Folks-
Mike Chaffee writes:
>>> First, how fast is it safe to run constantly on the highway in this car?
(Keep in mind that it's a 3-main engine and the final drive translates to
about 3700-4000 RPM at 65 MPH. I'm just wondering if anyone has any
suggestion on the upper limit to engine speed for long drives.<<<
The Paul Gilders says ...
>>> Hmm - I'm also very interested in any recommendations from the list.
My '66 Midget seems to indicate rpm of nearly 5000 at 65mph.... <<<
Then Philip J Ethier weighs in with a really good table of revs/mile with
various tires, using each of the two stock ratios.
Definitely something that gets printed out and put in my manual.
There were a _lot_ of different r.e. ratios that would fit the Spridget
axle, but my favorite was the 3.73 I got out of a 1.5 Litre Riley. The car
had an MGA-type engine and a Morris Minor rear axle (can you say "busted
halfshaft?"); the MM axle was the same as a Spridget, but narrower, I
think. That same engine/axle combination was used in other cars, notably the
Nash Metropolitan, and maybe one of them would yield a 3.73 "chunk," if you
want one. They are easy enough to change.
I found the 3.73 made my hopped-up Bugeye _much_ more relaxed on the
highway, though I never took it on any really long trips.
As for engine revs vs life, well, the racers rev the A-series engines to
9,000 these days, and get something north of 100 bhp out of them for
hundreds of miles at a time; with nearly-stock horsepower, I'd expect you
could run one at 3,500 for a _long_ time. It may be a mid-40's design, and
only 3 main bearings, but the bottom end is actually pretty strong.
Carefully built, with all the latest tricks, they are _real_ strong.
I think back when those cars were new, the standard "cruising RPM" for most
engines was reckoned as being that speed which resulted in piston
acceleration of 2,500 ft/sec/sec, or peak piston speed of 2,500 ft/sec, or
something like that. Maybe someone with an original R&T or C&D test of the
car can tell us what that speed was.
Not that it's directly revelant, but my 732i BMW turns 3000 revs at about 62
MPH, and it's gone 199,500 mostly-highway miles; the first 100,000 included
a lot of flat-out Autobahn travel.
It's not running 'em that kills 'em, it's running them low on oil, or hot,
or with the spark too far advanced, or too lean, or with the valve
clearances wrong, or with low oil pressure. If the engine is healthy, it
will make a lot of miles at any speed you can stand.
-Shel
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