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Hello everyone! Been off the forum for several weeks as my job has been really time consuming lately.

Last friday I had a chance to drive my boss' show quality AMC AMX SS from 1969. It has the 390 ci engine with 420 BHP. That thing is simply spectacular!! It has a 4 speed manual and a limited slip diff. If you slam the gas in any gear while coasting and it will slip the tires and start drifting.

The only downside is the usual vintage american muscle low reliability (risk of flaming). After a 40 minute drive, the alternator died, killing the battery. We towed it back to the shop and replaced the altenator and battery. After another 30 minute drive, the fuel pump died. So we got back, fixed it and went out again. Only 15 minutes later, the clutch started slipping, so we decided to park it until fixed.

After driving such a particular car, I decided I really need/want a muscle car that is fun to drive, but realiable enough to take it for a drive without needing to have a tow service number in my speed dial...

I looked around for info and it seems putting a M116 or M117 engine in a W123 chassis is a very doable project. The M117 seems to be the best route, however. It's lighter, produces more HP and it might be possible to get performance internals down the road. I also saw some info stating that the bolt pattern of the bell housing is exactly the same as the M110 and the OM617 engine, giving a chance to get a manual transmission behind this engine.

As for the project platform, a coupe W123 is the way to go. It's a great chassis which I'm familiar with, parts are readily available and it's a safe car in case of an accident. Some updates would have to be done, like late W126 front brakes, Bilstein HD shocks, Vogtland springs, 3.46 rear end (to aid the transmission stress and limit top speed) and so...

What do you guys think of such a project? Think of this as a mid-term project to be developed in a 2-3 years span.

Happy driving!

P.S.: I posted this thread in the diesel section because of its high traffic. I'm really looking forward for the members' advice.

Which is the M116 or M117 engine?

Didnt 107 bodies have chassis cracking due to the weight of the 4.5L V8 and the 5.6L V8? Thought I heard that somewhere.

It may be blasphemy, but I think Ive seen GM 350 V8 swaps into w123 cars. Very ommon, and you could get something like a Vette engine with LOTS of HP and modder parts for a decent price...

Just a thought.

Standard US muscle don't have low reliability in my experience.

AMG already did it.

An M119 would be the motor to use.

I know diesel might be better for the sake of the 300D culture, but even thought the knocking noise of a diesel is sweet, I'd love to own a W123 with a deep Merc V8 rumble. Imagine the drone while cruising a 60 mph in fifth gear just slightly pressing the gas... :D Gotta love that!!!

Sounds like a fun project, I believe its been done before and isn't TOO hard, depends how far you want to go with it. One problem with w123s and w126s in terms of performance is their tires are pretty skinny and due to the suspension design you can't fit much bigger/wider wheels and tires without modification--but obviously keeping it stock is out the window so you've got options. I've had trouble getting my w126 to hook in the rain, and usually chirps the shift to second gear in the dry so you'll want to keep that in mind for your budget.

There are a couple of factory LWB 123s on eBay at the moment, both with 116/7s.

Another problem is sending that much torque through available 123 diff ratios and axles. You might have to fabricate attachments for a Dana 44. In that case, go with an American V8.

Sixto
87 300D

I totally agree with the tires width as being a problem in putting all the power down to the ground. However, having this limitation might be a good thing, as the tires will work as a power fuse.

As Sixto said, the torque of the engine might kill the diff and the tranny in a W123. But, if you think about it, the powertrain of a 280E, for example, can withstand revving up the engine and letting the clutch go to chirp the tires and do a burnout without breaking anything. Even if you get a lot more power from the M117 engine, the tires will slip way before anything breaks. That's kind of an advantage of having the tire width limitation... IMHO

So it seems this project requires a a donor second gen 560 SEC/SE/SEL and a coupe W123, preferably a gas powered one, such as a 230E or a 280E. The W126 will provide the engine and tranny (if the manual swap is not doable), front brakes and perhaps some parts of the wiring harness and other hardware. The W123 will serve as the mounting platform. AFAIK, some additional parts will be required, such as a 617.952 radiator (to keep the beast cool).

Now, the legandary question, which came first: the egg or the hen? Should I look for the donor, to pull out the engine and tranny for an overhaul? Or should I look for the W123, disassemble it, do all the body/paint/rust related work and reassemble it first? I'm thinking of this project as a lifetime keeper. If I decide to jump into this, I'll go for the whole deal... You know, new paint, new upholstery, new everything. I've always dreamed of having a 0 mile, brand new W123, so I'm planning on making this as close as it gets...

Might be easier to start with a 124 coupe or cabrio (no factory 123 cabrio) and upgrade to M119 power. A lot more plug-n-play bits in wrecking yards (big brake upgrades, etc.) and a suspension that can handle the power.

Sixto
87 300D

We were discussing at one point just what it would take to drop a Ford 8.8 in the rear end. Lots of gearing and posi options and while you're doing all that work anyway, narrow away. Here's some food for thought: http://www.peachparts.com/shopforum/2626411-post26.html

I had an eighty four one twenty six coupe with the five liter aluminum v eight. The coupe was a bit heavier than a one twenty three but still was marvelous to drive with lazy torque always on tap. Swap the engine tranny and diff and you would have a pretty nice pacakge. Of course the five point six is the same basic engine and the euro version of it has lots more power but the five point six and the euro take premium while my five liter was content with rug.

It all will more or less bolt in with minor mods I believe.

I believe the exhaust manifolds will interfere with the inner fenders though. Headers might be needed.

I would put up a 60's American car that is driven on a regular basis against a m116/m117 any day. In my experience, many failures on older cars come from letting them sit, ie gaskets, hoses, fuel pump diaphram, etc. And the American engine will be much less expensive for parts and service, and easier to work on yourself.

I really like the W123 better over the W124 and being a W123 owner for several years, I'd like to stay in that road...

Perhaps a Ford diff might be a good option, but if some customization has to be done, I rather use a Mercedes diff to stay on the purist side. Perhaps a W126 diff with the proper gear ratio such a 3.46, which gives you excellent off-the-line performance while limiting the top speed a bit to stay within the W123 speed capabilities. IMHO.

Regarding the interference with the inner fenders, I've come to several wonderings on this subject. I've read that the M116 is a narrow V8 and it is full 2" narrower than the M117. It was available in 3.5, 3.8 and 4.2 liters, while the M117 was available in 4.5, 5.0 and 5.6 liters. Some of the early M116 were cast iron, while the later model are alloy. Also, both the M116 and the M117 share a lot of internal, such as conn rods, bearings, fuel injection system, etc. Being the M116 narrower and presumably more convenient for this project, would it be possible to fit larger pistons to increase the displacement to brind it on par to the M117? That would provide the best of both worlds: higher output in a smaller package... Just brainstorming...