why are dohc better?

Originally posted by 2ndGenTeg
Well, SOHC engines will never be as good in an all motor setup, because of the overlap issue. They simply are not capable of ingesting as much air/fuel as a DOHC is.

However...

In an FI setup, overlap is a bad thing. When the air/fuel is under pressure and both sides are open, you get blow by, which is exactly what it sounds like- the air/fuel passes right through the combustion chamber and out the exhaust, with out ever being ignited. Now you know why most turbo cams have a shorter duration than all motor cams- it's much easier to tune that way.

So if you're planning on doing a "moderate" FI setup, a SOHC engine can be just as good as a DOHC. However, you still lose the flexibility in specs and timing.

Just to elaborate, in case someone isn't following. As long as you don't need overlap, SOHC can be just as good. But if you want to change the intake vs. exhaust timing....you'd need a new cam for SOHC, whereas with DOHC you can change them relative to one another.

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