Performance upgrades for 71 250? - Page 2 - PeachParts Mercedes-Benz Forum

Ron C. · #16 03-15-2003, 10:55 AM

Some ramblings... My '70 280SE, with the floor shift automatic..When shifted manually thru all the gears
goes way fast ...Is there a difference between the 108 and 114 ..Or am i just lucky it all works right..

Also.. According to the history of the 240Z its 6 cylinder engine is a direct descendant of the Merc engine, as Datsun owned a subsidiary named Prinz (sp?) that made a 6 cyl engine in the 60's under license from mercedes... Sooo the conversion ought to be doable..

Mark DiSilvestro · #17 03-15-2003, 12:02 PM

Ron C,
I suggested the Datsun Z engine transplant because of the similarity to the Mercedes design, because the Datsuns were often sold with 5 speeds, and Z engine performance mods might be more widely availible. The Z transplant would be more complicated by the Datsun manifolds being on the opposite side of the Mercedes location.

I've driven other vintage Mercedes Automatics that were more responsive than my 250 sedan. I remember a friends' beat up, rusty '70 250C automaic that drove like it had a V8 under the hood! The autobox in my '72 250C feels better that the one in my sedan, so I agree
being "lucky it all works right" has alot to do with it.

A few years ago, I tried out a '69 280S with a manual shift. I was suprised how much more responsive and fun it felt, even with the heavier body and the '4 on the column'.
For the same reason I prefer my manual 220S over my auto 250. My 250 Zenith carbs have been reliable so, if I could wave my magic wand, I'd just have the manual floorshift, preferably a 5-speed.

I'd like to know how far 'Snubway' plans to go with his 'souping-up the 250' project.

Happy Motoring, Mark

#18 03-15-2003, 07:56 PM

Good lookin out yall...

Just picked the car up today, its 72 250 not 71, off white, blue interior. 73,000 miles (original miles) even the paint is original, only a few chips and a couple dings. I checked out the exhaust it does have the dual pipes running the whole way. I wouldn't mind throwing on a different muffler and some chrome tips tho. The carbs need some adjustment they seem to load up when your idling and takes off kinda funny. Gotta ease on the gas. I'd like to do the webber conversion tho. Aside from that everything is real nice. I feel like a bandit getting it for $1000. Funny thing is, on the way to pick it up me and my dad saw one just like it, not as nice shape for $5,500

anyways I'll get back to yall on the progress (if any lol)...

I'd definately like to do the webber carbs and pertronix ignition. Whats the story on the manual shift for an automatic tranny? Is that an aftermarket type thing? Like I got a B&M shifter in my 70 Chevelle which will let you shift through the gears manually if you want.

holler back...

Mark DiSilvestro · #19 03-15-2003, 08:15 PM

You can manual-shift the automatics but some, in search of better performance, have removed the automatic transmission and installed a clutch and manual gearbox.

Happy Motoring, Mark

#20 03-16-2003, 03:53 PM

Yall ain't gonna believe this... So I go to look at the carbs, take off the air cleaner and what do I see........ Two WEBBER carbs already on it! Quite the pleasant suprise. I did notice their was a leak in the vacume tho so I'ma fix that and tune this carbs a bit if I can... this deal keeps gettin better....

psfred · #21 03-16-2003, 04:39 PM

Snubway:

you will find the automatic a little slow -- has a fluid coupling (as described above) rather than a torque converter, so you loose low end performance. If you want to go fast, floor it and KEEP THE PEDAL DOWN, or it will upshift immideately you lift off the kickdown switch (electrically operated).

It will also rev VERY high by US standards -- the engine will go 6600 rpm or so, but that is only 115 mph with the factory rear end. Feels strange, but it works.

The webers are much better than the Zeniths, also much easier to keep in tune. Fixing the vac leak will cure the idle/takeoff problem.

If you have ignition problems, ditch the factory transistor system and get a Crane or Pertronix, they are MUCH cheaper than a replacement ignition box. Those can be fixed, usually, too -- the main switching transistor goes bad and can be replaced with one from Radio Shack.

Other than that, performance mods are pretty much out except for finding a 4.5 in good shape. The engine, tranny (3 speed with torque converter) and rearend/driveshaft will fix you right up -- specs are 0-60 in 9.5 sec, top speed around 125 mph.

Horsepower on that six is pretty good for the size, anyway -- remember, its 2.5L, same size as the four in a mid 80's Century or Celebrity.....

The SE (mechanical fuel injection) engines will fit, as will all Benz v8s up to 96, ditto for all Benz sixes. I'd avoid the mechanical injection unless you want to spend some serious money....

If you REALLY want to ruin a classic and stick a US engine in it, you will have to use a Ford -- oil pump is on the front on all Benz engines, not the rear, and the cross member will be in the way.

Peter

slotjocko · #22 03-16-2003, 07:21 PM

Mark,

I didn't know there was snow in Miami! Dang!

Warren...u r killing me with www.engrish.com! I'm a 6'8" US transplant that was born and raised there. I will have fun with that site.

