^^ are you saying you don't drop below 6k rpm or you don't feel that you drop out of vtec power-wise?

 

Ijust brough up my dyno and got a straight edge out! power headed north at 5750rpm!

 

i can almost swear that mine changes depending on various conditions...

 

I didn't expect so many responses. Thanks guys.

Let's take stock for a minute, and seperate what we know for sure from the things we are just guessing about.

I know the following to be factual:

1) With an F20C VTEC engagement takes place at 6,000 RPM, and disengagement takes place at a little below that. The disengagement point has to be lower than the engagement point to prevent constant engagement/disengagement at a steady engine speed that matches the engagement point, and it also insures that the AP1 doesn't drop out of VTEC on the 1-2 shift.

2) The procedure for testing VTEC engagement in the shop manual does not requre the use of a dyno or driving the car, so the test is run under a no-load condition. To test VTEC engagement, you bring the engine up to normal operating temperature (three bars), then rev the engine to over 6k and look for the signal that engages the VTEC selenoid. If it appears and VTEC doesn't engage then you are directed to check the oil pressure, and if it doesn't engage you are directed to check the wiring. To me this certainly seems to say that if you have temperature, oil pressure, and over 6k, the selenoid gets a signal, and I know for a fact that if the selenoid is engaged and there is oil pressure, VTEC has to engage (unless one or more of the pins are stuck).

3) Some people are experiencing VTEC engagement at other engine speeds. Either VTEC is actually engaging without them realizing it, or their car is operating in a way that would cause it to fail the VTEC engagement test spelled out in the factory shop manual. I don't think early engagement would result in the car failing the standard test procedure, but failure to engage at 6k would point anyone following the factory test procedure to the steps for trouble shooting an engagement problem.

Somebody PLEASE check the shop manual and let us know if I'm getting any part of this wrong. LOL, I am an old fart, so my memory may not be what it once was.

 

^^Red, does this mean that it could vary depending on the amount of oil you have in your engine? like if it's a little low on the dipstick?

 

I don't really know the F22C, but this seems to make sense, because it drops below 6k on the 1-2 shift, and an earlir engagement point would keep the car in VTEC after the shift. It would be nice if somebody would also look at an AP2 shop manual and see if there are other factors involved in the engagement logic. I really can't comment, becaue I just don't know enough about the newer engine.

 

No. I can't recall the exact number, but it takes something like 50-80 lbs. of oil pressure to overcome the springs and engage the pins, so as long as the oil pickup down in the pan is getting oil there will be plenty of pressure. Now if the oil level drops low enough it is possible for all the oil to be pushed to the back of the pan during hard acceleration, and if it all moves away from the pickup, the pickup only gets air and the oil pressure drops, causing VTEC to disengage. That's why some people have reported VTEC engagement problems that have been traced to a low oil level. VTEC is basically a switch which is either on, or off.

 

this is a good site with some good diagrams

http://world.honda.com/automobile-technology/VTEC/

also, according to wikipedia:
Switching between the two cam lobes is controlled by the ECU which takes account of engine oil pressure, engine temperature, vehicle speed, engine speed and throttle position. Using these inputs, the ECU is programmed to switch from the low lift to the high lift cam lobes when the conditions mean that engine output will be improved. At the switch point a solenoid is actuated which allows oil pressure from a spool valve to operate a locking pin which binds the high RPM cam follower to the low rpm ones. From this point on, the poppet valve opens and closes according to the high-lift profile, which opens the valve further and for a longer time. The switch-over point is variable, between a minimum and maximum point, and is determined by engine load; the switch back from high to low rpm cams is set to occur at a lower engine speed than the up-switch, to avoid surging if the engine is asked to operate continuously at or around the switch-over point. The DOHC VTEC system has high and low lift cam lobe profiles on both the intake and exhaust valve camshafts.

 

http://www.hondahookup.com/info/vtec.php

this article also supports that vtec engagement/disengagement is dependent on several variables/inputs.

btw, by my saying that throttle position is a variable, i'm not implying that you need to be in WOT.

 

You can clearly see VTEC engagement in the torque curves. Both engines engage VTEC at exactly the same engine speed. Because the jump in torque starts just below 6,000 RPM, the VTEC pins are engaging just before 6,000 RPM. There is simply no other explination for the rise in torque starting below 6k. Notice also that the 6000 PRM line on the grid cuts right through the middle of the jump in torque, which is why it feels like the transition is taking place AT 6k rather than before or after.

Just for grins, count the number of grid blocks under VTEC power and torque curves for both engines. This is the area under the curve, and something some people like to debate (even though it is what it is and isn't really debatable ).

The F20C spans three blocks across the graph, while the F22C spans two. The average height of the F20C torque curve over the three block span is somewhere around 130, while the F22C across the two block span averages over 140. Let's be generous and call it 145. Now the area is the width times the average height, so the F20C has an area under the VTEC torque curve of 130 times 3, or 390. The F22C has an area under the VTEC torque curve of 145 times 2, or 190. The situation is similar with the power curves, with the width increasing the area far more than the height of the curve. HOWEVER, cars with the F22C are not any slower, becaue they have more area under the curve below VTEC, and about the same area under the entire curve. If you don't believe me, count the grid blocks, estimate the average power and torque over each range, and multiply it out for yourself. Since you can so easliy SEE the area under the curves in these two plots we shouldn't have to put up with any more arguments about their relative magnitudes.

It's funny, becaue I kept thinking that the shop manual said to rev to 6k to test VTEC engagement, but I actually though engagement took place AT 6k, becuae that's the way it feels, but looking at the dyno plots it's obvious that engagement actually takes place before we feel the extra torque (which, in hindsight, makes perfectly good sense).

One more thing guys. I know for a fact that when I come down a freeway on-ramp at a steady 6k in second gear, and then nail the throttle as I straighten out, the car is already in VTEC and ready to leap forward instantly. I'd suggest trying it, but if you're not careful the sudden leap forward might get you into trouble.

One more plot. Here's one showing the nice VTEC bump you get with a Comptech SC/AC.



Check out the area under that VTEC torque and power curve. Average torque over the range is about 180, and 180 times 3 is 540 (compared to 390 stock). Hving a torque curve that slops upward rather than downward is a real hoot.



Those of you posting links to articles, while I appreciate the effort, I've read the articles already, and they are in conflict with the factory shop manual. Since I know the test procedure in the shop manual actually works, I'm inclined to believe that it is the better choice if we want factual information. Maybe the ECU does monitor throttle position and disengage VTEC when the throttle closes, but that wouldn't really make sense, becaue it would mean that VTEC would engage and disengage every time you stabbed and released the throttle. That would just be wasted motion, so I can't imagine why Honda would do it that way.

Anyway, what say we use the shop manual as our source of reliable information, rather than something someone outside Honda has written about the car?

Am I the only one here who thinks the factory shop manual is the best and most reliable source for this kind of information?