer dissipate heat at the rate that the engine produces it. However,
>in going through boxes and piles of used guages at different LBC events, it
>seemed that they all pretty much had the same redline at about 5500. Every
>single one had the same redline, although the tachs were allegedly for all
>sorts of different marques with widely varying engines.
>
>I now suspect that the tachometer backgrounds were all printed by the same
>printer at the same time by Smiths, and BMC just ordered them all. Thus
>regardles of where the engine should top out, all MG's seem to have about
>the same redline. (They didn't alter the tach on cars with an oil cooler,
>did they?)
>
>Regards,
>
>Charles
>'74 Midget
>cdsorkin@ix.netcom.com
>Bloomfield, NJ
>
>
--
Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the red one with the silver bootlid.
|