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We picked up our GXE yesterday and was looking over the brochure, and I'm just wondering how the Variable Valve Timing works in the 1.8 litre engine... is it a switch over like Honda's VTEC? I don't want to take my car to the limit cuz it's still in the break-in period... got like 1500km to go to get out of it, and I'm taking the car as easy as possible...
 

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i dont even know.... is that the same concept as the SR20VE?

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2000 Nissan Sentra SE - Hotshot Cold Air Intake - HP RacingMotorsport Coilovers - Razo Carbonfiber Pedals - Razo titanium shift knob - Razo Shift Light - Nology Hotwires - Arospeed Shortshifter - Smoke Side Markers
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There are several Japanese car manufacturers lingos you should be familiar with. Variable Valve Timing, and Variable Valve Lift. They sound almost the same and even try to accomplish the same thing. However, they do their job in very different ways.

Variable Valve Timing (VVT)<UL TYPE=SQUARE>
<LI>VVT - Nissan
<LI>VVTi - Toyota
<LI> I don't know what Honda calls theirs
</UL>
Variable Valve Lift<UL TYPE=SQUARE>
<LI>VVL - Nissan
<LI>VVTLi - Toyota
<LI>VTEC -Honda
</UL>
Here is how VVT works. The speed at which the camshafts rotate can be adjusted by the ECU. Changing the speed at which the camshaft rotates gives the effect of having longer or shorter valve lift duration. Shorter duration produces good low end power in addition to smooth idle and clean emissions. Slowing the camshaft down has the effect of keeping the valves open longer. This is good for higher RPM power. Having the valve open longer allows more fuel (air and gas) into the cylinder. As you can guess, having a DOHC motor means the camshafts can be timed independently (as oppesed to SOHC), another plus to having two.

Variable valve lift takes a different approach which is defenitely more effective. Fos simplicity, we will just look at one cylinder. Most modern imports have four valves per cylinder, two intakes and two exhausts. Each of these valves is opened by its own rocker arm following its own cam lobe. That would make four cam lobes per cylinder. On VVL motors, there is an additional cam lobe located between both the pair of exhaust lobes and intake lobes. These cam lobes are much more aggressive and have a lot more lift and duration than the other four lobes. They also have their own rocker arm which follows the lobe but moves independantly of the other rockers. In normal low RPM operation, the valves follow the smaller lobes. This is good for low end power and emissions and idling. At higher RPM the small lobes don't have enough lift and duration to make good horsepower. At the point where the power curve would start dipping, the ECU (usually at a preset RPM) activates a hyraulic pump which forces pins into place. These pins lock the outside rocker arms into following the the center rocker arms that follow the big lobes. With the valves now following lobes with huge amounts of lift and duration, the motor can make huge amounts of high RPM power. As you can see, this method allows a small motor to have well behaved low end performance as well as race car power when needed.

Both these methods are very effective. They give motors wider powerbands and better behavior. Without these technologies, small motors wouldn't be as good of performers as they are today. Hope my explanation was clear.

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rschauby

2001 Sentra SE w/PP auto (radium)
1998 SE-R 5spd
 
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