406 with engine change

[Mike406]

Originally Posted by James Eastwood

Mike, just a couple of thoughts before you change your gear box, because 16mph/1000rpm doesn't sound right, that's more MG Midget or Mini territory.

I would raise a rear wheel and count the rear wheel to prop rotationss to check axle ratio.
Then I would set up a multimter to measure engine speed, and use a GPS speed App on my phone, work out the actual ratio you are getting between measured engine vs vehicle speed.

Have you counted the gear changes to make sure it is shifting into top gear? Is the auto box topped up with fluid?

The only explanation I can think off might be if the car originally had say a +15% over drive fitted, some manufacturers would lower the rear gear slightly (maybe 7%) to give the car better acceleration AND better top end cruising. Your auto box I expect will not have an over driven top gear but instead a straight thru 1:1 drive in top.

James

hi,
thank you for those thoughts
the car is away at the moment having the carburettors / timing tuned

so will check out when it's back

the Rover SD1 had the same gearbox as I have out in the Bristol, the big differences are that the back axle ratio was quieter different and they had 14" wheels as opposed to 16"

once again thanks for your help

mike