Hello everyone,

I’d like to share my build that has been in the works for a long time. My car that I’ve owned for 27 years have gone through several iterations throughout the years. As you can see it already has been kitted with an all authentic AMG body kit, steering wheel, cluster suspension etc. However, the power of the euro M117, even with AMG cams with solid lifters, and an authentic 5speed manual was just not up to par with the looks of the car.

So I wanted to build my OWN version of a crazy period car, just what AMG, or Renntech would have built back in the ‘80s, if the mighty M120 would have been around.

The ONLY engine that could possibly do is the M120 V12. While I was aware that there were a few documented M120 swaps into W and C126s, I knew that none was mated to a manual transmission. I chose the ZF GS6-53BZ 6speed manual out of a BMW 335i. I chose this, over the many versions of Tremec transmissions, to give the car a more “German” feel, over the more direct, notchy feel of the Tremec.

My number one priority and vision for this build was to keep everything as original and OEM looking as possible. Blingy hardware, haphazardly ran hoses and wires were not going to be acceptable. Also, serviceability was imperative.

I was set on keeping ALL creature comforts that make a Mercedes a Mercedes. I currently have ice cold A/C, cruise control, ABS, ASR, etc.

So as far as the details of the swap, here it goes:

The engine fits pretty much without any mods. I did do custom motor mount arms on the block itself, but retained the OE rubber mounts that have been reinforced. The secondary firewall has been “massaged” to an unnoticeable amount. The battery has been relocated to the trunk. In its place now resides the “coffin box” original to the W140 that houses all the ECUs. The braking system has been swapped over in it’s entirety from the W140 to allow for the Cruise and ASR functions. As an added benefit, I currently have a four channel ABS instead of the original three channel, originally found in all W126s. As a previous upgrade, I have designed custom brackets for four piston Brembo calipers that squeeze on E55 rotors.

And for the Piece de Resistance, the transmission:
Not wanting to use an adapter plate, and having a bad 722.3 automatic transmission at my disposal, it just made sense to make one out of the two. The bell housing part got cut off of both, and after careful measurements it was welded together using an intermediate spacing/centering ring.
This part of the build was made possible by the generous help of my awesome work place, Renntech Inc, in sunny South Florida.

The transmission fits inside the transmission tunnel of the W/C126, with very minor clearancing in the front upper area of the tunnel.

Having already had a manual transmission in my car, the pedal assembly was not an issue. That is a direct fit btw, from any manual equipped W126.

The driveshaft was also custom built in-house at Renntech.

As for the end result, and driving impressions:

Being fortunate enough to own nothing but M120 powered cars, all different generations and body styles, I can say with conviction, this is like no other. Period.

My C140s are reasonably fast, quiet, but sedate and stately.
My SL is quick, and also quiet.
The C126 is totally analog. It feels like a C126, but with balls unlike even a 6.0 4valve. Way quicker. (I know, we work on them, and build them on the daily). Yet when I take the family out, and want to slow down, I can drive around in air conditioned comfort, just like in any vintage Mercedes.

The C126 is about 1000lbs lighter than the donor W140. Coupled with a manual transmission, and 3:06 differential, it accelerates diabolically through every gear. The most exhilarating feeling is stepping on it at 90mph, and getting thrusted into the seat all the way to 120mph. It’s addicting. Just nuts.
It’s a great feeling to know that you’ve built something special, unique, and one of one in the world.

I would like to give special thanks to Renntech for allowing me to do a lot of the work after hours. Thank you Hartmut Feyhl! Also this couldn’t have been possible without the help of my very talented and generous friends, Bret Clemenzi, Danny Rowland, Christian Ramos, and many others.

 

Nice good to see your on the road. The manual trans is a nice touch.

 

Wow, incredible build. For sure looks very OEM. Great job, im sure it helped you work at Renntech.

Ive been looking to manual swap my 94 SL600 with M120. Looks like no matter what it will be an expensive and/or difficult job. Yours looks great!

 

It does help to work at Renntech, for obvious reasons. However this was entirely my own concoction from start to finish.

 

Your username is perfect representation of this car. Fantastic!

 

It's so pretty too.

 

Me looking at that underhood:

Amazing! Great work

 

That’s really well done and very impressive as well. One for the ages

 

Thank you. I appreciate it. It took about a year and a half from start to finish, and I learned a lot along the way. When getting close, I kept promising myself, that I’ll never do anything this crazy again. But now, that I’ve been daily driving this for the past few months, I can’t wait to break that promise! Just waiting for the right opportune moment.

 

Congrats, love it. It’s amazing how much of the engine bay that beast of an engine consumes. Makes you wonder how it fits in the 129.

 

Thank you Brento. Your build is also very beautiful and inspiring.
Just like in any setting, though, the M120 looks very intimidating at first sight, until you remove the air boxes. That opens up a LOT of space to do service.

 

Wow, this looks even better than m113 swapped cars that were just displayed at legends of the autobahn yesterday.

Is there any chance renntech will offer this conversion?

