Assuming a 10 to 1 reduction ratio (pinion teeth to ring gear teeth):
Twin-Cyl Engine 9.0ft/lb per litre
Four 5.3 "
Six 4.6 "
Eight 4.2 "
Twelve 3.8 "
Source "Automobile Electrical & Electronic Eqpt" Young & Griffiths rev. Fardon, Butterworths press.
John.
"It's not always a case of learning more, but often of forgetting less"