Since acceleration is the name of the game (when it comes to gearing), the
first thing to decide is how close the rations are from one gear to the
next. For example my first autocross car was a 72 Pinto with a 2.0 and 4
speed. First then second were good but from second to third was a "large"
gap. I replaced this with a transmission from a Cortina which had a close
ratio between each gear 'except' third to fourth. This gave me three VERY
usable gears. At this point IMO you choose a gear that will achieve your
determined maximum speed at a solo, taking into consideration tire size, in
third gear at 90%-95% of top "usable" rpm. This allows for the slightly
faster courses, and gives you the gears you need during the courses, and
from the start line.
In the case of my last project car (an Opel GT with a 13b automatic) we
determined to do about 80 in 2nd gear we could use a 5.3:1 ratio. This
would have been much better for the starts than the 3.4:1 that was/is in the
car. Of course being in MOD makes it easier to put in what you want. Since
I don't know what it is you are changing be sure the rules allow whatever
change you want to make first. Your fellow competitors WILL know if you
shift too soon and often on the same course they are running.
in HIS grace thru Jesus,
Don
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