diesel aaz gearbox ratios, changing box etc

[specialshoe]

Hi all

I have an AAZ lump bolted up to an ACP gearbox which has a final drive ratio of 5.83 - which is a four speed original 1.6 or 1.6 diesel box.

There is large diameter tyres on the rear - big as will comfortably go under the arches

So this means its a bit of a revver - no rev counter but it is comfortable at 50mph / 80kph. It seems happy to go to 62 / 100 but it is thrashing round fairly - or sounds like it is - but might not be as there is no rev counter.

I want to work out the engine revs at say 50mph - so I can tell if it is thrashing too much or if it just sounds like it.

So the listed final drive raito is 5.83 - presumably to one - is this the ratio of the fourth gear input to the final drive i.e. with the van in fourth every time the diff rotates once the diff input spins 5.83 times.

Or is it that THE final drive is between crankshaft and diff - engine spins 5.83 times to every one diff rotation.

And heres another question - I did look in the archives but couldn't find the answer........

is it better to change the whole gearbox to get a lower ratio i.e. better cruising speed, or is it better to change the differential in my existing gearbox? Looking at the charts the gearboxes from the 1.9 dg engine vans with a 4.83 final drive have similar (if not the same) ratios through the gears but just a differnet final drive ratio - so as the 1.9 petrol box should be the easiest to get hold of - replace my diesel box for one of those.

Or just put up, shut up and let the engine spin faster than one might choose on the basis that if it has oil and is cool it won't come to any harm?

How can one rig up a rev counter to monitor engine revs - and what is an AAZ happy spinning at for long periods such as on the motorway ?

Anybody point me in the right direction please.

thanks