How does VTEC work? - Honda-Tech - Honda Forum Discussion

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How does VTEC work?

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Old 07-20-2015, 03:16 PM
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Default How does VTEC work?

I'm going to post a statement describing how I THINK VTEC works. Will somebody please confirm or correct?

The B16A G1 I4 engine is a 16-valve DOHC engine. There are 2 intake valves and 2 exhaust valves per cylinder. One cam operates the intake valves, the other cam operates the exhaust valves. Looking only at the intake camshaft, there are 3 lobes for each cylinder, the lobes referred to as Primary, Mid, and Secondary. Looking only at one cylinder-grouping of lobes on the intake camshaft, all three lobes have the same open/close/duration timing measured at 1mm, but they each have a different lift. The Primary lobe operates one intake valve, while the Secondary lobe operates the second intake valve. Primary and Secondary lifts are slightly varied to improve intake swirl. With some techno-magic I won't concern myself with, the VTEC lobe engages at 5500RPM with a decidedly larger lift to operate BOTH intake valves to enhance engine output at higher speeds.

The exhaust cam operates on the same principle.

Is that about right or am I off somewhere?
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Old 07-20-2015, 03:58 PM
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Default Re: How does VTEC work?

Duration and lift differ on all three lobes, and it is an oil pressure driven mechanical system that locks the Primary and Secondary lobes to the VTEC/Mid lobe when the computer directs such action by electronic solenoid.

Otherwise, you just about got it.
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Old 07-20-2015, 05:15 PM
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Default Re: How does VTEC work?

Thank you. I finally thought to look for an animation to see it in action. I think I understand it better now; still not something I want to use in my project as I want to go retro with as few electronics as possible.

Pretending the middle/VTEC lobe isn't there, are you telling me that primary and secondary do not have the same duration?

Also, (VTEC lobe back in play), do the three lobes at least share the same centerline?
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Old 07-20-2015, 08:42 PM
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Default Re: How does VTEC work?

Some have similar duration for the primary and secondary lobes and some do not. Differing lift/duration typically increases swirl and thus, increases volumetric efficiency.
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Old 07-21-2015, 05:13 AM
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Default Re: How does VTEC work?

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Old 08-22-2015, 05:47 PM
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Default Re: How does VTEC work?

During your research let me know if you find out more about 3rd gear VTech
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Old 08-23-2015, 11:37 AM
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Default Re: How does VTEC work?

Voted power!!!
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