Blasphemy: W126 in 21st Century Edition - Viability

[Irresistance]

Hi there all,
Been away from this forum for a while... all cars are still spinning along happily, though we sold the W210 wagon, moved house and I have found myself to be in need of a new vehicle.

The W220 320 CDI just hit 300.000KM and I am hapopy to report that (in Germany) I managed to speed it up to 241KM/h which is kind of strange coz supposedly it only does 230... (and yes, 241 on the GPS )

But - to the topic at hand.

I have decided that I want a W126 with a modern engine and interior... something like the 5L V8 out of a W220... maybe from the W140 though that would be sub-optimal. I am suspecting here that a more modern engine (W221, W211, etc.) would be too complex to implement given electronics and all, but I am happy to be proven wrong.

I love the W126 body the most of all mercs, but I can't deal with its 'default' gas mileage; something more modern is required. I am not going to put LPG in it, and I want it to be a decent beast, capable safely of 250 KM/h on 1000+ mile journey without so much as a sweat. Aside of engine and gearbox, I also plan to give the interior a serious upgrade, not to mention the suspension and braking system.

So - question is: Does anyone of you have any experience or knowledge of what kind of max upgrade is possible in a W126. Cash is not limitless, but I am willing to spend non-trivial money on this with the aim of having a car that can survive 100000 miles/5 years without a problem. In an ideal world I'd get a spotless W126 500SE 1990 body with all possible gizmos, gut the engine, gearbox and diff and replace it with a W220-era combo. The outside of the car is to remain unchanged - no bulges on the hood, no vents, nothing. It must look like a normal W126 500SE.

And yes, I am fully aware that doing this is "wrong" and I fully respect the opinion of those who think it is nothing short of a blasphemy... in fact, I almost agree. But it is truly impractical to live with W126 gas mileage in this day and age, and I need to find a way to blend the eighties with 21st century tech Any help, suggestion or tips very welcome!

P.S. Only gasoline engine are going to be considered; done with Diesel

 

[ZZZZ]

No idea how to implement it, but I must say - not blasphemy at all: my ideal car would be old shape body (W111) with modern interior and engine

 

[LostKiwi]

What makes you think a 140 era V8 (m119) would be worse than a 220 era m113?
The m119 is generally thought to be one of (if not the) finest engine ever made by MB.
Strong, reliable and actually more powerful than the later engine too.

 

[Craiglxviii]

Just 45kg heavier

 

[Irresistance]

Right - had a quick look at it... indeed the M113 has 14 HP less, and interestingly even seems to have a slightly worse gas mileage than the W140 M119 engine. The only thing that I see as a potential issue is the gearbox however - it appears the M119 was available with a 5-gear box but I suspect it may be tough to find that particular combination. Willing to give it a go, however.

I'll be honest though I haven't got the foggiest idea as to how viable such DIY upgrades are - what kind of issues can one expect when replacing the core guts of the car? I imagine that one will need to create new engine mount points, gearbox attachments and so on..? Of course, I will not be McGuyvering this together myself, and will employ my venerable mechanic to do it, but I am curious just how much of a hassle this will end up being.

Having had a look at eBay Germany it appears there are many versions of the engine... W124, one out of an SL500... I imagine the W124 version will be most 'fitting'... though I can't seem to get info on the type of gearbox. Would an engine that has been used with a 4-gear box work fine with a 5-gear 722.6? Or will that just send the ECU into a world of confusion? Just how amenable to alterations/re-programming are these components?

 

[d215yq]

If it's just gas mileage, assuming you get 27mpg (optimistic) out of a newer 500 that's 17000 litres in 100,000 miles. Assuming the original 500 would get 22mpg (optimistic) so that would be 20000 litres in 100,000 miles; my experience is the newer the car the less they get their official figures and cruising there won't be much in it as the modern stuff is more efficient at idle/around town etc. .

So that's about €4k more in fuel (probably a lot less) for the original. Can you really modify it all for 4k?

 

[LostKiwi]

The 5 speed M119 variant isn't a 722.6 - its essentially an 722.4 with an electronically controlled 5th gear 'bolted on' (and called a 722.5). The rest of the box is pretty much pure hydraulic.
I would imagine this variant may be hard to source but should be relatively easy to adapt into working with the rest of the car. It will also both straight up to the M119 (which may not bolt to the 722.6 very easily).

If you get a pre 1993 M119 it will have 326hp against the 302hp of the M113.

The M119 is beautifully engineered internally with such goodies as forged conrods from standard, 4 valves per cylinder (3 in the M113) dual overhead camshafts per bank and variable valve timing (the M113 isn't VVT and only has a single camshaft per bank).
In my opinion it should be far easier to adapt an M119 and 722.5 into a 126 than the M113 and 722.6 (the 722.5 was used in the 126 as well so if you found a 5 speed W126 you're halfway there).

 

[Irresistance]

Right - that's the info I was very much hoping to find, thank you Sir Lo and behold, there actually is indeed a 722.5 for sale her in my region, though from a 3.2 engine. I like the idea a lot, especially since it is a rarer and unusual part, the kind of thing I am naturally fond of

I did wonder why 722.4 went to 722.6 - I guess now I know it didn't And I agree, this is a far more agreeable combination to use. The hunt is on, I guess... thanks again

 

[LostKiwi]

As the gearbox is hydraulic you may have to do some work on the valvebody to get the shift points right. The 6 cylinder engines will rev much higher than the V8 (7k vs 6k). Not sure about the torque handling capability of the 6 cylinder variants either.

 

[LostKiwi]

You may find this helpful:

 

[brianbrian]

Gen dobre Irresistance, I put a diesel into a 129 eight years ago, still have it, and over the moon with it 40mpg.