I've had an 03 SL55 for nearly a decade now and for the last few years have really thought hard about stepping up to an SL65. Given that there weren't a whole lot ever made, it is rare that I've seen one for sale anywhere within 100 miles of me. Well just this week a dealer about an hour away got an 05 in so I made the trek over to give it a test drive. First impressions were good. The nappa leather interior is leaps and bounds ahead of the MBtex on the SL55 (at least in my opinion as I don't care for the course grain on MB tex or even in real leather). The exhaust at idle also sounded great. Dealer said that the service department relayed that the car had been well cared for, but just the short test drive and closer inspection made me feel otherwise. The center console wood was cracked and you could feel some vibration in the car from the drive line, likely from engine mount failure. In the SL65 the engine has to be removed to replace the mounts, which is approximately a 20-25 hour job. The car had 62k on it so likely the expensive carbon ceramic front rotors were still good, but probably didn't have a whole lot of life left. They mentioned some exhaust work had been done, so it is possible that it was not done well and that is what the issue was, but it sure felt like failed mounts to me. Given how much people rave about the smoothness of the v12 I was pretty let down, but again that could have just been because of a bad exhaust job or bad mounts. Whatever they did to the exhaust (not sure if muffler delete, resonator delete, cat delete, or some combo as I didn't take the time to look under the car) I disliked. Again, it sounded great at idle, but once you were going it, to me at least, sounded like an old tractor rather than a top of the model line motor. It might just be my bias loving american muscle cars, but the SL55 v8 sounds much, much, better to my ears. The other thing I noticed is the absolutely awful turbo lag at low RPMs. The car felt like it was really straining below 3k RPMs and having to rev way too much to get out of its own way, almost like a car with a stall converter does. Once 3k was hit, though, and the turbos really going it was clear that the 65 is definitely faster than the 55. The slower 5 speed transmission really shows it's age in the 65 b/c of the slow shifting getting exposed by the turbo lag. In the supercharged 55 it is pretty much instantaneous power at any time and any throttle position and driving around in a non maniac fashion feels a lot faster than the 65 even though I know in a straight line over a longer distance it's not even close. Perhaps in the later R231 v12 models that got the faster shifting 7 speed (though still torque converter equipped instead of MCT like the 63 turbo cars) things don't feel as laggy, but the test drive really solidified my decision to keep the 55 and throw speed parts at it (I already have an 82 TB & 550 injectors, but will be added MBH headers, extra heat exchanger, and 80mm pulley). The speed parts should bring me up to or higher than a stock SL65 in terms of top end power and it be instantaneous instead of lagging and exposing of the slow stock transmission (I'm also going to upgrade from a eurocharged TCU tune to a MC Ultra one). The only positive that I really liked from the 65 was the interior and if I could find a wrecked 65 or 600 (they had the same interior) and swap my 55 over to it I think that would be the most ideal combo. At some point if I can find a 17+ (facelift year of the R231) 63 to test I might step up to that, but finding one without MBtex I'm sure will be more impossible than finding a 55 without MBtex. I know the 5.5 M157 doesn't have lag and is great from my time driving a 2014 CLS63 that has all the renntech upgrades to it (exhaust, turbos, etc.)

I also test drove a brand new GLC63 too while I was there and the quickness of that transmission and amazing sound of the engine further cemented in my mind just how ancient the driveline tech of the 65 feels and how much a love the sound of a V8 over a modified exhaust V12. I have never heard a factory stock exhaust sound as good as the motor in the 63 C/GLC cars. It is simply amazing. I've test driven an E63s and it seemed very muted in comparison to the C/GLC. As soon as my dealer gets an allotment available to order a GLC63 I'll likely go that route as the ones they had on the floor had a bunch of options I didn't want or care for and were missing ones I wanted. Right now they weren't willing to negotiate anything off price, so if I'm gonna pay sticker for something I'd rather it be exactly what I want and likely be much less than the ones they had on the floor.

 

Eh, I'd use your gut. Exhaust sound seems to be important to you and it sounds like they've messed with it a bit. That can surely create vibration that makes it FEEL like something's off, but regardless, those mounts don't last forever -even with the low mileage.

If you're just WANTING to own a 65, go for it. There aren't too many left. But if you're wanting to "upgrade" your 55, I'd at least keep them both, as I'm afraid you'd be disappointed. The leather is certainly nice, and you can get a tune to account for some of the poor low end performance. I wouldn't say though that the 55 is "not close" to the 65. I had an '06 S65, and stock, it would want NO PART of the 55s I've had with just minor modifications.

Just my $.02

 

Sounds to me like you answered your own questions. I will say that the SL65 should be butter smooth, so yep, sounds like the one you drove had a collapsed mount. The V-12 delivers gobs of power down low, so I can't believe turbo lag is an issue. On mine the power is huge right off the bat and then when the wastegates close it's just endless pulling. I wish I had space for an SL55 as well, but be assured that a well kept SL65 is an absolutely rewarding and grin inducing experience.

 

Problem with the SL65 is, you very very rarely find one which is driving like it does from the factory. Over the years nearly all suffer from poor maintenance, not properly bled intercooler, electric gremlins, bad spark-plugs, not full boost, worn out engine mounts etc.etc.

The car needs some love (and money) from the owner, which is rarely spend because everyone think they are "cheap now".

I would try one which is running correctly or with a good ECU-Tune. No turbo lag, massive power starting from idle. In my opinion in another league like the Sl55 in a straight line, escpecially at higher speeds the SL65 is much, much faster and smooth as silk. A great car!

Best

 

Something is seriously wrong with the SL65 if it is not impressive off the line. They do not suffer from turbo lag at all. The V12 is a masterpiece in sound, smoothness, and low end power. I loved the bi-turbo V12's I've owned. It's the rest of the car that is not good.

As much as I like the bi-turbo V12 and R230 styling, I would go with an R231 and bi-turbo V8 due to reliability of the 231's ABC system and support for modifications on the M157.

 

While I haven't driven an SL55, the SL65 had good power down low, but you could definitely feel the difference once the turbos spooled up and the boost kicked in, you suddenly had to grip the wheel a lot harder and stiffen up your arms as your neck went back into the headrest. It definitely has some "lag", but I wouldn't necessarily call it lag, more like power, and then HOLY MOLY HOLD ON MORE POWER