 

I don’t think there’s a “better or worse” way too ok look at these. The M113s, and M113Ks are fantastic engines. Very robust abs tunable lumps. Best I’d all, they’re easily adapted to manual transmission duty.
The reason I chose the M120, is simply I wanted to relive that ‘80s feeling of excess, with the wow factor of the manual transmission. Something that presumably would have been done back in the day, had the M120 been around.

 

this is wonderful. Love it

are those pentas 17 inch versions?

 

Yessir. They are none of the best purchases I’ve made for my car. I was debating to go with original staggered 8/9” Pentas, but I’m glad I didn’t. These totally fit the car both in terms of looks and function. They’re 8.5/9.5 17”

 

Beautiful. And totally unique. Lucky you.

 

Thank you sir

 

This is such an awesome build.
I can only dream of having a manual trans, let alone a 6 speed I'm my W126, which at this time has been sitting in the barn for nearly 8 years now.
Props to you sir for doing such a awesome conversion.

 

Thank you.
I thought having an AMG tribute car with a 5speed manual was a non plus ultra. Until this one! Being able to daily drive it makes me pinch myself every day.

 

Thanks for sharing and appreciate the insight and background.
I had no idea that you worked for RennTech...I would be in trouble if I worked there! Amazing.

Your car is incredible and inspiring, the build is to the highest degree. Well thought out, engineered and executed.

Yasin

 

Thanks Yasin. It is nice having fun at work. I did, and continue to gain experience and knowledge every day.

 

This is, quite possibly, the nicest SEC build I've ever seen. I love the effort to keep it OEM/"Authentic" looking while still turning it into a beast! Hats off to you, that car is nuts!

 

Wow, incredible!

The ecu box really does fit perfectly in the old battery compartment.

What brand of cats are those?

 

The cats are Renntech proprietary units, custom fabbed with offset cones to fit into the cavity under the heat shield.

 

Amazing installation. I'm guessing the LH-SFI engine was easier to integrate vs the later ME with DAS and other headaches.

What company fabricated the custom radiator? Is cooling ok in hot Florida summers? Looks super tight up front!

👀

 

Amazing installation. I'm guessing the LH-SFI engine was easier to integrate vs the later ME with DAS and other headaches.

What company fabricated the custom radiator? Is cooling ok in hot Florida summers? Looks super tight up front!

👀

Yes, working with the LH system has its advantages, but it’s negligible. The benefit of the ME management’s tuneabilty is tempting. I’ve learned this during the S76R build.
The radiator is a generic aluminum unit, with the appropriate dimensions, and In and Outlets. Even so the outlets were cut and modified in-house to fit the application.
You may notice in the full overhead shot, that that picture shows electric fans with no shroud. This setup worked ok, but temps started creeping up in standing traffic with the AC on. The lack of space prohibited fabbing a shroud for this application.
I ended up going back to the viscous fan setup with my own shroud design. The result is Ice cold AC with 89-95* temps on these crazy Florida days.

 

your one of the few members here that has been registered longer than I.

so when do we get driving and walk around videos.

Now if it sounded like the crazy f1 v12 that has been created with that japanese exhaust that would be nuts

Any thoughts on this from Stephen at Curated or the Patina boys. I know they visit RT

 

your one of the few members here that has been registered longer than I.

so when do we get driving and walk around videos.

Now if it sounded like the crazy f1 v12 that has been created with that japanese exhaust that would be nuts

Any thoughts on this from Stephen at Curated or the Patina boys. I know they visit RT

We do a lot of work for those guys, and I see them at the shop frequently. They are not (I guess until now) aware of this project, as I did it at home in my shop.

 

@roadhouse over the years has had many interesting, helpful and good posts, but this one is brilliant. One of these days, with fair warning, I'll drive down to Stuart to see this beauty first hand, with fair warning. Easy for me, I'm only and hour away. but, wouldn't it be nice to have a parking lot meet up someday?

 

I did know you’re in Stuart from previous posts. Stop by and I’ll show you around.

 

Looks like you retained the W126 prop shaft? How does its diameter compare to the M120 cars?

 

One of the beauties of the M120 conversion in these cars is that MB did not strengthen much going from the M117 to M120. The driveshaft uses the same tube diameter and wall thickness. Differential, while allegedly called (strengthened) is still the same diameter ring gear. Splines and CV joints on the axles are the same, although you will notice a more precision and tighter spline fit in the later cars. Wheel studs are the same 12mm 112mm bolt circle. The most noticeable difference is 4 web flange on the drive shaft, which MB abandoned in later years for the original 3 web with a thicker flex joint. Bottom line with the M120 engine, you are not over taxing the drive line. This is a major consideration one should think about when selecting and engine. When the M113K came out, all the drive line components changed. Larger drive shafts with bigger splines and wheel bolt circles.

 

Correct they moved up to 14mm bolts but same 5x112 bolt pattern that’s why all Mercedes rims fit any Mercedes

 

Really nice exhaust work. I found exhaust to be the hardest part. The V12 emblem on the shifter is a nice touch. It seams Mercedes did away with the V12 emblem on the shifters. My 99 SL600 doesn't have it.

 

Easy. The w126 has no subframe in the front. I can take photos next time the car is on the lift.