[Tiberius73]

I have bought an N54 with a ton of miles and a ton of issues. I've worked through most issues (suspension, dead HPFP, VANOS issues, ...) and the car is running and driving.

The old turbos were BMW OEM and put out ~16-17psi, but whined a lot, especially when cold and had nasty, nasty, wastegate rattle. But power was smooth if you put your foot down from 2000rpm right up to redline. But the turbos had to go as both impellers had many chipped blades as well. I shopped around for "bang-for-buck" as this is a project car, a beater or whatever you want to call it and I don't want to go for 700whp and all the costs associated with this.

Thge new turbos are new, they are original frame, and with a forged billet wheels on a 6x6 blade design. Airflow should be around 15-20% more than stock. The wastegates are also looking like the new/revised design. Everything fit out-of-the-box with no issues.

BUT: Power isn't smooth. 4000rpm to 7000rpm is smooth - and also terrific (very noticeably better than before) and MHD indicates 18-19psi vs 16-17psi before (the very same MHD Stage2+ tune is on). But 2000-4000rpm is a bit jerky and hesitant. The same behavior exists with all tuning stages.

My understanding is that the DME should be fine with them, but clearly it isn't. No faults are set. The power delivery is just hesitating at ~2500 and ~3500 rpm and then it unloads very nicely.

Why would that be? Clearly I've misunderstood something, but would like to know what.

(NOTE: MHD Stage 2+, 95 Octane with xHP on 6AT.)

[suspect]

My understanding is that with uprated turbos a custom tune is needed.

[AWD Addict]

That. You need a custom tune.

[oVeRdOsE.]

before a custom tune, you need a log.

I had a similar behavior on my FBO 335, and it was on stock turbos; 2000-4000; not yhat jerky, but feel like a stock N52, then over 4000rpm all the power at once, like it was insane, and fun. Feels like a huge turbo lag.
But was fine for a year or so according to previous owner. Got the car cheap for that reason.

Unfortunately OP, I did a log, never posted it, had free time, and decided to go single turbo, before looking for the issue.

While doing conversion I noted : old vacuum hose on the rear turbo, bad setting in the JB4+MHD and bad fuel sensor.

Of course I change all this, so can't really tell which was wrong, since none of them givin me a code.

Note that wasn't the turbos, sold them, and they work fine on the new car.