At 01:31 AM 1/7/99 EST, Rick Ewald (REwald9535@aol.com) wrote:
>In a message dated 1/6/99 8:22:03 PM Pacific Standard Time,
>barneymg@ntsource.com writes:
>> Less friction loss in top gear.
>
>Barney,
>Come on the friction loss would be greater than the advantage of a .71 to
1 ratio? I would have to think that the friction loss in a Laycock
overdrive would be greater than the friction loss of a simple 5th gear. So
if what you say is true, then the LBC owners with overdrives would get
lower fuel mileage in OD then either they or I would in 4th.
No, the friction loss is not greater than the advantage of the overdrive
ratio. And it is almost certainly less than the loss in a Laycock
overdrive unit. My original comment was only in response to the difference
between a 5-speed with direct drive top gear and one with overdrive top
gear. If a numerically lower gear ratio is used for the final drive (maybe
3:1 vs 4:1), then the top (5th) gear can be direct drive, which will have
less friction in the gearbox that an overdrive top gear.
OTOH, the lower ratio final drive might have more friction for all I know.
One more related note. At least some of the GM 6-speed gearboxes for high
performance models (Corvette, Camaro, Firebird) have two overdrive gears to
accomodate the much higher top speeds. In this case 4th gear is direct
drive, and 5th and 6th are both overdrive ratios.
Barney Gaylord
1958 MGA with an attitude
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