Project Evo IX Part 7: Cosworth Rocks!
By Mike Kojima
When we last left off on Project EVO IX, we had increased the capacity of the fuel system with larger injectors and improved the flow of the intake and exhaust tract with a bigger throttle body and less restrictive intake piping. We also did some ECU tuning to produce a significant jump in power.
|We selected Cosworth M2 MIVEC cams for Project Evo IX.|
For our next round of tweaks, we obtained a set of Cosworth M2 cams for the MIVEC variable cam timing version of the 4G63 found in our EVO IX. Camshaft design is very tricky with many of the aftermarket offerings not being engineered to control spring surge induced valve float. Consideration of higher order harmonics is unheard of and valve spring tension is simply increased to enable higher revs and more aggressive profiles. Cosworth being an engineering intensive company considers this stuff and uses this as consideration in their profile design. Most of the aftermarket cannot compete with Cosworth engineering's prowess and their extensive validation testing in design optimization.
|To ensure valvetrain stability to 8000 rpm, we used Cosworth single high rev springs. The springs feature a conical shape to give them more coil bind height in less space. We WPC treated our springs for better fatigue life and cooler running.|
Fighting spring surge is always an issue with high performance engines. The spring's natural frequency must be matched to the acceleration of the cam's ramp angles to avoid exciting the valvetrain which can cause surge. If the system is engineered correctly surge can be controlled passively by design and a lower tension spring can control valve float. Lower spring tension means less friction, more power and less wear. Having an engineered spring/cam system means that it's not a good idea to mix and match components between manufacturers.
|Our stock camshafts had heavy wear despite their being a roller design and our engine having relatively low miles. Because of this wear we decided to WPC treat our Cosworth cams before installing them.|