[Healeys] Overdrive ratios

[Bob Spidell]

Other way around. The ratio would be 1:1.28 (or 0.72:1.0). For instance, if the gearbox output is 1,000RPM, the O/D's output would be 1,280RPM. (a 28% 'boost' in ouput). Another way of looking at it is that the O/D reduces the engine RPMs by the stated percent. (if you switch on the O/D without applying more throttle, the engine speed will decrease). 


bs 

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Bob Spidell - San Jose, CA 


The Austin-Healey overdrive ratios are 28% and 22% which are the first 
two numbers in the serial number shown on the plate on the overdrive 
unit. How does that translate into figuring what the ratio coming out 
of the transmission is? For example, 4th gear is 1.00 to 1.00. An 
overdrive ratio would be 1.00 to (a number less than 1.00). Obviously 
it is not 1.00 to 0.28 or 0.22. Would it be 1.00 to (1-0.28) or 1.00 to 
0.72? 
Thanks. 
Charlie