2008 BMW 135i Black

‘Dementor’ 600HP BMW 135i Build: First Kill + JB4 Time

Jake Mayock

Meet Jake

Jake currently owns two N54 powered BMW’s – an E60 535i and E82 135i. Jake has 10 years of experience maintaining, repairing, and upgrading his BMW’s. The 135i features a single turbo Precision 6266 conversion capable of 700+whp; Jake completed the entire project on his own. With over 200 automotive articles published, Jake brings a balance of writing skill, hands-on BMW experience, and technical knowledge to the table.

I’m dubbing my 600hp 135i build out “Dementor”. Why? Dementors brought hell to everything in Harry Potter, sucking the souls out of wizards. With 600hp, my 135i is going to bring hell to just about everything else on the road. It might take a little bit of time for it to live up to its name, but I’m about to take it one step closer. One big step, hopefully bringing about ~70hp to the wheels. It is time for my 135i to get the infamous Juice-box “JB4” Tuner. Today, ‘The Dementor’ had its first kill, and it’s hungry for more.

My Thirst for Power

Prior to my 135i, I drove a Mazda RX-8. The car was fun, and different. It had a tiny, naturally aspirated 1.3L Wankel Rotary engine in it, and put out 232hp and 159tq to the crank. To the wheels you’re looking at roughly 180whp, and the torque numbers are abysmal. It was once ranked in the top 10 for “best handling cars under $100k”, but it didn’t have the power to take anyone off the line. I didn’t want to be the guy that was always saying “well my car is faster around the corners, the straight line doesn’t matter”. Maybe you can justify saying that if you are actually going to track your car against your buddy (My fellow RX-8 buddy used to walk vipers around the track) but otherwise, we all know straight line power is what matters in the streets.

I wanted a car that would walk people on the track, and hold its own on the straight line. And the 135i was the answer. I’ve had it for about 5 weeks now, and have enjoyed the hell out of the performance improvement compared to my RX-8. I’ve kept it mostly stock for now, with the exception of DCI’s, so that I could appreciate the stock power before my 600hp build-out. But after today, I’ve decided its time to add some serious power gains. I had my first kill on the streets today (safely), but didn’t embarrass the dude as much as I wanted to.

First Kill: 2017 Mustang V6

Before I get into my story, I was on a three lane road, there was a lane in between the two of us, and the road was clear for half a mile at the front and back. The speed limit was 50mph, and we both eased off at 60mph. I’m one to keep the high speed racing at the track, but there’s no harm in a little off-the-line fun on an empty highway.

If you live in Texas, or have even just visited, you’ve probably realized there are A LOT of two things: (1) trucks, and (2) MUSTANGS. New-age American “muscle” cars are like fast food restaurants down here, there are always 4 in sight no matter where you are or when you’re looking. Typically they are V6 Mustangs, being driven by your average 18-year old fruitcake. So when you see one, and you know your car is faster, you do everything you can to put all their hopes and dreams down the toilet. In this case, you smoke their “muscle” car with a stock-looking BMW.

I linked the heading text to Car and Drivers review of the 2015-2017 V6 Mustang, if you care to read about it. It puts down a pretty impressive 300hp, and 280ft-lbs of torque.

The First Red Light

I was at a standstill at a red light, and this mustang was in my rear view braking for the light. I hadn’t put my 135i to the test yet, or my off-the-line skills with the 6 speed manual, so here was my chance. When the light turned green, he was probably at a 15mph roll or so, and got on the gas hard. I jumped the clutch and took off. He had me easy from his roll, but by the time we let off at 60mph, I was neck and neck with him. More road and he would have been crying.

He Should Have Known What Was Coming

We pull up to the next red light, both thinking to ourselves “I’m gonna show this guy what I got”. Off the line, we both gave it a no-tire-spin launch. I took him in first, and then kept the lead through second, easily. By the time we hit 60mph and let off, I had a car length on him. My first kill. I was proud, but come-on, its a V6 mustang. It was closer than I had expected it to be, and drove away a little disappointed knowing that if it were a V8 mustang, I’d have been toast.

The 135i was definitely one of the faster cars in its class back in 2008, but today things are different. Nowadays you have a stock Hyundai Sonata that will pull a low-5 second 0-60mph. Everything is getting faster. My RX-8 was fast and quick back in 2007 when it came off the production line. But today, a V6 F-150 will beat it in the straights.

Thank God the 135i is insanely tune-able, because I need more power.

Get Ready for the JB4

You probably read the titles of my posts, and then are disappointed because you wanted to see a 600hp 135i. Not a 315hp 135i that is months away from reaching 600hp. But I have to get you a little excited somehow right?

The JB4 is coming very soon. Maybe I will put 400hp in the title of my next post, and it will be realistic.


I will add some links here to the more exciting posts when the time comes (FBO, turbo upgrades, etc.). Until then, subscribe and stay updated on what Zach and I are up to. I promise, you won’t be too bored because we post a lot of tuning guides, and walk you through modifications to help you build your own beast. For now, read our own guide on building a 500hp N54.

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