desert replied:

I say negative. The 4.1 ratio will work well. I ran the 6.2 in a 75 series. If he wanted to reduce hwy revs he can always go up a size in tyre. However, if you were to change to 3.7 (and I have my doubts that ratio is available for the 80), then it could well prove to be a backward step for off-road work. Follow?

Topcat (WA) replied:

Hi Lionel,
I have 3.7 diff ratios in my 75 Troopy which has a 6.5 chevy diesel & the only reason I did that was I wanted my highway cruising speed to be 100kph @ 2000 rpm which is the enconomical rev range for the chevy. Both the 6.2 & 6.5 have plenty of low down torque to go to high speed diffs for off-road driving. You could even go as low as 3.5:1 if you could get the ratios (I couldn't because my front diff is not the same size as the rear which are in the earlier model cruisers).
Since he has spent all that money on diff lockers I would advise staying with the existing diff setup unless he has the money to splurge on it. If he was going to do it then it would have been less costly doing it when had the lockers fitted. Also fitting high speed diffs gives a wider 1st to 2nd gear rev band otherwise you may as well start off in 2nd gear with the chevy fitted. Cheers.

Member - Shane D (QLD) replied:

He can easily lift the gearing by putting bigger tyres on if need be.

Toyota run same diffs for petrol and deisel (most of the time) and I wouldn't think that it would be necessary, having said that I don't know how hard you can push those chevy deisels, rev wise but there should be plenty spare at 100ks.

Shane