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Discussion Starter #1
is there any DIFFerence between a manual and automatic diff? That's the car being manual or auto of course. Am i right in thinking that the same car would have a higher road speed, for the same engine rpm, if it were fitted with an auto diff rather than a manual one?
 

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Automatics do tend to have a higher top speed, but generally it's not significantly higher. I think you mean to say Manual or Auto Transmission not diff :)
 

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1984 190e 2.3
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manual had more grip with the clutch. so more of the engines power is transferred to the wheels. on an automatic, the torque converter slips, so not all power is transfered to the wheels. that also is a factor for the manuals fuel efficiency. the automatic and manual end up with the same gear ratio by the 4th gear (around 1:1). but manual has a 5th gear that auto doesnt. the 5th gear gives the manual a higher top speed.
 

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Hi guys. Thanks for the advice but you seem to have missed the mark somewhat. It's probably better if i explain the car better and maybe you'll understand why i chose my user name to. The car is a 1987 190e with a very sick (ie wornout) engine, so i'm in the process of fitting a 3.5 Rover v8 with manual shift. Obviously with this sort of torque, the gearing will probably be way too low, so i was considering fitting a different ratio diff to compensate. Realise it's getting a bit technical now and i have most likely upset some folks by treating a Merc in such a way, but hey what the hell. It's still a damn fine looking car. Can't wait to drive it with the new motor in. Maybe i should've taken the 380sel engine and auto box i was offered for it.
 

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the butcher - 2/24/2005 3:32 PM

Hi guys. Thanks for the advice but you seem to have missed the mark somewhat. It's probably better if i explain the car better and maybe you'll understand why i chose my user name to. The car is a 1987 190e with a very sick (ie wornout) engine, so i'm in the process of fitting a 3.5 Rover v8 with manual shift. Obviously with this sort of torque, the gearing will probably be way too low, so i was considering fitting a different ratio diff to compensate. Realise it's getting a bit technical now and i have most likely upset some folks by treating a Merc in such a way, but hey what the hell. It's still a damn fine looking car. Can't wait to drive it with the new motor in. Maybe i should've taken the 380sel engine and auto box i was offered for it.
A Rover engine??!! No SBC engines where you live? A pity. Anyway, and speaking very generally, the HIGHER the final drive is numerically, the slower a car will be at a given RPM. The LOWER the final drive is numerically, the faster the car will be at that same RPM. In theory you can go lower and lower (numerically) on the final drive ratio and gain more speed with each change, but unfortunately max engine power depends on a specific rev range, so if it's turning over too slowly to reach max power, the car's top speed cannot be reached.
The ideal gear for any final drive is dependent on a number of factors, but a full explanation would have me prattling on and on. Best bet is to Google the topic, or better yet (perhaps) dogpile.com
 
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