Hello Dave. Thanks for the data. I'm attaching the text of a response from
Alan B., which has come to the same conclusions. His tire size for
computing was 26" while yours was 25.14 (if my math is correct). The
difference in tire size probably accounts for the 3 mph difference.
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Hey Mike
Some assumptions first:
Tyre diameter is 26". Let me know your real tyre size and I'll adjust the
figures.
BN2 has the original four speed gearbox with a 28% overdrive
BN2 has standard 4.1 rear axle ratio.
If so:
3000rpm in top gives 57mph
3000rpm in o/d top gives 73mph
Changing only the back axle gearing to 3.54
3000rpm in top gives 66mph
3000rpm in o/d top gives 84mph
Let me know if that helps.
AlanB
UK
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----- Original Message -----
From: "Dave & Marlene" <rusd@velocitus.net>
To: "M Lempert" <mlempert@bellsouth.net>
Cc: <healeys@autox.team.net>
Sent: Wednesday, May 04, 2005 7:16 PM
Subject: Re: BN2 revs at speed
> Hi Mike,
>
> I have read varying reports for numbers on this. Others may differ.
>
> My BN2 with P175 Michelin tires (6.58 ft. rolling circumference), & 28%
> overdrive, at 3000 rpm, runs 63 mph in direct & 81 mph in od.
>
> Note that a 28% od gives an overall gear box ratio of 0.78. This results
> in a final drive ratio of 2.76/1 with the 3.54 axle in od.
>
> The original speedo calibration of 1325 rev/mile with 4.11 axle &
> slightly smaller tires, needed to be changed to 1137 rev/mile on my car.
>
> The long stroke four cruises very nicely at 3000 rpm & 80 mph.
>
> Getting rolling from a stop is no bother whatsoever. It will still spin
> the tires considerably if you wish. Not that I would do such a thing. It
> actually makes first gear good for something now.
>
> I still have my set of new 3.54 gears. During the long wait, I got a 3.54
> complete center section from Earl Kagna.
>
> Regards,
> Dave Russell
> BN2
>
> M Lempert wrote:
> > I'd appreciate some data from BN2 owners out there. If you know your
> > OD% and also have the original gearing, can you tell me your speed
> > at 3000 RPM ? In fact, it would be good to know the speed both in and
> > out of OD. I realize there will be some differences due to tire
> > size and speedo accuracy.
> >
> > If anyone with a 3.54 installed wants to compare, that will be good
> > data as well. However, what I am trying to assess is my own BN2
> > situation. Believe it or not, I haven't installed my 3.54 in it yet.
> > I want to determine my starting point before opening things up. I'm
> > suspicious that I might already have a higher ratio than stock.
> >
> > Thanks much.
> >
> > Mike Lempert
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