As for 5-speeds, sure would love to hear a solution. I still drive my '72 108 4.5 auto, but the SE Coupe is new to me. Although someone already sex-changed her to a 4-speed, it sure would be nice to be able to run through 5 forward especially up and down the mountain.

#23 03-16-2003, 07:28 PM

Just an amplification on the remark that you can only use a Ford engine because of the front oil sump location. I was considering a similar engine swap and considering a Chevy engine because of availability of performance and accessory items. I was informed that it wasn't a problem of adjusting the oil pickup tube and manufacturing a front sump oil pan to suit the Mercedes installation. The quoted price for a 383 hi torque engine installation was $5000. equivalent to the price of a Mercedes overhaul. Just passing this on for info

#24 03-16-2003, 07:40 PM

yea I was also thinking about the chevy transplant, I heard it is possible. The upsides to that is I got like 3 small blocks and a big block layin around, plus a turbo 350 tranny. hmmmm, wonder if you could modify a 12 bolt rearend to work lol.... good think about chevy's, cheap and easy to fix...

psfred · #25 03-16-2003, 08:17 PM

Why not just stick in a 560 engine? More horsepower, it fits (the Chevy WON"T unless you cut the subframe, you CANNOT move the oil pump to the other end!) and the tranny will bolt up.

Rear end is no go -- this is an offset diff swing axle, the diff goes on one side with a universal in the center (crawl under and take a look).

Besides, it worth MUCH more in stock condition!

Peter

Mark DiSilvestro · #26 03-16-2003, 09:35 PM

A couple more details....
We're talking about the W114 250 series which has a semi-trailing independant rear suspension. You still can't throw a Chevy rear end back there but maybe you could figure out how to make a 450SL/560SL differential work if you decide to drop in a V8.

The US market 70-72 250 had the M130 2.8 liter six, due to the increasing toll of US emissions regulations on power. It also added a few extra horsepower until the 1972 model year, when the compression was lowered to accept unleaded regular fuel, as premium unleaded wasn't widely availible then.

Happy Motoring, Mark

psfred · #27 03-16-2003, 09:48 PM

I must need new glasses, though the ? was an S.....! That would make it a 71 W108.

In that case, the V8 won't fit at all unless you remove the front suspension completely and replace it with something else. The upper control arms will occupy just about exactly the same space as the exhaust manifolds (ha!). You must also remove the two brace tubes that run from the firewall to the front frame extensions, and I suspect this will reduce the strength considerably.

Best bet for more power here is the DOHC 280 six with fuel injection, 76 and later. More power, you get rid of the carbs, and it bolts right in. The tranny from the later model will fit, and you can convert the carb version (4A1 4-barrel) to FI by exchanging the manifolds. Bolt holes for all the extras are already present (warm up regulator, etc).

Diff still won't fit, unless you can manufacture some fittings for the half shafts. I'd personally not replace the semi-trailing arms with a live axle.

Peter

#28 03-16-2003, 10:08 PM

Yea I for sure ain't into re-doing the whole car just to put a chevy in I don't care that much about it. If I want horsepower I'll drive the Chevelle lol. I'll just do what I can to this engine, and make the car look nice throw in an audio system, tint the windows, throw on some bigger rims and stop there...

BTW, since I'm on that subject, how big of wheels can you fit on a 250. I'd like to throw on 17's atleast with lower profile tires. Is that possible?

psfred · #29 03-16-2003, 10:31 PM

Two things on the wheels: Offset and overall diameter.

You can put 17s on with low profile tires provided you keep the factory offset and the outside of the tire is the same width and diameter, shouldn't be a problem.

The offset on the W114/W115/W123 chassis is less than the later models, usually more than US or Japanese cars. You will have to check this yourself, the tire shop usually doesn't know beans about it. If you get it wrong, it won't handle properly.

As for the sound system: If you do not have rear shelf speakers now, there are perfs in the cover and knockouts in the rear shelf sheetmetal for speakers. They are fairly small, but the vent duct runs underneath, so if you take it to the "Dr. Dashboard" type places, they will take a power saw to the ductwork, and the air from the trunk gets sucked into the car. Use box type speakers on top of the shelf, the knockout is big enough for the magnets, and there is a notch for the wires. The knockouts are underneath the asphalt sheet, locate them from the perfs on the shelf cover.

If you are replacing the rear shelf speakers, stick with box mounts for the same reasons.

You need to remove the rear seat backrest to remove the rear shelf cover. Two nuts down low by the door and two in the trunk.

Peter

#30 03-16-2003, 10:44 PM

Yea I noticed after looking in the trunk under the rear package tray shelf that installing some speakers would not be as easy as I thought. I would ::LIKE:: to do the cut out route and install some 6 by 9's back there, but I know it won't be that easy and I will have to do a lot of modifying. maybe I could make some kind of cover to prevent all the air from the trunk running in I dunno I'll have to look into this matter more. If I do it I'll do it myself for sure I don't trust those places for reasons like you mentioned lol...