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MG MGB GT V8 Factory Originals Technical - Overdrive necessary?

Soon plan to have a v8 installed (not a mechanic).My trusted mechanic strongly advises going with a new tranny w/overdrive.Can see the obvious advantages, esp. highspeed travel, but up to now, rarely drive on superhighways at 70-80mph. Trans. in car is in good shape & wonder if replacement is really necessary?
m chiola

He is probably talking about a 5 speed..
CW Strong

T5 Camaro or Rover SD1 5 speed if this is a BOP/R V8.
-BMC.
BMC Brian McCullough

Word has it that the MGB 1800 type transmission is barely up to handleing the 140BHP GTV8 of the '70's. Anything more than that, and that's just about every post 70's V8, will destroy it. I know that on the GTV8's the factory blanked off o'drive for third gear because of this marginality.
My own modest, standard unaltered straight out of a range rover EFI V8 would have to be around the 180 BHP mark . The Rover sedan motors put out more power. A little head work and you get more.
You will need another transmission and tail shaft.
I'm using a toyota supra box because it easily fits in the tunnel and because the adaptor bell housings are made in Sydney. Dellow automotive, application is Rover V8 or Leyland P76 (MGB not mentioned). They ship world wide. In the US you have many more choices, each with its' pros and cons.
If you have a later Salsbury diff' this can deal with anything under 220BHP, it was orrigionaly designed for a small truck. The earlier banjo diff' might give problems. How can you tell?. The salsbury diff' has a cover on the back, ie circle of bolts visible on the back/rear, none on the front. The banjo has a circle of bolts visible on the front.
Rubber bumpers had Salsbury's, and , I think, back to at least '72. I don't know for sure, go and look at the front of your diff'!.
Peter

Click the WWW enthusiasts logo in the top LH corner of this site/page, then choose/click 'MGB MGBGTV8' and then click on 'V8 Conversions Overview' at the bottom of that page. There's a detailed artical by Roger Parker that is most informative.
Peter

As Peter stated, the best reason to use another transmission (5 speed preferably) is increased strength and less chance of failure. As said, there are a couple of modern 5 speeds that fit well and offer increased strength as well as improved gearing. You'll be much happier in the long run I'm sure.
Bill Young

You will need an overdrive 5th gear if you are running the MGB 3.9 differential ratio.
Edd Weninger

This thread was discussed on 19/04/2006

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