The 08 M8 Turbo has far exceeded my expectations with respect to performance, however part throttle runnability issues have proven a challenge. This due primarily to my lack of understanding of the fuel control functions, specifically the roll the exv value plays. The exv fuel is added to combat a lean condition which exists just before the valves open, that being said the 08 has a dual stage valve operation, with a mid open value of 130, full open value of 90, and closed is 157. The original mapping called for a BD exv value of 85, this is an un obtainable value, as even at full open that value would not be achieved, therefore the added fuel (around 5 pts) would begin at your min rpm parameter (likely 5500) and not stop until your max rpm parameter (likely 7500, this induces a lean step during primary ramp up for aux injectors and will result in an almost certain ecu 21 code. Not to mention the bizarre midrange anomalies that accompany unwanted fuel. I found through rigorous testing the best exv value to be 140, this ensures fueling stops as valves are activated. Remember if you have been tuning with the 85 you will now be short on fuel below 7500 (if that was your high) and after valves open, so add to low boost numbers but not too much as the duty cycle assignments of the boost map are 2 to 1 greater than the rpm nodes. (each boost pt = 1% DC, each RPM pt =1/2% DC) so be careful. As for the for the sheer performance nothing compares, not even the run of the mill apex turbos. With regard to the 120 hour install discussed earlier it takes me 11 hours start to finish and I am not superman. It will likely take a garager longer or anyone doing there first kit, and it is a job best left to a professional. Every connection, clamp, splice, tube, hose, fitting, etc. must be installed with utmost consideration for leak prevention, period, if there is so much as a question in your mind about a hose routing or barb seal, etc. re do it until you are absolutely positive it will not leak or chafe, ever. Every tuner who does an install should snow tune the unit with his or her costumer to tailor the mapping to better suit the end user, this generally takes 3 to 4 hours. The waste gate setting is critical and after install and prior to riding a proper calibration must be done. I use a mighty vac hand pump fitted with a pressure guage to obtain proper adjustment. The reason for this that the turbo timing is often altered during install, and is most often not very close when new.
Another point of contention is the CPC vs the BD turbo kit, though this is wholly against the focus of this thread, it seems appropriate to discuss. The BD is hands down, no question, absolutely, much much faster, even with both kits set at 10psi the BD runs away. The BD is much harder to learn to tune, much harder to learn to ride and is much more complicated both to install and to understand. The CPC is a nice, comprehensive, easy to install kit that is both easy to tune and easy to ride, it costs too much, and its not fast enough, and if you turbo trouble get out your tow strap and your wallet. Considering the kind of monetary outlay that a turbo kit represents, I feel when all is said and done the thing better be ridiculously fast, not kind of fast. Enough said.
