Exhaust Valve Closing
Exhaust valve closing is dependent on intake port flow, exhaust port flow, and intake valve opening. Poor flowing exhaust ports with a lot of backpressure need to have the exhaust valve closed earlier in relation to the intake valve open to reduce overlap. The high exhaust backpressure can pollute the intake charge if the overlap is too great. Basically an engine with poor flowing exhaust ports won't benefit from much overlap. If the exhaust port flows well and the intake flows well then it can be beneficial to close the valve later and allow for more overlap. Another scenario is a good flowing exhaust port and poor flowing intake port. This combination can benefit from more overlap because the evacuating low-pressure exhaust gas can help draw in the intake charge and increase intake port velocity. This is not the case in our turbocharged application where most likely our intake side flows better than our exhaust side.

As testing is drawing to a conclusion, I've started to see a pattern in the cam profiles that I can correlate to dyno data along with what I've learned from my research. I can see things like lift profile and opening/closing events making a significant impact on performance. Although some cams are advertised as having the same duration, the rest of the picture (profile) and the dyno data shows a huge difference. I still have at least one camshaft to test, the TOMEI 280 solid lifter cam, that I'll compare to its hydraulic counterpart. In addition, the next and last installment will include a comprehensive camshaft summary along with some of the conclusions I've drawn about the cam designs and how they performed.

Oliver Rods
Grand Rapids
13401 S. Main St.
Los Angeles
CA  90061
AMS Performance Ross Pistons
625 S. Douglas
El Segundo
CA  90245
GSC Power-Division Tomei Powered USA
13 Orchard Road, suite 107
Lake Forest
CA  92630
"The engine specialist"
Supertech Tial sport
Forced Performance AEM
BC Brian Crower Crane Cams
530 Fentress Blvd.
Daytona Beach
FL  32114
Kelford Cams