I own a 2004 645 convertible. Nice car... I love it. However, it is a convertible, so the pickup is sluggish. I took it to a tuner in NH, and he was surprised how sluggish it was, said it felt like an Audi A4. Anyways...
I want to get the engine upgraded by Hamann. The tuner increases the displacement from 4.4 to 5.2. Giving it more HP and torque (to 412hp, 550Nm). My questions are... I have many. (Feel free to answer even if you don't have a 645, but got your engine stroked... just wanna get a feel for this.)
1., has anyone done this here on this forum?
2. How much did it cost? How long did it take to upgrade your engine?
3. Where did you take your car to get it upgraded?
4. What's the minimum octane rating for fuel you can use after upgrade?
5. Also, can you get your engine supercharged (in my case) / turboed too?
6. How reliable was your engine after the upgrade?
7. Did the stroke engine upgrade also come with a high flow throttle body?
(Dinan sells these, give 8+hp, and 8+ torque for $600, hardly seems worth it, but I want to deck out my car.

What are my other options for engine upgrade other than Hamann? To me, I'd rather have more torque than more HP, since I like windy tracks, rural windy roads, and I spend more time on the streets than on the track.. so I won't be going over 120MPH much. (Incidently 120+MPH with the top down is quite scary!)
My other option is to go with Hartge. I gave them a call, and they told me I had to ship my car to Germany for the engine upgrade. I don't really want to do that. I called Hamann, and they told me that ideally, I'd have to ship my car to somewhere in California, but they were willing to work with a local tuner. (I live in New England.)
Now, I've been looking at Racing Dynamics, they have a 5.0L V8 R50 motor with 480HP, but they don't list torque. Does anyone have that number? Also, it's not clear whether they can upgrade my existing engine, or whether the R50 motor is something RD builds and I can buy separately. Anyone know?
So, if not Hamann to stroke my engine, who else? Or should I not stroke my engine at all? Questions, questions.....
thanks in advance.