Sandro Menzel writes >
>On my '66 Midget, my calculations had me going 15 + the tach's value
>when in fourth gear. So, traveling at 5000 rpm = 65 mph, give or take a
>couple mph.
Ok, the stock tires for a '66 Midget are 145-80-13. The axle ratio is
4.22/1 and fourth gear is straight through. Plugging these facts into my
BFG-derived spreadsheet, I find the the road speed at 5000 rpm is 78.05
mph. If the tach and speedo are working, this relationship between them
will remain constant regardless of the tires you are using. Only the
actual road speed will change.
For 5000 rpm = 65 mph (actual), the axle ratio would have to be 5.07/1.
>Perhaps my tach is out of whack.
Or your speedo. Did you notice you were passing a lot of cars?
Seriously, the tach on my Midget was wildly optimistic, but yours
apparently has it beat. The speedo was fairly close at 60, according to
the stop watch and highway mile markers. I counted the turns on my diff,
and it was definitely a 4.22/1, even though the tach suggested it was a
4.55/1 unit.
I used to impress passengers by shifting WAY into the redline on the
Midget. I won't be doing that with the Europa. The converted Smiths tach
is reputed to be very accurate, and I cannot afford to blow this engine.
I have been told you can't blow the bottom end of a healthy 1275 with
stock-size valves. I don't believe that to be true of a stock
Lotus/Renault 1565 with a side-draft and a header, so I'm sticking pretty
close to the 6500 redline.
Phil Ethier, THE RIGHT LINE, 672 Orleans St, Saint Paul, MN 55107-2676 USA
h (612) 224-3105 w (612) 266-6244 phile@stpaul.gov
"Been there, done that, couldn't afford the T-shirt" - Sue Ethier
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