Terry, not all that far off what my table for gave for stock parts for my '76
1500. For 100mph I had 4750 revs, a heck of a lot better than the almost 6000
without O/D and that would be screaming! I agree on teh need for O/D at speed.
Sounds liek Laura ( and others) need a close ratio 5 or 6 speed rather than and
O/D? ratio for round town (or track?)
Alan
'76 Spitfire
Original Message:
-----------------
From: Terry L. Thompson tlt@digex.net
Date: Tue, 23 May 2000 14:40:00 -0400
Subject: Re: So, who wants to sell me a Spitfire OD tranny?
Just as a little caveat to the OD/NON-OD debate, the J-Type OD unit top gear
drops revs from 1.0:1.0 gear ratio to 0.79:1.0 gear ratio (if I'm
remembering correctly).
And although it doesn't seem like a large amount, the engine revs to do
60mph on my car is somewhere around 3000 rpms. With OD, I could do 60mph and
the rpms should read about 2400.
And at 4500 rpms (which I think is actually pretty screaming for a stock
engine) with 23.5" outside diameter wheels (880 revs per mile), a late model
Differential (3.89:1) and OD engaged, you should be able to do around 99
mph.
The Conversion Component's (in NZ) Toyota Celica 5-speed conversion, has a
5th gear ratio of 0.86:1.0 which would only be around 91 mph at 4500rpm with
the same 23.5" od wheels and 3.89 final drive.
And just to really make you think, I've heard of someone on the list that
had the swiss rear diff (3.63:1), and an engine he could take to 8000 rpms,
Assuming he had Firestone F570 185/70r13's (886 revs/mile) and OD (.79:1),
he should conceivably move his spitfire to around 188.91 mph .
This is obviously a theoretical observance.
(engine RPMS) divided by (trans gear rate) divided by (final drive rate)
divided by (tire rotations per mile) multiplied by 60 (# minutes in hour) =
Movement in miles per hour.
Terry L. Thompson
'76 Spit 1500 (which has never done more than 75 mph)
Maryland
http://www.access.digex.net/terry_t/index.html
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