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MG MGB GT V8 Factory Originals Technical - 3.5 V8 w MG Overdrive

Is a late model MG Overdrive a suitable mate to a 3.5 Rover? I'm wondering if it's strong enough with the added power a v8 would be putting out?
Any shortcomings to this combo?
Larry C

On factory the V8 early cars had overdrive on 3rd & 4th gears, as on the 4 cylinder cars. Problems soon led to them blanking off overdrive on 3rd as full throttle disengagement was breaking the overdrive. They retained the overdrive facility only on 4th where the higher gearing meant a reduction in torque. One must also bear in mind that this was with a low power Range Rover specification motor; if you build a V8 these days the odds are that you will use a motor from a Rover saloon, or similar, which is quite a lot more powerful even in standard form.

So, the short answer is: don't mess about with the standard MG 'box - junk it in favour of something which is designed to handle the torque of a V8.
David Daw

David is right about the history of the overdrive. The version of the 3.5 Rover V8 originally installed in the MGB GT V8 produced a mere 137 @ 5000 RPM. A more modern version will overstress both the original transmission and the overdrive as well. In the UK the most popular transmission for the V8 conversion is the one used in the Rover SD1. In the USA, the Chevrolet Camaro transmission is prefered.
Steve S.


I've been running an MGB/OD box for about 15 years behind a Buick 215 ('63 Skylark, 11.0:1 comp). I am on my second box but the first failure was not related to the OD. I had allowed the trans bolts to loosen (used too much anti-sieze) and was actually on my way to get new bolts when the clutch center hub broke. The car was quite a junker anyhow so I replaced the gearbox when building my current car about 12 years ago. The box has held up fine & I have quite a lead foot. After an oil change about a year ago it became sluggish on the first disengagement of the OD when cold. Changing again to straight 30W helped but did not cure it completely.

When I originally built this car the gearbox choices were more limited than now. I am currently building a 4.6 to replace the 215 and will use a '91 Camaro T5 trans. Despite my good experience with the MG box I think this would be the way to go if you can. (or other comparable late model trans). If you do use the MG box try to use a late model with the higher (numerically low) first gear.

Joe Collins

This thread was discussed on 13/05/2001

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