I have had a 4.3 gear set ( from an MGA ) in my TD for over 20 years. I also
have an XPEG 1500 block in the car. With this 1500 engine setup, the 4.3
ratio is too low and I would install a 4.1 or even 3.9 next time. I have a
friend who has his TD block bored and sleeved to 72 mm ( 1500 ) and he is
very happy with early MGB 3.9 diff gears in his TD. We also run modern
radialk 165 x 15" tires.
One thing to remember is most modern radial tires ( 165 x 15" ) have a lower
profile than the original 5.50 x 15" bias ply tires so a single step drop in
gear ratio is probably required just to restore the original overall gearing
of the TD.
For my money, if I was using a 1250 engine in a TD or TF , I would use 4.3
gear set and be happy cruising at about 60-65 mph.
With a 1500 engine in a TD or TF, 4.1 or even 3.9 seems to work fine,
particularily with the smaller diameter modern radials.
Bob Grunau.
> > One of our club members has a '53 MGTD, and was asking if
> > there
> > are any kits available for his car which would increase the highway
> > speed. Perhaps an overdrive set up or tranny conversion to get more
> > MPH.
My understanding is that the MPAG's horsepower peaks at 5400 rpm with 50
BHP. This is the horsepower required to push the car 80 mph. The rear end
ratio of 5.125 (either by design or accident) yields 80 mph at 5400 rpm.
Therefore, changing this ratio in either direction will actually decrease
the top end capability of the car.
So ironically, overdrive will make the car slower with regard to top end. On
the other hand, a lower ratio is said to make the TD much more agreeable at
highway speed. I'm the only member of our local T series club that hasn't
converted to the MGA 4.3 rear end gears.
BTW: The book "MG TD &TF GOLD PORTFOLIO 1949-1955" by Brooklands Books has
lots of great stats and graphs on these cars.
Bob Donahue (Still stuck in the '50s)
Email - bobmgtd@insightbb.com
52 MGTD - NEMGTR #11470
71 MGB - NAMGBR #7-3336
.
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