Contour Enthusiasts Group Archives Forums Modifications Zetec Maintenance Same zetec as focuszx3,escort zx2, ford escape,mazda tribute.....................

DOHC means that the engine uses two camshafts per head. On an inline engine, like the Zetec, this means we have two camshafts. One on the intake side, one on the exhaust side. The main reason that a double overhead camshaft design is used is to all for more intake and exhaust valves. More valves = more openings for gases to flow = free-er flow of intake and exhaust gases = more power.

Variable camshaft timing is a way of improving performance. The opening and the closing of the intake and exhaust valves needs to be adjusted as engine speed increases. What works good at low speeds may not necessarily work good at higher speeds (referring to engine RPMs). The exhaust valve is opened a little sooner, and closed a little later. There's alot more out there on how the VTEC in Honda engines work, not so much on the Fords. Same basic principle, just that the Zetec VCT only works on the exhaust side, and only to help out emissions. This isn't anything new, the idea of adjusting when the valves open has been around since the early 1900's.

Here is an interesting link that talks about how variable valve timing and how it affects performance and emissions.

if you're gonna swap engines, shove the 3.0L taurus engine in there ;-)

VCT = Variable Cam Timing. It's a heavy hydraulic mechanism inside the timing gear that with solenoid actuation and oil pressure, can advance the exhaust cam timing as much as 20 degrees.
This is done as a replacement for the egr valve, that by changing the intake/exhaust valve timing overlap, they can suck exhaust gas back into the motor to mix with the new air and fuel coming in during the intake stroke.
This takes away room for more good air and fuel, and creates a lean burn condition. Good for emissions, bad for power.

For those who'd like to discard the exhaust vct, I have adjustable cam gears and adapters so you can take off and chuck the vct exhaust gear, and dial in the right timing for more power.

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ZXtuner Store
1999 ZX2 S/R
128.5 wheel hp @ 6250 rpm
9.62 sec @ 72.11mph (1/8)
2340 lbs.