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Old 11 Apr 2010, 01:16 pm
Join Date: Aug 2007
Posts: 35
Default What tells Vtec to Engages Vtec?

What tells vtec to engage, i know how it works and shit but what tells that cam to lock?
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Old 11 Apr 2010, 01:31 pm
Jin Jin is offline
Join Date: Jun 2008
Posts: 68

The ecu

Electronic Control Unit
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Old 11 Apr 2010, 01:46 pm
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Join Date: Aug 2007
Posts: 481

In earlier versions of VTEC, the engine's computer (ECU, PCM, whatever you want to call it), reads a signal from a sensor or multiple sensors, either tach sending unit or oil pressure (or both) to determine at what time to engage the second set of rocker arms and the higher lift camshaft lobes. Once it hits the right levels, it will lock the rockers and thus engage the additional, larger camshaft lobe. If memory serves me, it's actually oil pressure that locks the rockers together, but I could be mistaken on that.

Edit: I am actually not mistaken according to the website I found.

Here's the description of how it mechanically works:"Picture, if you will, one cylinder of a DOHC, 4-valve per cylinder engine. There are 4 cam lobes, each directly operating a valve (two intake, two exhaust). The VTEC system has two more cam lobes, in between each pair of the other respective sets. These two can then be our high-rpm lobes, while the other four are the low-rpm lobes.

The low-rpm lobes in this case then actuate the valves through a set of rocker arms, so that the mechanical connection can be broken if desired. The third, high-rpm lobe also has it's own follower, but it is in a freewheeling state, flopping around and not contributing anything. As our engine accelerates through it's rev range, it passes through the power peak of the low-rpm lobes. Then, at the engine speed and throttle position programmed into the computer's memory map a signal is sent which electronically opens a spool valve, which then directs oil pressure to a mechanical sliding pin. This pin locks the rocker arms actuating the valves to the follower on the high-rpm cam lobe. As this grind is steeper and higher then the other four cams it will supersede them. In a few milliseconds you have completely altered the valve timing and the engine's power band begins anew. "

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Old 11 Apr 2010, 02:01 pm
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Join Date: Apr 2010
Posts: 2

there's a little leprechaun that lives under the came cover, when you hear the duuuh sound that's him talking to the cam.... da diddily de.. potato's
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