I have an original 1300 MK1 sedan, 3 speed auto. I've had it up to 70mph, and that's about as far as I'll take it. My idea is to bolt in a 1600 kent and change the diff ratio to a higher gearing. So where do I start? thanks

if its an original phone number motor with an auto the diff ration is likely to be 4.125:1

Are you keeping the auto, because that will severly limit everything because a lower ratio will make it hopeless to get off the mark.

With a manual box go for a 3.77

Thanks for that. Yeah, I'm going to keep it auto if i stick with the xflow motors. But manual if I do a DOHC engine conversion.

I've got the very same set-up. Was 1300 auto (painfull to drive), fitted a formula ford spec 1600, kept auto and fitted 3.54 diff ratio and now is a delight to drive. Not a lot of power, but, from 40k to 120k motor is within 8hp of its maximum and so at any speed from 40-120 when you stand on the throttle it just accelerates and accelerates well.