Of course your tire size has an effect on it (no one today is running the
skinny things that R&T tested on them in the '60s), but my calculations
indicate 3500rpm = 61.6mph, 4000rpm = 70.4mph, 4500rpm = 79.2mph; which
makes your figures about 10mph too high all around.
My '66, which may have the wrong speedo pinion in the tranny for its
speedometer, and definitely has the wrong tranny (4-syncro, same as
yours), indicates about 60mph at 3500rpm, before I flick on the
overdrive. My rough calculations based on tire size and speedometer
charts lead me to believe my speedometer reads about 4-6% too low. This
jibes pretty well with the calculations above. BTW I got that 17.6 figure
from the 1968 Road & Track road test, which also mentions that the
original speedometer error is pretty moderate (59.4 actual at an
indicated 60mph). (They fail to mention how they got the needle to stop
bouncing long enough to get a reading).
Your numbers seem to indicate that either you have very large tires on
the car, or that you have overdrive engaged and you just don't know it. I
believe that in 1971 the overdrive was controlled by the righthand
steering column stalk, which also controls the wipers and washer. You
might try fiddling with it next time you're at speed.
Michael Torrusio had this to say:
>No, no overdrive.
>I took a ride with my GPS and got the following speeds (more or less. It's
>hard to keep one eye on the GPS, one on the tach and one on the road.)
>4th gear @ 3500rpm=70mph.
>4th gear @ 4000rpm=80mph.
>4th gear @ 4500rpm=88mph.
>Does this jibe with your experience?
>--
>Ciao.
>
>Mike.
>
>----------
>>From: Max Heim <mvheim@studiolimage.com>
>>To: "Michael Torrusio" <mtorrusi@maine.rr.com>, "MG List"
<mgs@autox.team.net>
>>Subject: Re: First hello and looking for a tonneau cover
>>Date: Mon, Feb 14, 2000, 10:40 AM
>>
>
>> 17.6mph per 1000rpm in 4th for an all-synchro B. That gives you 70-80mph,
>> roughly. Unless you have overdrive?
>>
>> Michael Torrusio had this to say:
>>
>>>Held 4 to 4,500 rpm for the entire trip, which I think put me in the
>>>80mph category. Anyone know what the revs to miles ratio is for the B?
>>
>>
>> --
>>
>> Max Heim
>> '66 MGB GHN3L76149
>> If you're near Mountain View, CA,
>> it's the red one with the silver bootlid.
>>
>
--
===============================
Max Heim
mvheim@studiolimage.com
Studio L'Image/San Francisco
415 643 9309 : 415 643 9307 fax
Studio L'Image/New York
212 242 3366 : 212 242 3399 fax
|