- Thu Dec 20, 2007 6:30 am
#34786
JDMB16LSD95COUPE wrote:i could have been told wrong but i was told that the sohc vtec cam is on the exhaust side thats why they are good for boost?
As someone already corrected, SOHC VTEC acts on the intake valves, not the exhaust. But you can still talk about how VTEC affects the exhaust valve timing in relation to the intake valve timing (the exhaust timing is stationary while the intake valves open sooner, open higher, and for longer).
VTEC is not wholly good or bad for boost. It's not ideal. N/A applications benefit from lots of overlap so the exhaust can suck incoming air into the combustion chamber. Boost shoves air in, so you want to close the exhaust earlier to trap it in there (less overlap).
VTEC increases the overlap, duration, and lift. More duration and lift are great for either N/A or FI. Overlap is good for N/A, not good for FI.
Now back to SOHC vs DOHC, most of the power increase comes from adjusting the intake valves. It's hard to fit all the VTEC lobes onto one cam, so Honda only did the intake side. But the increased overlap is still there. There really is no advantage for FI to either type of VTEC. The DOHC will benefit more simply because those engines are more powerful and stronger internally than SOHC.