ERF-NGC-European:
A very well-respected ERF man recently shared with me his calculations re RT versus RTO gearboxes in NGCs, as follows:‘As a datum point, we’ll take a an engine speed of 1800 RPM.
With an RT ‘box, this obviously gives a prop shaft speed of 1800 RPM in top gear.
With 10.00R20 tyres, and an axle ratio of 4.64:1, this gives a road speed of 47.3 MPH.
Substitute the 12.00R20 tyres of the NGC, and the road speed increases to 50.8 MPH.
Substitute the RTO ‘box, together with the 12.00R20 tyres, and the road speed increases to 58.4 MPH.
If we revert to a datum road speed of 50.8 MPH, with the RT ‘box the engine speed (as above) is 1800. With the RTO ‘box, it reduces to 1566 RPM.
In my opinion an RTO ‘box in an NGC would be over-geared for the torque characteristics of the 335 ‘small cam’ 855 series engine.
A ‘big cam’ 855 had very different torque properties, and would possibly suit an RTO gearbox better with the NGC’s axle/wheel size combination.’And as we know, there were only two NGCs with the big-cam 14-litre ■■■■■■■■■ one of which was the last to be despatched in Dec ’77.
Robert
Peak torque 930 lb/ft 1,500 rpm.Also 90 kmh motorway max ?.