jaltman@altlaw.com wrote:
> Lets try this again. Would one of you 6 drivers please note
> your tach reading at 60 MPH and let me know what it is?
> Please. No OD.
Jim,
I'm sorry that I didn't reply the first time, but one of
my TR6s in in winter storage, and the other is awaiting
a new transmission.
From my recollection of many hours in the TR6, the RPMS
in 4th gear is very nearly 500rpm per 10mph. Within the
accuracy of my speedometer and tach, I would see 3000rpm
at 60mph. Actually, I seem to recall that on my car, the
tach reading is slightly more than 500rpm per 10mph in
non-OD 4th -- more like 3150rpm at 60mph.
You can also find this figure in the Bentley manual on
page 44. There is a chart for "Effective Gearing" giving
"Engine speeds (rev/min) at road speeds of 10mph and 10kmh"
It indicates 482rpm for 10mph (US-spec cars) which would
be 2892rpm at 60mph in non-OD 4th gear. The same table
also indicates 20.7mph per 1000rpm, which means 3000rpm
would be 62.1mph. This differs from what I see in either
of my TR6s.
However, the exact number is likely to vary somewhat
depending on things like what type of tires are on the car,
if the wheels are stock, and even how much air is in those
tires. So I find it quite reasonable that my empirical
numbers differ from those in the Bentley / TR6 factory manual.
If you are trying to calibrate the tach, I would suggest
instead using an external electronic tach hooked up to the
distributor to calibrate. You can do this in your garage.
If calibrating the speedo, the easiest way would be to time
yourself on an officially measured mile or quarter mile (do
you have any aircraft-enforced speed traps with quarter mile
marking on the road?) on a road near your house. Actually,
if you are good friends with a police officer, there's an
even easier way! Either of those are sure to be more accurate
than using the tach to calibrate the speedo, or vice versa.
--ken
VTR WWW Maintainer -- http://www.vtr.org
'70 & '74 TR6 Daily Drivers (well, 8 months per year...)
--
Kenneth B. Streeter | EMAIL: streeter@sanders.com
Sanders, PTP2-A001 |
PO Box 868 | Voice: (603) 885-9604
Nashua, NH 03061 | Fax: (603) 885-0631
|