sleevedgsr

Honda first introduced the DOHC VTEC mechanism in the US on the 1990 Acura NSX. But a year earlier in 1989, the Japan Domestic Market got the world's first dose of DOHC VTEC in the 1989-1993 generation of the Honda Integra. The 1989 DA6 Honda Integra RSi/XSi used a 160ps variant of the B16A DOHC VTEC engine. Honda enthusiasts would recongnize the B16A engine since it is currently used in the 1999 and 2000 US-spec Civic Si and Canada-spec Civic SiR. However the B16A used in the current Civics is a second version of the original B16A. The main difference is that the newer US-spec B16A has slightly more power at 160hp.

Okay that's enough history. Lets see how DOHC VTEC works. The figure to the right shows a simplified representation of a intake-valve VTEC mechanism (the exhaust mechanisms work similarly). So for each pair of valves, there are three cam lobes. The two on the outside are low RPM lobes and the one in the middle is the high RPM lobe. The two low RPM lobes actuate the two valve rockers, which in turn pushes the valves open. The high RPM lobe actuates a follower, which is shaped like a valve rocker, but doesn't actuate any valves. The figures show the circular section of the cam lobes touching the valve rockers, and the eliptical section pointing away. Thus the valves are closed in this stage.

During low RPM operations, the two outer cam lobes directly actuates the two valve rockers. These low RPM lobes are optimized for smooth operation and low fuel consumption. The high RPM lobe actuates the follower. But since the follower isn't connected to anything, it doesn't cause anything to happen. This procss is illustrated by the figure to the right.

At high RPMs, oil pressure pushes a metal pin through the valve rockers and the follower, effectively binding the three pieces into one. And since the high RPM lobe pushes out further than the low RPM lobes, the two valve rockers now follow the the profile of the high RPM lobe. The high RPM lobe's profile is designed to open the valves open wider, and for a longer duration of time, thus allowing more fuel/air mixture to enter the cylinder. The improved breathing allows the engine to sustain its torque output as RPM rises, thus resulting in higher power output.

Yet as you can see, the implementation is elegantly simple. VTEC is Honda's solution to the design goal of improving engine breathing at high RPMs while retaining smooth and economical operation at low RPMs. DOHC VTEC technology is currently used in the 160HP Civic Si, 170HP Integra GS-R, 195HP Integra Type-R, 200HP Prelude base/Type-SH, 240HP S2000 and the venerable 290HP Acura NSX. And these are just the US-spec cars.

SiR Inspired ED7

iTrader: (1)

read this before, i guess i know my Dohc Vtec if thats how u consider it

PatrickGSR94

iTrader: (1)

I thought the 1st gen B16 was first used in the Civic before the Integra?

NightRiderS2K

Where are the little pictures (aka: figures?)...

Pictures make everything look nicer.

illi Adik

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by PatrickGSR94 &raquo;</TD></TR><TR><TD CLASS="quote">I thought the 1st gen B16 was first used in the Civic before the Integra?</TD></TR></TABLE>

So did I...??

You_Get_Vapors

Once you go DOHC VTEC you neva go back.

DFW

iTrader: (1)

Calsonic

I've ridden in cars that have Variable Valve Timing, etc.. like Toyota's VVTi, Ford's Zetec, Mitsubishi's MIVEC, Nissan's VVL & CVTC, etc. But NONE of them have the distinct crossover sound like DOHC VTEC. Can anyone explain why you can hear the crossover on Honda's but not on any other car manufacturer?

95 integra

iTrader: (2)

maybe because you hear the secondaries opening and not vtec? Dont forget some other manufactures "vtec" is what honda calls VTC and not true vtec anyway.

DOHCGsr

i also think it is the secondaries. i am not a toyota or a ford guy but have hammerd the pedal to the floor on both an none of them compare in my mind. I think the DOHC VTEC is the only one with secondaries which makes it sound much more distinct.

Calsonic

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 95 integra &raquo;</TD></TR><TR><TD CLASS="quote">maybe because you hear the secondaries opening and not vtec? Dont forget some other manufactures "vtec" is what honda calls VTC and not true vtec anyway. </TD></TR></TABLE>
I can clearly hear VTEC crossover at 4400 RPM and then at 5800 RPM I also hear the secondaries open up. VTEC crossover is much louder than the secondaries on my teg.

Calsonic

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DOHCGsr &raquo;</TD></TR><TR><TD CLASS="quote">i also think it is the secondaries. i am not a toyota or a ford guy but have hammerd the pedal to the floor on both an none of them compare in my mind. I think the DOHC VTEC is the only one with secondaries which makes it sound much more distinct.</TD></TR></TABLE>
The B16A & B18C5 don't have secondaries, so your theory wouldn't work.