report on 82 300cd stick conversion - Page 2 - PeachParts Mercedes-Benz Forum

#16 01-21-2008, 02:55 PM

Quote:

Originally Posted by Brian Carlton

I'm thinking that the power loss in the automatic is not directly proportional to the engine power. As an example, a 62 hp engine might lose 15 hp to the transmission. However, a 123 hp engine might lose 18 hp to a very similar transmission. The more horsepower available..........the less the proportional loss in the transmssion.

Remember, from 0-60, that torque converter provides quite a bit more output torque relative to vehicle speed..........hence the name.

My dyno tests show only a 6lb/ft decrease in torque (154 to 148) and a 12hp increase (87 to 99) when I switched to a manual.

Brian Carlton · #17 01-21-2008, 03:01 PM

Quote:

Originally Posted by ForcedInduction

My dyno tests show only a 6lb/ft decrease in torque (154 to 148) and a 12hp increase (87 to 99) when I switched to a manual.

It's not the peak figures that I'm referring to.

With a manual, your engine speed is directly tied to road speed. You can't get anymore torque from the engine if it puts out 70 lb.-ft. at 1200 rpm. You must wait until the revs climb.

With the automatic, the t/c allows the same engine to spin at 2000 rpm for the same road speed. This allows the engine significantly more torque to the wheels at that road speed...........and should result in a better E.T. to 60.

However, once the manual gets up in it's powerband, the automatic is at a disadvantage due to the losses in the t/c.

Of course the auto has the advantage of the faster shifts.

Many variables in a 0-60 time...........

Mark DiSilvestro · #18 01-21-2008, 07:38 PM

Quote:

Originally Posted by t walgamuth

Yes, another excellent reason to convert to stick.

BTW the modern automaitcs I think probably have a lot less loss than these old ones.

Tom W

The several reasons I bought my first diesel included reducing wear and tear on my daily-driver Nissan Altima, a dirts-cheap price for a 240D, looking for diesel experience and the possibility of burning alternative fuels. I wasn't expecting spectacular fuel economy and while my automatic 240D gets a marginally better city mileage of 20-22 mpg versus my Nissan's 18-20, on the highway the Nissan achieves 30 - 35, while the diesel manages 24-25 at best. Both cars have 4-speed automatics but the Nissan has an overdrive top gear. On the other hand my 240D's city mileage looks pretty good next to most of the gasser Benzes I've owned, which have lingered in the 13 to 15 mpg range.

Happy Motoring, Mark

t walgamuth · #19 01-21-2008, 10:25 PM

Quote:

Originally Posted by Brian Carlton

It's not the peak figures that I'm referring to.

With a manual, your engine speed is directly tied to road speed. You can't get anymore torque from the engine if it puts out 70 lb.-ft. at 1200 rpm. You must wait until the revs climb.

With the automatic, the t/c allows the same engine to spin at 2000 rpm for the same road speed. This allows the engine significantly more torque to the wheels at that road speed...........and should result in a better E.T. to 60.

However, once the manual gets up in it's powerband, the automatic is at a disadvantage due to the losses in the t/c.

Of course the auto has the advantage of the faster shifts.

Many variables in a 0-60 time...........

I think it might be possible to keep the turbo spooled on shifts if you are skilled enough with the diesel and the stick. My brother used to drive a diesel box truck for a living. Once I asked him to tow my diesel suburban to the repair shop when the automatic took a crap. We rope towed it. He was so good at shifting that truck without letting the rpm down that the rope never lost its tautness. It would sag a little but never go slack. I was truly impressed. I never suspected my little bro could shift so skillfully.

Tom W

Brian Carlton · #20 01-21-2008, 10:35 PM

Quote:

Originally Posted by t walgamuth

I think it might be possible to keep the turbo spooled on shifts if you are skilled enough with the diesel and the stick. My brother used to drive a diesel box truck for a living. Once I asked him to tow my diesel suburban to the repair shop when the automatic took a crap. We rope towed it. He was so good at shifting that truck without letting the rpm down that the rope never lost its tautness. It would sag a little but never go slack. I was truly impressed. I never suspected my little bro could shift so skillfully.

Tom W

The skill is not with regard to holding rpm's.........it's getting it into neutral without the drivetrain causing any braking on the tow vehicle. If the driver lifts the accelerator just the slightest bit early (just ahead of the clutch).........the drivetrain will slow the tow vehicle and the cable will go slack. If it's done really poorly, the towed vehicle will catch the towing vehicle.

If the towing vehicle gets to neutral without any drag.........both vehicles coast together during the shift........and the cable should not go slack. This example doesn't take into account the wind resistance on the towing vehicle which the towed vehicle may not suffer.

Dusty-NZ · #21 01-22-2008, 02:52 AM

My w115 240D was auto when I bought it , I drove it for a couple of years before converting it to manual.

Very pleasing result . Better mpg and faster acceleration .

The mpg improved by 4mpg. measured over several tank fills.

The acceleration improved by measuring speed up the motorway on ramp. I am now able to blend into the traffic flow at the speed limit rather than 8 - 10 kph below it.

The auto is definately a power+fuel sucking device in the little 240D.

I am doing the same change to the w115 300D for the same driveability reasons.

diametricalbenz · #22 01-22-2008, 04:24 AM

I am having my 240D converted to 3.0L and manual as well. It's a painfully slow process. I sure hope it meets my expectations when it's done!

t walgamuth · #23 02-02-2008, 02:18 PM

Quote:

Originally Posted by ForcedInduction

If only there was a 3.3x or 3.2x ratio to work with. The jump from 3.69-3.46 made a big (good) difference in acceleration and MPG, but going to 3.07 is too big a jump for me.

I have the 327 ring and pinion that came in my 190 16v diff available if you wanted that ratio.

I would make you a deal on it.

Tom W