Hello everyone,
These MBWorld forumns have been my home for many many years and I’m hoping they can pull through one more time for me. I have rebuilt many crashed Mercedes and done every possible service on my 2012 C300, formally my dad’s daily driver for 7 years and over 200,000 miles. I’m 20 and live in New England, about 2 years ago my dad and I were involved in an accident in our c300, we were t-boned by a semi truck that ran a red light. The car was totaled but she did her job and we both walked away with only minor dings and dents, couldn’t say the same for the car, the passenger side was pushed in about a foot right at the main front/ rear door pillar. We bought the car back from auction for dirt cheap to save some parts we had put on together, as I tore it apart one thing turned into another and 5 months later we had fully rebuilt the car ourselves with all oem parts and to factory specs. Not even a full dealer of Mercedes techs could find an issue with it when we were done and she is now better than ever, we swapped the engine to the 3.5L M272 and it’s been great. It was always my dads dream to build this car into a street car with me and now I’m calling for help. I am very comfortable with modifying cars, fabricating, welding and electronics just as some background. My Dad was diagnosed with grade 3 brain cancer last week and he is going to fight it with all he’s got but I want to build this car with him while I still can, god forgiving. I want to be able to keep this car till the end of time as a memory of him whether he gets to enjoy it with me or he gets to enjoy it from up above. I plan to swap an ls3 v8 into it mated to a t56 manual trans running off the pre facelift manual c300 clutch assembly. I plan on contacting Texas speed this week for some help. I know I will need to modify engine mounts to weld up to the subframe and modify the trans mount and trans linkage to accept a manual trans. I plan on doing fuel pump and line upgrades, maybe a fuel line return if needed. A ford 9in rear end with custom axles and driveshaft, w204 c63 brakes. Front axle delete, leaving the axle cups bolted to the hubs for wheel speed sensing, bc racing coil overs and a custom radiator and fan setup. With custom power steering lines and a/c line sic the compressor will fit. This is not the part that scares me, I really need help with ecu and how I can retain as many factory gauges and speedometer as possible. I know I left a lot of plans out of here but this post was already long enough, will answer more down below. Thank you for reading and any guidance you may have. Please don’t flood the comments with why bother, it’s not possible, just buy a c63, etc. This is going to either be a final send off for my Dad or it will be the project we will drive till the end. Thanks for the help ✌️

 

First, I'm sorry that your dad has stage 3 brain cancer. I hope you have a good time doing this together.

I think you may need a stand-alone engine management system. I'm guessing, but because these cars have temperamental electronics, I'm not sure how you would control fueling and spark on a V8 with a unit designed for a V6, not to mention all the other engine control sensors. Also, converting from an automatic to a manual transmission is going to be a challenge, assuming you can find pedals to fit the car. Having done an auto to manual conversion on a 1999 Audi A4, it was a pain and that was with a transmission made for the car.

What is your goal? Are you trying to create a sleeper street car, or is it more for the strip?

I'm not going to say this is impossible, but it is going to take money and time to do it.

 

Sorry to hear bro. I don't have any useful info on the LS end, but perhaps you already know, you can swap the M273 5.5 in and most of the items are bolt in. I would get some headers on it, and you should be able to use the c300 manual trans as well.

 

reply: thanks for the condolence man, definetly plan on running a stand-alone, thinking a Holley dominator since it will be plug and play with the ls platform. Trans wiring to get it to work with the reverse light shouldn’t be too bad. I happen to already have a spare pedal assembly from a w204 manual c300 so I should be good there. I plan on locating the battery to the trunk to free up some room in the engine bay for wire passages under the air box to the cabin and for a space for the ecu. The goal it to just make a bad *** sleeper street car. I have some front c63 bucket seats in my basement so those will be nice. I think I’ll be good in getting of the mechanics to work, I’m just curious to see if anyone has any insight on how I may be able to retain factory gauges like the speedo, etc or if I can somehow just leave sensors plugged into the stock harness so that the factory ignition key will work even though the starter will be hooked up to the ls motor. If I can somehow retain the factory ecu it would be great because I’m my state they do an obd2 test for state inspection which is just a check of the cars monitors to see if any of them are failed in the ecu checks. Any thoughts on that?

 

definetly curious to hear about this more, what type of ecu, electronics are required for this swap. Has anyone turbo’d this motor, I imagine it’s been supercharged before