To steal from GW Bush (but not to in any endorse any current candidate) I think
this is fuzzy math. It is not a 25% reduction, it is a 20% reduction, just like
the MGB OD trans. You have the numbers backwards. it is a 20% reduction, or a
25% increase - do the math. Here it is
No OD at 85.8 mph is 5250rpm
with OD at 85.8mph is 4194.9rpm
5250 * 0.8 = 4200rpm (within rounding error) i.e. 80% reduction - same as
4200 *1.25 = 5250 rpm (within rounding error) a 25% increase.
any 20% decrease from the high is the same as a 25% increase from the low - for
example:
If I have $100 and lose 20% there are $80 left. To get back to $100, I have to
make $20, and $20 is 25% of $80.
Phil Bates
Charley & Peggy Robinson wrote:
> OK, that explains why some of the numbers don't match. My question:
> Was there a L d'N OD with a 25% reduction?
>
>
>
> "David F. Darby" wrote:
> >
> > Subject: Re: OD transmissions on ZA MG and rear axle ratios
> >
> > > Bullwinkle wrote:
> > > >
> > > > CR:
> > > >
> > > > They also state that the 4.55/1 car did 85.8 MPH at 5250 RPM and the OD
> > car did
> > > > 90 MPH at 4400 RPM. Does that still work out at ~25% reduction?
> > -------------------------
> > > CR asked
> > > However, the non-OD final drive ratio in this example (4.55:1) is
> > > different than in the former one (4.87:1). Did they test more than one
> > > car?
> > -------------------------
> > The ZA utilized a 4.875:1 rear axle ratio. After a whopping 10% horsepower
> > boost in the ZB, the 4.55:1 was introduced. While the factory might have
> > played around with OD, I've never seen it listed as an option for the car.
> >
> > Regards,
> >
> > David F. Darby
> > http://www.mgb.bc.ca/mgz
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