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Date Posted: 16:40:10 11/24/01 Sat
Author: Bill 87S4
Author Host/IP: 205.188.200.56
Subject: Re: Technical definition (not necesarily Porsche related)
In reply to: Nicole 's message, "Technical definition (not necesarily Porsche related)" on 14:38:33 11/24/01 Sat

Nicole,

overdrive started life as a separate transmission which allowed for lower revs (higher speeds). My '49 Willys' Jeepster has a 3-speed transmission + an overdrive unit which will work in 2nd or 3rd gear (effectivly giving me 5 speeds). My normal shift pattern went: 1-2-3-3OD where you didnt change the 3rd to 3OD gear, you allowed the overdrive unit to engage in 3rd gear, giving you a 4th ratio.

overdrive now implies a ratio (usually the top gear) inside the transmission which is higher (numerially lower) than a 1:1. Depending on the rear end ratio, overdrive is not necessary, as in the 928(with its high/numerically low rear end ratio).... the top gear in a 5-speed 928S4 is a 1:1..... NO overdrive.

If the 928 had an overdrive, the top gear may be (hypothetically) .75:1 which would give lower engine rpms at the same speed as a 1:1 (non-overdrive) gear.

I'm not sure I'm making this any easier to understand.... best of luck figuring it out, I hope I helped!!

Bill
87 S4 5-speed

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Replies:

  • Re: Technical definition (not necesarily Porsche related) -- john928, 18:53:50 11/24/01 Sat
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