I tried MMP Stage 3 twin turbos, but never felt the “wow” factor I was hoping for. After worrying about wastegate rattle and smoking turbos for too long, I decided it was finally time to go big or go home. Meet the Doc Race 135i/335i N54 single turbo kit!
Once I decided to convert my N54 from twin turbos to a single turbo, I spent countless hours researching what kit I should go with, which parts needed to be replaced, what upgrades needed to be done, etc.
To save you that same hassle, I will share all the information you need to know below. With this complete list, I was able to safely make 749whp on the stock motor in my BMW 135i. Even if you’re not after a ton of horsepower, this is a great kit to go with when getting rid of the stock turbos.
I want to kick off this post with a reminder that I’m installing the Doc Race single turbo kit outside of the car on an engine stand. Part of the reason I bought this kit was because I blew my motor which required to me remove and re-install a new motor. Great excuse to upgrade… right?!
The kit showed up about 4 weeks after I ordered it and came complete. I didn’t want to gamble with other vendors’ long lead times and kits that arrived with missing or poor-fitting parts. Doc Race knocked it out of the park and I’m glad I chose their kit!
Everything looked beautiful. I opted for the ceramic coating option and a ball-bearing 6266 turbo. The kit includes almost everything you need to convert to single turbo! Now let’s get these beautiful pieces where they belong…
Manifold studs replaced, manifold, heat shield and water pipe installed.
Walnut blasting is one of the most common maintenance tasks for the N54 engine to remove carbon buildup from the intake valves. Some shops or dealerships charge an arm and a leg for this service, but it can be done at home for much less!
After “sending it” at 30psi for a couple hundred miles, I developed a misfire. I narrowed it down to cylinder 3, but wasn’t sure if it was plugs, coils, injectors, etc. I swapped all accessories between cylinders, but nothing would follow. That’s when I started to get worried.
Without wasting any more time, I busted out the compression tester. The results were disappointing.
I’m not sure what exactly caused the problem, but adding a tablespoon of oil down the cylinder boosted compression back up. 99% sure it is a cracked ring or a chipped ringland. If I had to guess, the car developed a misfire but I was too greedy and stayed on the throttle while it was a misfiring for a couple pulls. Or maybe it just randomly gave up… I’ll never know why. The logs looked good before the misfire, but I knew I was playing with fire at this power level.
After saving up for a few months, I bought a used motor from a junkyard. It came out of a 2008 335i 6MT with 91,223 miles. The car was hit pretty hard on the driver’s side, so I’m not worried about flood damage or anything like that. It was also modified, so I’m hoping it was taken care of by an enthusiast.
2017 Update: This 335is/550i clutch setup held up great for 22k hard miles! I have absolutely no complaints. In June I decided to upgrade to MMP Stage 3 turbos and chase 700whp. I knew this clutch setup wouldn’t hold, so I removed it and replaced it with a SPEC Stage 3+ unit.
After turning up the boost on my stock turbos, the factory clutch started to slip. I decided it was time to upgrade so I could enjoy my 135i to it’s full potential. From SPEC to ACT, there are plenty of aftermarket options available. Then I found the 335is/550i clutch upgrade on ECSTuning, so I started to do some research.
This clutch comes factory in the F10 550i, which puts down 443 tq and weighs a whopping 4552 lbs. DINAN doesn’t offer a clutch upgrade for their different stages of 550i’s, so apparently they feel that it is adequate. Their Stage 3 550i puts down 580 tq and they kept the factory clutch. Also, someone on the forums is using this clutch and claims that it is holding at over 620wtq on aftermarket turbos. To me, it sounds like the clutch is severely underrated.
My 135i won’t see more than 500 tq anytime soon. I’d guess that it is currently around 420whp/465wtq, but only weighs 3300 lbs!
Since I had to remove my intake manifold while walnut blasting my intake valves, I decided it was the perfect time to tap the manifold for a larger vacuum line. TiAL recommends that their blow off valves be connected to 1/4″ vacuum line, not the small factory 1/8″ vacuum line. This is crucial on modified BMW 135i or 335i.
Once you have all of the parts, it’s a pretty straightforward procedure. First, cap off the existing port with a vacuum nipple and a zip tie. I like to leave this nipple untouched in case I were to ever go back to stock, then I can just plug the larger port we’re about to create.
Next you’ll want to find the flat surface next to the old nipple. Then you’ll start drilling a hole with a small drill bit and eventually work your way up to a 1/4″ bit or until the tap can thread into the hole.
Now you’ll use the tap tool to thread the plastic to accept the fitting. Run this tap into the hole until you can thread the fitting in.
Grab the fitting and wrap some teflon tape around the threads. Then carefully thread it in until it is nice and tight.
Lastly, you’ll bust out the epoxy and coat the outside so it won’t leak.
Vacuum or blow out any plastic shavings that are left in the intake manifold and reinstall. Now you’ll grab your new 1/4″ vacuum hose and connect it from the blow off valve to your larger port for ideal operation.
A few weeks ago the car started making a squeaking noise. So, I popped the hood and started taking a video. Here is what I found:
As soon as I noticed the shredding serpentine belt, I drove home and parked the car. Ordered a new belt and tensioner, along with oil filter housing gaskets (#1 & #2) because mine were leaking. Once the parts arrived, I installed everything. Here is a picture of the OFH gaskets going in, what a mess…
Obligatory picture of the shredded belt: I put everything back together and assumed all was good. Wrong. About 50 miles later, the belt started shredding again. This time it started wrapping around the alternator pulley and burnt up the backside of the brand new tensioner pulleys.