SAVAGEGEESE:
How is carbon build up managed and additional blow created from turbo associated with DI?
DAVE COLEMAN:
Carbon buildup on DI intake valves has two contributors. The oil itself getting on the valves, and the valves being at a temperature that promotes the formation of hard deposits.
We've dramatically reduced the oil in the intake stream compared to our last DI Turbo through several measures. First, oil blowing past turbo seals directly into the intake stream has been reduced with better turbo oil seals and lower oil pressure in the turbo itself. Actual blow-by has been reduced across the board with SKYACTIV engines by improving the roundness of the cylinder bores through improved analysis of casting, machining and assembly stresses that can slightly warp the bores. Taking this into account in the design process has given us much better blow-by performance.
Finally, the realization of the sensitivity to intake valve temperature has allowed us to design the cylinder head structure, cooling system and calibration to manage intake valve temperatures to prevent carbon buildup.