Kerry, in Imperials, high gear is already rather tall, almost like overdrive.
If you put overdrive on top of the 2.94 ratio, you have too steep of a gear
(like about 2.3). The engine will have trouble hauling the 5400 lbs on
anything but the straightest roads and/or at speeds over 80. Also, the
converter will waist a lot of energy even in the 70 mph range (I assume this is
the standard torquflite w/out the lockup). So, you don't have to, but if you
spend $2000 on one of these o/d gears, you may just as well do it right. If
you change the ratio from 2.94 to 3.23 for example, a .78 OD will give you an
equivalent of 2.52, which is still taller than 2.94, and still get better
acceleration at low speed. However, this gearing will lead to loss of top
speed. It turns out that at least for the 67-69's, the 2.94 final ratio is
fairly close to optimum for high speed performance. So, if I did this to one
of my Imps, I would go lower in final ratio, so that the overdrive would be
about the same as third gear is stock. Say, a 3.55 ratio would give 2.77 with
overdrive (well, may be I would reduce the driving tires aspect ratio to 70
from 75 to get about the same highway gearing). Does that defeat the purpose
of the overdrive? Not to me. The low speed acceleration will improve
substantially (I bet the car will do 0-60 in 7-7.5 seconds and 1/4 mile in 15.5
s or better from about 16.5) and also higher speed performance will improve too
(I will be able to use 3rd gear w/out OD up to 100-110 with the engine close to
its peak power before shift to overdrive). This may be one of the best
performance enhancements you can do to an Imp in terms of $/performance, except
may be for dual exhaust and cam upgrade.
D^2, 2x68
Quoting Kerry Pinkerton <pinkertonk@xxxxxxxxx>:
> D^2, why would you have to change your rear end ratio? It's not 'full time'
> overdrive is it? I'm under the impression that all overdrives (including
> Gear Vendors) can be 'selected' when you want the extra legs. Yes with the
> gear vendors add on box, you COULD run it in OD all the time but that would
> defeat the purpose and you could get the same results with much less expense
> by changing the rear end ratio.
>
> Kerryp
> http://dte.net/57imperial
> KaP Imperial Services - Patch Panels, Metalshaping, Restoration
> Manufacturer of high quality Wheeling Machines
> ----- Original Message -----
> From: <dardal@xxxxxxxxxxxxxxx>
> To: <mailing-list@xxxxxxxxxxxxxxxx>
> Sent: Monday, February 02, 2004 8:25 AM
> Subject: Re: IML: Please Welcome Carl Falletta
>
>
> > Quoting Dick Benjamin <dickb@xxxxxxxxx>:
> >
> > > I urge you to think again before modifying any old car, especially one
> this
> > > rare and nice. If you want a car with lockup torque converter, consider
> > > adding an 81-83 EFI coupe to your collection.
> >
> > I have a lockup converter in my 68 LeBaron. The transmision is most
> likely a 78
> > torqueflite for 440's. The 69 440 installed on the car had a bit too much
> > torque for the transmision, however after a shift kit (increased pressure)
> and
> > external oil cooler, it looks like the transmision can handle the 440. As
> for
> > the advantages of the lockup torque converter, they are noticeable mostly
> > around town where the speeds are low and converter slippage is high. At
> over
> > 70, there is little difference. If you want to install a 4 speed
> transmission,
> > follow Dick's advice and stay away from the A-904's. As an alternative,
> "Gear
> > Vendors" builds an overdrive electric system that bolts on to the
> torquflite.
> > These are expensive ($2K) but they are supposed to be very tough. You
> would
> > have to change your dif. ratio, as the final ratio would be too tall. A
> lower
> > gear will give you better accelerations in city traffic as well.
> >
> > D^2
> >
> >
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