vtec disengage point?
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From: Wylie, TX
Originally Posted by Wisconsin S2k,Mar 21 2005, 03:47 AM
I do know that in stock form, the vtec disengagement point is LOWER than the engagement point.
I'm not claiming that it isn't lower (since it makes sense for it to be a bit lower), I'm just wondering what the actual value is. In all honesty, I could see Honda setting the crossover to a set value (for engagement and disengagement) just to simplify their own life. I know, however, that the VAFC gives you the ability to set the disengagement point lower than the engagement point, so maybe the stock ECU does the same thing.
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From: You wish
Honda puts a deliberate hysteresis into its VTEC activation/deactivation protocol. While I don't know what the disengagement point is for the S2000, it is lower than the activation point. This is to prevent rapid switching back and forth if you were to be holding steady throttle in a corner, etc.
Not only is there a hysteresis based upon rpm, but it is also load dependent. At high loads (low vacuum) VTEC activates lower, at low loads (higher vacuum to a point), VTEC activates at a higher rpm. You can confirm this by noting how much later VTEC activates at very high altitudes (say 5000+ ft). We notice this driving from sea level up the Angeles Crest highway.
UL
Not only is there a hysteresis based upon rpm, but it is also load dependent. At high loads (low vacuum) VTEC activates lower, at low loads (higher vacuum to a point), VTEC activates at a higher rpm. You can confirm this by noting how much later VTEC activates at very high altitudes (say 5000+ ft). We notice this driving from sea level up the Angeles Crest highway.
UL
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From: Dry Branch
UL is correct. VTEC engagement is based on several factors, including vacuum and RPM. Gentle acceleration causes VTEC engagement at a higher RPM because vacuum is higher (or as UL might put it, the load is lower).
What I'm unsure about is whether or not the disengagement point also varies with load. If we accelerate gently to 6500 RPM, VTEC will not engage, but if we then floor it, it does engage. If we back off at 7000 RPM, does it then disengage because the load dropped, or are we locked into VTEC until the RPM's drop below some fixed disengagement point? Guess I'll have to play around a little next time I take the car out to see what happens. (This isn't the kind of thing I'd be doing in normal driving.)
Anyone already tried this?
What I'm unsure about is whether or not the disengagement point also varies with load. If we accelerate gently to 6500 RPM, VTEC will not engage, but if we then floor it, it does engage. If we back off at 7000 RPM, does it then disengage because the load dropped, or are we locked into VTEC until the RPM's drop below some fixed disengagement point? Guess I'll have to play around a little next time I take the car out to see what happens. (This isn't the kind of thing I'd be doing in normal driving.)
Anyone already tried this?
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