If I buy a manual car, generally it will have 5 gears. Some autos have 4 speed.
Does this mean that an auto in top gear would be pulling higher revs, so there would be more engine noise when cruising at 70mph, or does an auto 4th gear equal a manual 5th gear?
Does this mean that auto 1/2/3 equal manual 1/2/3/4?
I'm confused!
Thanks.
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I can't vouch for other manufacturers, but 5th gear in one of my old manual gearboxed Cavaliers, gave the same amount of rpm as an auto cavalier in 4th gear that I owned afterwards. Same 2.0 litre 8 valve engine in both.
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That would make sense. I did read that some auto boxes in 4th than a manual in 5th as the have slightly better gearing.
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My Nissan Terrano with a 4 speed auto box actually has a higher ratio 4th gear than the 5th gear on the manual version. With a mechanical lock-up this gives lower revs when cruising and potentially better fuel consumption.
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Top gear in both is typically about the same, as is first gear. The auto has the benefit of a torque convertor though, which will typically have a 1:1 - 2:1 torque conversion range, meaning that effectively the auto has more 'gear ratios' between 1st and top gear than the manual.
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Not sure if this applies to the current crop of 5,6 and even 7 speed autoboxes but usually the auto top gear is marginally higher than the manual's top gear - the majority of the autos produced mid-late '90s would be geared higher than their manual counterpart. I know from experience that it's certainly true of the 5 series (both E34 and E39) and the Vx Omega.
Chad.
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Just to qualify ... I should have used the term "mph per 1000rpm" as this would take into all the various drivetrain ratios not just the gearbox...
:-)
Chad.
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Just off on a tangent... the newer Merc's have TWO reverse gears, and 7 forward.
Could somebody please explain this to me ...
I use reverse merely as a 'crawler' on the Astra (auto). Couldn't imagine, even on wet ice, why anyone would need TWO reverses!
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The Merc gearbox is probably a 4-speeder with a two-speed final drive (not dissimilar to high and low boxes on some 4x4s) The cross-over point (gear X in low = gear Y in high) is the 'lost' gear from the eight forward ratios.
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