Kathy and Erich Coiner wrote:
>I get 13 in my Tiger around town. I got a whopping 15 mpg on the way up to
>Mammoth last June. I have a 500 cfm Edelbrock on a 260 ........ and 3.23:1
>gears :(
>
>Erich
>
Erich,
Our Tigers are similarly equipped, almost. My 260 has the F4B and 465 CFM
Holley of the LAT combination, not a huge difference from the Edelbrock 500,
which is a good carb.
I did zero in the main jet size down two steps (.001/step at that size) as the
Edlebrock Fuel Air ratio meter said it was too rich. It is still
stochiometrically rich, but that's due to recommendations because of the lousy
gas. I did change the secondary diaphragm spring to the "plain" color, added
the Pertronix I ignition and points type ACCEL "performance" coil, and change
the distributor springs for faster advance. I do not believe these
modifications, except for the main jets, are all that significant in gas
mileage. They do help acceleration and smoothness.
What is different is that my rear axle is still the stock 2.88, giving 72 mph
at 3,000 rpm, and the Mk II transmission with wide ratio gears, giving the
acceleration performance of a numerically high rear end, without the penalty of
too high a cruising rpm. The rear end change is a common "quick fix" that has a
lot of penalties in top gear.
As a result, my around town mileage is 15-17 mpg, driven with a little
enthusiasm to help the poor middle eastern oil magnate :-( , and 18-22 on the
road at similarly excessive speeds (like the engine seems to LOVE 3,000 rpm,
the exhaust note loves it, and the sound is resonantly rich.
Anyway, this is just a note for comparison. "Your mileage may differ". "Do not
attempt this at home", "This demonstration is on a closed course by a
professional driver", and all those other BMW disclaimers. :-)
For those who would like to "dry run" their own choices of tire size, rear end
ratio, transmission gears for each gear - Bob Hokanson's Excel Calculator
(with free downloadable reader) is a great and simple to use tool. It shows you
many combinations at the same time, allows you to change the rpm, gear you are
in, and all other variables, to see the results, for 4 and 5 speed
transmissions. No fancy spreadsheet knowledge required. Dead simple.
Direct Link:
http://www.TigersUnited.com/tech_tips/HokansonGearSpeedXL/pt-HokansonGearSpeedXL.asp
Steve
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Steve Laifman
Editor
http://www.TigersUnited.com
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