What is VTEC?

VTEC – Variable Valve Timing and Electronic Lift Control.

Now, what in the world does this mean?!?! lol.. On Honda motors (and most other motors utilizing a reciprocating assembly – crank, pistons, and the like) the valves control the air that enters and exits the motor. The camshaft, or cam, rotates and pushes the valves down to open them; and lets them up to close them. The crankshaft spinning spins the cam by the use of a belt or chain. DOHC and SOHC are used to describe the number of cams a motor has. DOHC means Dual Over Head Cam and SOHC means Single Over Head Cam. On a DOHC motor (such as the B16A2 found in the 99-00 Civic Si) there is 1 cam for the intake valves and 1 cam for the exhaust valves ; this is much better for making power. On an SOHC motor (such as the D16Y8 found in the 96-00 Civic EX) there is 1 cam for both the intake and exhaust valves. Now, something called a rocker arm connects the cam lobe (the part that pushes the valve down, looks like an oval...) to the valve. Now, there is usually 2 rocker arms working before VTEC is activated. Now, when VTEC engages (the ECU, engine control unit, activates VTEC) some oil pressure activates a third rocker arm. This makes the large VTEC lobe push the valves down instead of the smaller lobe that is in use before VTEC engagement. This allows more air in and out of the motor - therefore making more power.
The B16A2 found in the USDM 99-00 Civic Si engages VTEC at 5500rpm. It makes 160hp out of a 1.6L!!!! That's a 100/1 power per liter ratio! But, it only makes 111lb./ft of torque. The 160hp is made at a high 7800rpm. The reason it makes all that power is because of VTEC.

The point of variable valve timing is to create overlap at high rpms, or periods of time at which both the intake and exhaust valves are open simultaneously. What this does is create a bit of a suction, as the pressure of the exhaust gases as they are exiting the cylinder leaves a low pressure area in the cylinder, that the open intake valve allows air to fill, and mix with gasoline. This extra air/fuel mixture naturally equals more power. So the purpose of variable valve timing is to draw in more air at higher rpms and create more power. The follow-up question to this is why not use this variable valve timing at all rpms for more power? The answer here is that these characteristics work wonders for creating power at high rpms in naturally-aspirated motors, but they actually discourage power production at lower rpms. The overlap does not work well at engine speeds where the motor easily obtains the air it needs to make power. Variable valve timing is effective at drawing in air at those engine speeds where usually only forced induction will supply the air needed to make more power. Beyond that, Honda's VTEC system uses cams that have three lobes for each pair of valves. The two outer lobes open and close the valves when VTEC is not engaged. Once the VTEC criteria are met (VTEC is controlled by five factors (which are escaping me right now), including rpm, coolant temperature, throttle application, and a couple others), a set of VTEC rocker arms lock in place, joining the retainers of both valves, so that both valves operate off the single, larger cam lobe in the middle. This cam lobe opens and closes the valves allowing for the overlap as described above.

 

Hey I already posted all of that!! Boo-Hoo....

 

really?? sorry something told me to use the search this ..Damn it!! sorry!

 

I don't care man...more knowledge the better!

 

alrighty

 

an extra squirell:slap:

 

maybe this will helps
http://auto.howstuffworks.com/question229.htm
or
http://asia.vtec.net/spfeature/vtecimpl/vtec1.html
or
http://www.leecao.com/honda/vtec/dohcvtec.html
or
http://www.youtube.com/watch?v=AcT_ZyY3F0k <---Video

 

The YouTube Video

The You Tube Video is a Good One and Spoon Did a Good Video I Just have to Find It Again...

 

hope this hepls

 

it's spelled wrong, you're missing an H...it's supposed to be spelled V-TECH. lol, just playin'.:roflmao:

 

lol... V tach!