DIY 1M Exhasut conversion

[uberschnell]

Just sharing some of the work I’ve done. I am going for the full conversion like others, the only difference is I’m planning on DIY, except for painting. In order to do the rear conversion you need to address the exhaust section first. Two choices, custom exhaust set up to fit the new exhaust tip locations or a full 1m conversion. I’m trying to make the conversion as OEM as possible so I went for the full conversion.

Now, I’m also trying to do this as cheaply as possible, so where I can I’m doing my own work and modification. I spent over 10 years in the aviation industry so I’m a decently competent mechanic and own a fair number of tools (including a welder) (note, I’m definitely on the beginner side of the welding scale).

Parts
51488051598 Shield
51718051597 Pan
16137845193 vent pipe
16137845195 vent pipe
16137845194 Exhaust steam pipe with filter
61129217036 pos lead plus pole
61127845120 neg lead
61126929715 pos lead
51128051589 rear bumper carrier

(Big thanks to Phil and Reeves for helping me with the parts )


First, Battery Tray. Here is where the problems start.

The battery on my 135 seems to be significantly larger then the 1m battery. The mounting holes just don’t line up.



So my solution was to buy a smaller battery. I picked up an Interstate Megatron plus MTP-48/H6. Same CCA as the OEM, AH 70 vs. 90 on the stock. Nice bonus, it’s about 23lbs lighter also.



Next problem. The terminal placement with the new batt location is too far away for the existing batt cables. You can purchase the 2 1m cables going to the pos terminal which are long enough. The problem is the ground and the 2nd large pos cable that snake towards the rear of the car. They are both too short for the new batt location also.



That 2nd pos lead runs all the way to the front of the car, no way you are replacing that. The negative cable terminates just under the molding, but the 1m cable does not have the 2 additional leads coming off the connector, so it wont work anyways (if your car is set up like mine). Now, I did notice slack between the mounting points on the long cable. I cut the wire bundles loose between the mounting points in the trunk, removed the slack and re-secured using BMW lacing tape. That bought me around 4”.

Next I welded up a simple mounting jig and moved the battery towards the right as far as I could.





The resulted in a few things. One, I no longer needed new pos battery cables (saving me at least $200), and the long pos cable now reached the terminal. For the negative cable I had no choice but to butt-splice. Picked up a 0 gauge butt-splice kit and welded the bottom half of the 1m cable to the top half of the stock cable. Results, all fits now like it should.

You can see below how it would look if you did not extend the cables versus the proper fit.





The tray just drops and bolts in, shield just screws on, simple.

Next, Charcoal Canister relocation.

Pretty straight forward. You jack the car up and remove your right rear wheel and well cover to do this. The amount of work is fairly high. The lines you are replacing are straight forward, snap on. You will need to access the fuel tank through your rear seat. I suggest you do this with the tank almost empty. I imagine (not totally sure) you could find a way to twist/stretch(?) the stock lines to fit but I’m pretty sure you will kink something and end up with codes. Regardless, my goal is to not short cut this convo so I replaced them all which took up the better part of the day.

Next issue: the electrical lead to the canister is too short for the new location. So, to solve this I had to extend the cables. Using environmental splices I extended the cable about 8” and re-routed the line. Worked perfectly.





Next, Exhaust mounting set up.

Again, very straight forward. All you will need is the 1m rear bumper carrier as it has the two rear exhaust hangers attached to it. You will have to remove your rear bumper cover. Its 4 bolts for the carrier. In order to save $200, I picked up a couple of 90 degree exhaust hangers and welded them onto my stock carrier.




You can now fit any of the 1m exhausts out there. Since I’m planning on doing the rear conversion later this year I chopped up my diffuser as a temp solution (doesn’t look too bad for a temp solution).

Plan on taking at least a full day to do this, and a 2nd set of hands is certainly helpful for the tank drop.

As for sound, the 1m exhaust is deeper and slightly louder. Keep in mind the 135 mids have a true working resonator and it’s been shown the 1m mids have a non-resonated y pipe under the pseudo resonator cover (crazy, don’t ask me why) so the sound is a little bit more tamed then a stock 1m, but nice nonetheless.

Good luck if you want to do it, and plan on waiting a few weeks for the parts as they have to be shipped in from Germany.

[1&done]

Nicely done! Did the new battery require any coding?

[uberschnell]

Yes, I took it to the shop and they coded it to 70 ah for $20. Took 5 minutes.