I recently picked up a 2009 MCS with 87000 miles on the clock. It seemed pretty peppy, but in order to see how well it was performing I took it to the drag strip and it did a disappointing best time of 15.7 @ 87mph in the quarter mile. I decided it was coked up valves and after doing Seafoam and CRC valve cleaning, with little improvement, I decided to do the DIY Harbor Freight blasting. It went pretty well thanks to a lot of online tutorials. My valves were pretty bad, but I was surprised that in some cylinders one valve would be much worse than the other. Also, my valve stems were nowhere near as bad as some I've seen. Maybe the Seafoam and CRC did their job there, who knows. Anyway, back to the strip, best time 14.8 @97 mph. Pretty much in line with the magazine road tests. BTW the car is bone stock. So I hope this was helpful to those who might be curious as to how much performance loss you are getting from carboned up valves.

 

Have an oil catch can on the car?

Which cylinder had more crud in it?

 

I put a catch can on it as a preventive measure soon after I purchased the car. Cylinders 3 and 4 were probably the worst. 1 was almost as bad, 2 was the least carboned.