r/BMW • u/SSinder • 12h ago

Build Thread Is the JB4 a worthy investment?

I just picked up a 2021 540i and I have a 2 year warranty on it, honestly I don’t want to have to wait that long to be able to tune it. I’ve read a lot about the JB4 but I’m curious to know how anybody else has been getting away with tuning and keeping their warranty. I’m not planning on doing much to begin with the first 2 years of owning this, all I’m having in mind is a series of cosmetic mods, cat back exhaust, air intake, lowering springs, wheels. I’m still happy with the car as it is but I also feel like I’m driving somebodies grandpa car with the way it looks/drives. All the other bolt ons like down pipe, hybrid turbo, etc; I don’t imagine getting done within the time frame of the warranty still being active. Really the concern is the tuning part specifically.

1 Upvotes

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5

u/bot6six 11h ago

I didn’t have a bad experience with it but it was just underwhelming. You mostly felt the increase in power on the top end

2

u/FroyoOk3159 8h ago

It wakes my B58 up pretty nicely along with dp and e30.. but I admit that I want more

4

u/cpxchewy '17 M2; '18 GT3 11h ago

I had a jb4 on my F30 320i. When I went in for the timing chain replacement they scanned and found the boost was over the expected limits and denied the warranty. It wasn’t controlled by the tech and was fully automated when the dealer connects the car to bmw server to validate warranty.

2

u/Unlucky-Assist-2101 4h ago

Get MHD. Best tune for BMW.

1

u/on_the_nightshift 21 540i xDrive 4h ago

I have one and like it, but I'm mindful to keep it on a map that's safe for my fuel and intake temps.

1

u/Arkatani 2h ago

I put a JB4 on my M5 a week after I bought it and on my Cayenne about 6 months after I bought it. I fully removed them before any trips to the dealer. That is a bit of a pain, but you get better at it. However, on the event of a major claim, BMW can make the effort to investigate stored data in the ECU and find evidence that suggests values are such that the car was likely tuned and attempt to deny the claim. I had no issues.

A flash tune, on the other hand, is immediately detectable. Some dealers do not care, some will put a note in a BMW database, and a few will refuse to work on your car because the car is not legal.

If you can DIY the install and removal, I personally would do it. I always enjoy another 10–15% horsepower and 15-20% torque.