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  #1  
Old 06-20-2008, 11:40 AM
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swap 3 speed to 5 speed in 75 450sl

Hi,

Would like to switch 3 speed in 75 450sl (eng# 117 982 12 039621 vin# 10704412024954) to 5 speed to increase gas milage. Does anyone know what auto trans would bolt on.

Joe R.
Millersville, Md.

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  #2  
Old 06-20-2008, 11:58 AM
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Bolt on? Probably none.
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  #3  
Old 06-20-2008, 06:13 PM
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As 450slcguy said there are none. The 4 & 5 speed are not interchangeable with 3-speed 450 engines due to different bolt location holes on the intermediate plate.
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  #4  
Old 06-21-2008, 12:45 AM
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Adding gears wouldn't do much for mileage anyway. A taller rear axle ratio might help a bit but what you really need is a smaller more efficient engine and a lighter chassis. Poor fuel economy is in your car's DNA.
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  #5  
Old 06-21-2008, 02:29 AM
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It does make me wonder, though...how are they getting 3.8L V-6 engines to produce 265 HP (in a Hyundai Azera, yet), whereas my 3.8L 380SL produces (maybe) 150HP or so? And the Hyundai gets 17/26, and weighs only 50 pounds less. I think I know part of the answer - the head design and engine management of modern cars is light-years beyond the 116/117 (the 380's compression is so low it could have been equipped with an emergency starter hand crank). BTW, the Hyundai has a CVT - this is the most poweful engine I've ever seen mated to one.

Are the aerodynamics of a 107 THAT bad, or are modern cars just that good?

Everyone up to this point has been interested in interested in swapping BIGGER engines in cars, I'm wondering about swapping a SMALLER, more efficient and potentially more powerful engine with better gas mileage potential into a 107. At this point the only candidates with RWD would be luxury cars and trucks.
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  #6  
Old 06-21-2008, 09:20 AM
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Quote:
Originally Posted by deanyel View Post
Adding gears wouldn't do much for mileage anyway. A taller rear axle ratio might help a bit but what you really need is a smaller more efficient engine and a lighter chassis. Poor fuel economy is in your car's DNA.
The 722.6 Transmission has 5 gears with the last gear overdrive it also has a lockup converter. These features were not even available in the later 560SL. If they will bolt up, and I wish I would have checked while I had them side by side the 722.6 should increase gas mileage.
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  #7  
Old 06-21-2008, 09:22 AM
88Black560SL
 
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Quote:
Originally Posted by Strife View Post
It does make me wonder, though...how are they getting 3.8L V-6 engines to produce 265 HP (in a Hyundai Azera, yet), whereas my 3.8L 380SL produces (maybe) 150HP or so? And the Hyundai gets 17/26, and weighs only 50 pounds less. I think I know part of the answer - the head design and engine management of modern cars is light-years beyond the 116/117 (the 380's compression is so low it could have been equipped with an emergency starter hand crank). BTW, the Hyundai has a CVT - this is the most poweful engine I've ever seen mated to one.

Are the aerodynamics of a 107 THAT bad, or are modern cars just that good?

Everyone up to this point has been interested in interested in swapping BIGGER engines in cars, I'm wondering about swapping a SMALLER, more efficient and potentially more powerful engine with better gas mileage potential into a 107. At this point the only candidates with RWD would be luxury cars and trucks.
I'm thinking of an MB diesel 107 for my next project.
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  #8  
Old 06-21-2008, 06:06 PM
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722.6 electronic 5 speed gets no better mileage than the 722.5 5 speed - e.g. EPA rating of 1997 S320 versus 1996 S320, both 17/24. 722.6 5 speed gets only slightly better mileage than a 722.3 4 speed and that on the highway only - e.g. 1996 S500 (15/21) versus 1995 S500 (15/20). The idea that more gears necessarily offers better fuel economy is widespread but seems to be overblown if not just sales BS. More gears allows the engine to operate near peak efficiency more often but results in more shifts which are inefficient. In manual transmissions it actually seems to be the other way around - fewer gears offers better fuel economy. Corvettes sticks skip gears to avoid gas guzzler tax. Saab put out a bulletin in a prior fuel crissis telling their customers to skip gears (1 - 3 - 5) for better gas mileage. I've noticed over the years that 6 speed sticks will ususally have lower EPA ratings than the same car / drivetrain with a 5 speed stick. But still the myth persists that 6 speed sticks offer better fuel economy. The other great myth is that 6th gear of a 6 speed is necessarily taller than 5th gear of a 5 speed, as if they are taking the same transmission and tacking on extra gear.
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  #9  
Old 06-22-2008, 10:57 AM
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Unhappy 3spd to 5 spd

Thanks guys for the info. Guess I'll just have to suck it up and pay for the gas.

