VTEC disengagement conditions
 

I googled my specific question, but couldn't find the answer I'm looking for. Instead just explanations of when it engages and how it works, etc.

What I'm curious about is the conditions under which VTEC *disengages* in a stock S2000 (I've got an AP1). Obviously if RPM drops below 6K it will disengage, but I want to know if *load* is a condition as well.

e.g. RPM hits 6K, VTEC engages (presumably regardless of load, but I guess I'm not certain of that). Say we're now at 8500 RPM and VTEC is still engaged, if I let off the throttle or reduce it to 10% or something low, do the pins stay in the rockers? Or they only disengage if RPM drops below 6K?


I have a GReddy EMU + Karcepts tune and I notice a small hesitation in the car at particular throttle inputs and RPM. I didn't clue in that this is almost certainly just the VTEC engaging/disengaging at the configured 4K RPM. Obviously I know it's set up this way, and I realize it *engages* only if both the RPM and load conditions are met -- but the hesitation I experience must be the *disengagement* when I shift or the load drops below that threshold (but RPM still 4K+). It's most noticeable when I drive slightly aggressively around town -- so VTEC engages sometimes at 4K (depending on load), but I don't wind it out much past that, or I'm going around a corner and the throttle load drops. VTEC will do this engage/disengage thing that I feel as hesitation... it's my theory, anyway.

I'm kinda rambling and maybe not explaining this well, but my guess is that in stock form, either the RPMs are high enough that I wouldn't notice VTEC engage/disengage above 6K regardless of load, OR VTEC *remains engaged* until RPM drops below 6K.

Perhaps what I would prefer is the the Karcepts tune just left VTEC engaged once the load and RPM conditions are both met AND it left it engaged until RPMs dropped below 4K, which is how I *suspect* it works in stock form but at 6K instead.

For starters standard VTEC does NOT engage at 6000 rpm regardless of load. Nor to I believe it starts at any random set rpm level regardless of load.

Load (or at least throttle position) is a required condition for VTEC engagement. I don't know the details of where/how but here's my example.

Under WOT (wide open throttle) my Gernby-tuned 2006 DBW AP2 engine will engage VTEC at 3600 rpm. Easy driving stop light to stop light and shifting at 4500-ish (earlier discussions) VTEC never engages (but it lurks just under my right foot). I can run cruise control on the highway at literally any speed and VTEC is not engaged unless some load is induced (but it lurks just under my right foot). Example cruising at 80mph is 4250rpm with my gearbox -- higher than my 3600rpm nominal VTEC engagement -- and no VTEC unless or until I press the gas pedal and induce some load. You can verify this with your own tuned car. 80 in your car is about 4300rpm, above your set VTEC point. 80 or 85 of a flat highway in cruise control should provide some information. Be sure to let us know.

My ECU is the Honda OEM ECU which on the DBW cars is tunable. Your ECU may react differently.

-- Chuck

Sorry I just saw this, but to follow up, this is how the Karcepts tune is set up (info I got from Brian way back when I first was ordering mine)

"VTEC is lowered to 4,000 rpm on both our AP1 and AP2 base tunes. The VTEC transition point is load dependent, meaning when full throttle, the VTEC will trigger at 4,000 rpm every time. However, when part throttle cruising, VTEC will not engage at 4,000 rpm, and will be a dynamic rpm point much higher than that rpm. The new rpm transition point is completely dependent on the load the MAP sensor sees. For example, under extremely light load, VTEC may not engage until 6000rpm. 6000rpm is the point where you will definitely be in VTEC once you get there. We have this dynamic transition point dialed in very nicely, where you can easily cruise at 4500+ rpm on the freeway without VTEC engaging, but once you get on the gas a little more, then it will switch to VTEC (when you need it). So you definitely don't have to be worried about screaming in VTEC all the time and sucking up gas when cruising."

Worth noting, that their tune is not based on throttle position but is at least indirectly dependent on MAP. For example when i had that tune I lived at 5500FT above sea level and Vtec would not engage until close to 5000RPM at full throttle, but when I was down at sea level it would function as advertised and when I was up really high (like 9000+ feet) it would not engage until 6000 even at WOT.

Thanks for posting the note that VTEC may engage the high power cams at 6000rpm regardless -- although I'm not yet convinced. :) What we need is a VTEC indicator on the instrument panel. I'd think after 25 years these would be commonly available or have I been missing it all this time? Is the data on the CANBUS?

Cruising at 4500 is 85mph in 6th gear in our cars.

Speed in gears at 6000rpm.
AP1 AP2
1 29 28
2 44 42
3 61 58
4 78 75
5 93 92
6 112 113

-- Chuck

VTEC indicator seems to be kind of a waste of an indicator IMO. Can clearly hear when it engages. If they put an indicator in they would have a bunch of people always thinking something was wrong if their vtec yo light was not coming on when it should lol. We dont have gauges telling us when timing is advanced or retarded either because there is no real point in it.

I have never seen a Gernby tuned stock ECU. I am sure it exists but the folks I know running a Gernby tune had a piggyback and it was tuned almost exactly the same as the karcepts. On a dyno, back to back with my friends, they mostly behaved the same, mine made a few more peak HP. So I cant speak to what a stock ap2 ecu tuned by Gernby does.

Gernby FlashPro tune has been on my 2006 car since 2015. Stock AP2V2 ECU (drive by wire) is FlashPro tunable and the reason I bought a 2006+ S2000 for the ability to get a 3600rpm VTEC without an aftermarket or piggy pack ECU. No problem sensing VTEC engagement but there is no longer the massive VTEC Yo! effect as switching to the high power cam isn't as big a power jump at 3600rpm as it is to bridge the power gap at 6000. Can feel it and hear it but it isn't a kick that it would have been if we had to wait longer. Power just rolls on between 3600 - 6000, right in the rpm range we mostly drive.

Comparing dyno numbers is "Cars & Coffee talk" unless the pulls are all done on the same day on the same dyno. I neglected to get before and after dyno data on the local Mustang dyno reputed to be conservative.

You sure the guys at the high school wouldn't want a big red VTEC light in the center of the dashboard? :)

-- Chuck