Even though Calibras dont use any VVT technolagy I thought it would make an interesting red.
A quick guide to VVT Variable Valve Timing Lift.
Even though Calibra’s don’t have VVT I though it would be an interesting topic to discuss. The most common type of Variable Valve Timing is cam phasing which alters the angle (advance or retard) of the inlet and/or exhaust camshafts altering the valve lead/lag and overlap. These systems don’t alter valve lift or duration as they are only altering the point at which the cam shaft acts on the valves and so are inferior in terms of high end performance to Honda VTEC and Toyota VVTL-I. Cam phasing offers a more varied and smoother operation as they can adjust the cam phasing in increments were as Honda VTEC and Toyota VVTL-I have an abrupt change of cam profile.
The following are all types of cam phasing:
Audi (VVT)
BMW (VANOS)
Toyota (VVT-I)
Nissan (NVCS)
Nissan (N-VCT)
Mazda (S-VT)
Porsche (VarioCam)
Suzuki (VVT)
Subaru (AVCS)
Hyundai/Kia (CVTT)
GM (DCVCP)
Ford Variable Cam Timing
Honda VTEC-E:
This system is designed to lower emissions and fuel consumption as it opens only one inlet valve at low engine speed to introduce a swirl in the combustion chamber causing the air/fuel mixture to mix properly keeping the fuel in suspension allowing a leaner and more efficient burn at low RPM so making it a lean burn engine. At high rpm the second inlet valve opens allowing more air/fuel mixture into the combustion chamber increasing its volumetric efficiency thus more performance.
Honda DOHC VTEC:
This system is used in the high performance Honda engines such as the NSX, S2000, Type-R and Vti engines. It is designed to enable an engine to produce high engine specific outputs by the use of a harsh cam profile while maintaining drivability and low down torque. It does this by having two cam profiles and operates on both inlet and exhaust valves. This allows the engine to approach higher engine speeds with out sacrificing low end torque. This in turn allows shorter gears meaning more torque produced by the engine actually is put down on to the tarmac. It uses six cam lobes and six rockers per cylinder rather than four on a conventional 16v engine. There are four normal lobes operating 4 valves in the usual way, then at 5700-6000rpm a hydraulic actuator engages two pins which locks the rockers together and this allows the extra lobes on each cylinder with high lift and duration to operate the valves.
Honda VTEC SOHC:
This system is similar to the DOHC VTEC except it uses one camshaft to operate both inlet and exhaust valves. The engine still has 16 valves but only the inlet valves are operated with by VTEC with the extra cam lobe.
Honda I-VTEC DOHC:
This is DOHC VTEC with added cam phasing.
Toyota VVTL-I:
Toyota also use a similar method to alter cam profile and it is very similar to Honda’s VTEC but it uses one cam lobe for low profile and another for high profile and it switches from the low profile cam to the high profile cam at around 6000rpm.
Nissan VVL:
This system works allot like Honda’s VTECand has six lobes per cylinder.
Mitsubishi (MIVEC)
This system works allot like Honda’s VTECand has six lobes per cylinder.
Rover VVC:
Another rather odd system is the Rover VVC which uses eccentric cams which can rotate off centre. This means that the cam timing can not only be advanced or retarded but also the duration altered. There is also a small amount of increased valve lift. This system only operates on inlet valves and uses two half cams on the inlet one being driven by another cam belt from the exhaust cam. This system also operates in increments. The disadvantages of this system are that it can only ever operate the inlet camshaft and only achieve minimal amounts of varied lift.