Joe R.
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  #10  
Old 06-22-2008, 03:59 PM
88Black560SL
 
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Quote:
Originally Posted by deanyel View Post
722.6 electronic 5 speed gets no better mileage than the 722.5 5 speed - e.g. EPA rating of 1997 S320 versus 1996 S320, both 17/24. 722.6 5 speed gets only slightly better mileage than a 722.3 4 speed and that on the highway only - e.g. 1996 S500 (15/21) versus 1995 S500 (15/20). The idea that more gears necessarily offers better fuel economy is widespread but seems to be overblown if not just sales BS. More gears allows the engine to operate near peak efficiency more often but results in more shifts which are inefficient. In manual transmissions it actually seems to be the other way around - fewer gears offers better fuel economy. Corvettes sticks skip gears to avoid gas guzzler tax. Saab put out a bulletin in a prior fuel crissis telling their customers to skip gears (1 - 3 - 5) for better gas mileage. I've noticed over the years that 6 speed sticks will ususally have lower EPA ratings than the same car / drivetrain with a 5 speed stick. But still the myth persists that 6 speed sticks offer better fuel economy. The other great myth is that 6th gear of a 6 speed is necessarily taller than 5th gear of a 5 speed, as if they are taking the same transmission and tacking on extra gear.
This sounds about right. I'm not sure if the major increase in that 1 mpg is causes by the addition of a 5th gear or a lockup converter. A lock up converter easily explains 1 mpg on highway. But I don't know when MB finally installed a lockup converter. I don't believe my 88 560SL has one. I also believe that real world city gas mileage will increase with 5 vs 4 gears. especially for people that drive harder that the EPA profile.

I'm not familiar with Saabs 1 3 5 suggestions but if this were an early 70's suggestion that would make sense especially for carburetted and even for open loop Djet type fuel injection systems.

In the 70's it was not uncommon the see standard shift cars getting less MPG and costing more than automatics. This was caused by throttle motions required during a shift causing an increase in emmisions requiring additional controls.
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  #11  
Old 06-22-2008, 06:41 PM
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With some careful tuning, you should be able to boost that 450SL from 9mpg to perhaps 14mpg. Which would be a noticable savings. But to change the transmission, you're looking at some major surgery which will never, ever pay for itself. For instance, the correct 4-speed that mates up to the motor will cost you about 1,000$ along with the clutch, flywheel, shifter, pedal, etc.

-CTH
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  #12  
Old 06-22-2008, 07:15 PM
88Black560SL
 
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Quote:
Originally Posted by cth350 View Post
With some careful tuning, you should be able to boost that 450SL from 9mpg to perhaps 14mpg. Which would be a noticable savings. But to change the transmission, you're looking at some major surgery which will never, ever pay for itself. For instance, the correct 4-speed that mates up to the motor will cost you about 1,000$ along with the clutch, flywheel, shifter, pedal, etc.

-CTH
I was under the impression we were talking automatics. I think a 4 speed from a later 560SL would bolt in they are both 117 engines???.
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  #13  
Old 06-24-2008, 03:31 PM
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Engines 117.982 to 117.985 have different assembly bolt location for trans than 117.986 onwards and only 3-speed boxes are available for those engines. And there is no 4-speed manual box for the 450 SL/C as Mercedes has no homologated manual box for this 450 engine.
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  #14  
Old 06-26-2008, 04:01 AM
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Quote:
Originally Posted by Strife View Post
It does make me wonder, though...how are they getting 3.8L V-6 engines to produce 265 HP (in a Hyundai Azera, yet), BTW, the Hyundai has a CVT - this is the most poweful engine I've ever seen mated to one.

Are the aerodynamics of a 107 THAT bad, or are modern cars just that good?

Everyone up to this point has been interested in interested in swapping BIGGER engines in cars, I'm wondering about swapping a SMALLER, more efficient and potentially more powerful engine with better gas mileage potential into a 107. At this point the only candidates with RWD would be luxury cars and trucks.
Actually the Azera comes with a 5 speed auto, I think the Nissan Maxima has a CVT mated to a 250+ hp V6. Aerodynamics is another concern, they make a huge difference, especially in highway mileage.
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  #15  
Old 06-26-2008, 08:15 AM
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In my oppinion a closed loop engine management system is the best approach to better fuel consumption such as megasquirt and if you're into software rather than hardware maybe easier than trying to custom make a geabox adaptor.
I've recorded my consumption over the last 3 years and averaged 14mpg with mixed driving conditions, this is all they achieved off the production line.

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