Benjamin Ruset wrote:
>
> >I'm on my 7th and 8th MGs (52 TD and 68 B) and seek advice on the MGB:
> >(1) Is there a simple retrofit 5 speed transmission ?
Simplest and cheapest is an overdrive on B's.
> I have heard that there is a conversion for a Datsun 5 speed out there. I'd
> be interested in this as well.
That's for 1275 (pre-75) Midgets.
> someone told me once that the gearing for 4th in a 4 speed was the same as
> 5th on a 5 speed. is this true?
It depends. A 4-speed is always 1 to 1 in top. That is, the engine RPM
and the driveshaft RPM are the same. Most 5-speeds have 4th as 1 to 1
and 5th is an overdrive of 15% or more (driveshaft spins x% faster than
motor).
Notably, BMW 5-speeds have been 1 to 1, with deep 1st gears, and a
numerically low rear axle ratio. This is actually a better idea as 1 to
1 is the most efficient 'gear' for a transmission. EG, with a MGB
overdrive, there is a lot of complexity, pumping, and whiring things to
provide that overdrive gear.
With an overdrive and extremely high speeds (130+) the driveshaft is the
fastest moving thing in the car and can cause premature wear and lotsa
vibration. The race car folks usually run 1 to 1 top with steep lower
gears and axle ratios less than 3.0 to one to limit wear on the
u-joints.
> I have also heard that somehow running the engine at high revs won't harm
> the car.
It depends. But generally higher engine speeds will eventually wear a
motor out faster. Of course, it may be long after you've traded the car.
Bob Allen, Kansas City, 69CGT, 75TR6, 60Elva
"A man of genuis makes no mistakes. His errors are volitional and are
the portals of discovery" -- James Joyce in "Ulysses"
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