I am aware of tunes plus mods increasing the N54's power to about 405 bhp. Are there really tunes plus mods that can yield 500 bhp). If so, which ones because I have never heard of mods increasing that engine's power by 200 bhp? Are you talking about NOS?

 

The only way to get the N54 up to 500 hp is to replace the turbos. ASR has done it on a 1 series I believe.

 

New turbos, down pipes, FMIC ( which has to be heavily modded to fit the e60) Meth injection,full exhaust,headers, and ecu tune....it will get you close to 500, but then at the cost you could just get a 6sp M5....

Cpo 550 would be the way to go in my jaded eyes used m5 6sp or 07+DSG due to the the trans/clutch issues the earlier ones had.

 

I love my '08 535i...37K miles, and (1) fuel injector is the only issue I've had. Since I replaced the run-flats with Michelins, it is a whole new car. I hardly ever drive it any more, but did take it out this past weekend. OMG...I honestly had forgotten what a super nice car it is. It is funny...told the wife I was going down the road, just to "exercise the car"...it hadn't been driven in about 2 months....well, I stayed gone like 6 hours . I found myself at the lake...using the navigation to drive around the back roads...what a freakin' blast... This is really the first time I've ever taken the 535 out for a "pleasure" drive...I normally take the 911. Taking the 535 is a whole different experience...just as good/fun...but in a different way.

I guess all that to say to the OP...you will love the 535. Indeed, some cars have the HPFP issue....but many do not...like mine. But if it happens tomorrow, I have a warranty to cover it...for 120K miles or 10 years (I think), so I'm not too concerned about it. The 535...like ALL the 5-series...are extremely nice cars. If you have a chance to get one...do it...you will NOT regret it.