Interesting hot rod project idea - Mercedes Meets Nissan

[NeufUnSix]

My father and I have been restoring a Mercedes 250C coupe for many years. It's been fun, but I've always dreamed of a V8 stuffed into the engine bay to replace the dull iron block six that resides there. On top of that the transmission isn't in great shape. I'd pondered it for a while - get a cheap Mercedes S-class, rip out the V8 and tranny and stuff it in. It's been done before, and it's a better option that the typical small-block conversion (much, much lighter, lighter than the six, and nice free-revving power). But I never pursued the idea; besides, most North American Benz V8s from the 80s struggle to break 200 hp, even the monster 5.6 is only rated at 250 hp.

Last year I bought a 1991 Infiniti Q45. It was my winter beater, I paid next to nothing for it and it the engine is in fantastic shape. I'm now trying to get rid of it, but interest is nill. I guess 8 mpg luxo barges aren't popular on the market at the moment. Then my dad proposed an idea - why not part out the car and keep the engine and drivetrain to stuff into the Mercedes?

Suddenly the hot rod project is possible, with the engine and transmission at hand. The 4.5L in the Infiniti is an alloy block, four cam, variable valve timing design with rock-solid internals - and it's compact and light. On top of that it makes something around 300 hp and 300 lb/ft. It makes a load of torque and a great top end rush right up to 7000 rpm. In a two ton Q it flings the car to 60 in 7 seconds. The Benz weighs about 1000 lbs LESS, including the iron block six. That is a recipe for fun.

Now we just have to start working out logistics - making sure the thing actually fits into the engine bay, figure out how to mate a Nissan transmission to a Mercedes driveline, work out what electronics we need to tear out of the Q and how to bypass the bits we don't need. Then the real fun begins.

[Oldfisti]

 

[lethe]

Sounds like a fun project, keep us in the loop. 

[Bun-bun]

You'll need to cut /replace the driveshaft and match the transmission output yoke, and the rear end input shaft. I expect this means a custom built driveshaft.
The Infinity is  fuel injected, so you'll need to transfer the PCM and associated wiring to the mercedes.
You will need to fabricate new engine/trans mounts, and may need to make mounts to relocate the mounting points on the mercedes. The mounts may have to move transversely as well as laterally.
You will probably have to fab new shift linkages to get the mercedes shift lever to operate the infinity trans.

Good luck, and don't forget the pics!

[Speeddog]

How robust is the Benz rear end/ ring & pinion?

[NeufUnSix]

Not sure about the rear end strength. W114s had a specific differential for models up to 2.8L, V8 models had another (with LSD as an option). I know the transmission is rated to 250 lb/ft max, so it wouldn't be a stretch to imagine the rear end has similar limits. The real question is what is interchangeable, the easy route would be to get a beefy diff off a junk SEL/SEC/SL and call it a day. It's a shame I won't be able to use the Nissan final drive, it's the same LSD as a 300ZX and is pretty effective.

My main concern, aside from actually fitting the engine, is the mating of the transmission to the driveshaft. New engine mounts are easy to fabricate, and the engine bay is huge so there should be room. As mentioned it will need a customized driveshaft, assuming there is room for the tranny at all. These are the logistics that we need to start working out on paper before we rip the engines out.

Electricals are easy, in theory. Just need the ECU and TCU and associated sensors, bypassing redundant systems with resistors if they cause problems when disconnected. The main work is tracing the wiring and removing everything without damaging or mixing anything up.

[Speeddog]

Skinny tires can help limit load on the rear end. 

What's the word on the street about rear end durability with a small-block?

Assuming the trans from the Q45 is an automatic?

A little more cutting and fitting and you *could* use the Q45 final drive. 

<threadjack>
Do you know what a dilapidated '74 280C is worth?
</threadjack>

[silentbob]

The drive shaft is easy.  When I stuffed a Richmond 6 speed into my Jag convertible I just brought the old drives haft with the front yoke for the Richmond down to the drive shaft shop along with the final length.  They had a new aluminum drive shaft made up later that week for a couple of hundred dollars.

[Rameses]

Several years ago I was contemplating dropping a built SBC into a '78 Mercedes coupe.

I was talking about putting a 'Vette rear end in it to maintain the independent suspension.

An individual whom I trusted very much on the subject said "no need.  Mercedes rear ends back then were WAY over-built."

He did advise changing out the axle shafts in favor of a beefier option though.

And if your driveline has flex-discs I'd ditch those for u-joints when you replace the driveshaft.   

[MendoDave]

 

[the_Journeyman]

This sounds like a fun project!

JM

[Duck-Stew]

+1 on the driveshaft comments.  Usually $200-$400 will net you the desired shaft all balanced and ready to go.

+1 on the skinny tire comment for torque limitations on the diff, but hard launches become tire-smoking-exercises real quick.

+1 on the 'dare to be different' chalkboard.

--and lastly--

+1 

[derby]

+1 on the skinny tire comment for torque limitations on the diff, but hard launches become tire-smoking-exercises real quick.

...what's wrong w/ smokin' tires? 

[derby]

--and lastly--

+1 

[NeufUnSix]

74 280C isn't worth a lot. Ours (72 W114 with 2.8L twin carb) is worth MAYBE 7K, if someone were willing to pay that (not many are), and it's considered more collectible than the later models (probably because it is prettier). We've invested over 15K in restoration. In other words, we will be keeping it for a while. We paid 1500 for it originally, and that was probably too much.

Not sure if it has flex discs. I swapped out the driveshaft years ago and I don't recall anything other than a beefy driveshaft on U-joints. I may be wrong. The axles are pretty spindly though, just a thin steel rod on CV joints. They will probably the weak point.

The Q tranny is auto, unfortunately. It's also a mediocre design, if we had unlimited funds I would have it rebuilt with stronger internals, new valving and a performance torque converter. Nissan never made a manual that fit the VH45 (the only car it was ever put into was the Q/President) so that option is out.