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| 6 cyl Bristol cars Type 400 to 406 - restoration, repair, maintenance etc |
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23-06-15, 06:46 PM
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Depends what crown wheel and pinion is in the differential. The standard ratio will give c20mph/1000 revs on a Michelin X tyre. The overdrive bumps this up to c25mph/1000. The o/d does make a huge difference; especially if you are thinking of some serious journeys. Less revs = better mpg + less wear all round.
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23-06-15, 09:23 PM
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Thanks for that information.
At the moment I have a ZA Magnette & changed the final drive from 4.55:1 (around 15mph:1000!) to 3.9:1 from an MGA mk2 -this meant I was able to cruise at 70-75 (around 4000rpm) & get 32mpg on the Autobahn last year! An overdrive is difficult to fit to the ZA without transmission tunnel surgery. O/D has to be the way to go, my old TR3A was useless without it! So I have to factor that in to my costs! Further to fuel, does the head need to be "unleaded" or just use the additive &98 octane? David
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