David. I have a BT7 with a Lempert rear end and I have been struggling with
this same problem. I sent my speedo off to MOMA after doing all of the
recommended measurements and it came back at least 10% off. I talked to
Margaret just today and according to her they have no way to recalibrate an
odometer using RPM's. It must be revs of the cable over a measured distance.
So now my plan is to follow my wife's Camry and go 40, 50 and 60 and see
what the Healey speedo reads. On the way back from Limerock last weekend I
checked it against measured miles on the expressway. At 3000 RPM in OD I
averaged a mile in 49.6 secs. which comes out to 72.61 MPH. Unfortunately I
didn't think to check it without the OD.
The best info I have seen on this subject is at
http://www.ewilkins.com/wilko/healeygears.htm.
According to the chart at 3000 RPM you should be at 58 MPH with a factory
3.91 rear end and 64 MPH with the optional 3.55 with no OD. Cheers, JL
James Lea
2 West St. PO Box 25
Rockport Maine 04856
1952 MG TD Vintage Racer
1953 Triumph Mayflower
1958 Rover P4
1962 Austin Healey 3000 BT7
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