Lately I've noticed a lot of people around here saying that the F23's have some type of variable vtec cross over and thats why there is a misconception about the V-AFC's not working on the F23's, though they do because I've had one on for almost a year.

Can someone explain whats the deal with this "varibale vtec" on the F23's in 6th gens, is it pre- i-vtec?

 

the V in VTEC stands for Variable. that is probably not the most appropriate word to use.
VTEC= variable-valve timing electronic-lift control

 

I know what vtec is,
though some people here have said that the F23's have a different method of vtec cross over as variable, instead of a costant rpm where the switch in cam phase happens.

Does anyone else on this forum remember hear about this in posts about V-AFC's not working on F23's?

 

If you use a V-AFC, it will just make it fixed at a certain rpm point. It would be a better use of money to get a S-AFC. You won't give up the variable x-over, and you can still change the fuel parameters.

 

This thread was so wrong that it pained me and I was compelled to post.

As some of you may know I work on ECU's ... a lot.

*Most* Hondas have varying VTEC crossover RPM points relating to throttle postion & engine load/duty cycle... HOWEVER in extensive gimpy-testing I have found that even with that said the cars always enguage VTEC at/near the same time.. its really hard to say.

The best example I have of this is the Civic (since those are the ECU's I mainly work on)

Offset Hex RPM
6542h CA 4626.48
6543h CD 4814.04
6544h D5 5314.2
6545h D8 5501.76
6546h CA 4626.48
6547h CD 4814.04
6548h D5 5314.2
6549h D8 5501.76

As you can see the Civic (p28) has many potential crossover points, but in all my testing (I have a test bench) it ALWAYS crosses over @ 4800RPM.

So whats this mean? It means the variable factor in VTEC crossover is really a moot point and you should tune on a dyno whats BEST for YOUR application. When im tuning a rom for someone I always set every VTEC x-over to the same RPM... and thats all she wrote.

If you wish to learn more about Honda ECU functionality you know where to find me!


[Modified by GimpyAccord, 11:17 AM 2/27/2003]

 

what is the point of vtec?

 

GimpyAccord: I'm just trying find out if there is a special case in the F23's for the vtec cross over. There have been people posting out there that the F23's have some different form of vtec engagment, due to the post put out by apexi on their web site about V-AFC's not working on F22's or F23's.

My question is simply is there any difference in the F22's and F23's vtec engagment compaired to other honda vtec motors. There's a lot of people out there saying that there is and I was wondering if there's actually anyone here that can explain this without too much bitching.

I know that the vtec engagment is dependent upon other factors such as throtle position and others, though the point of crossover should be at the same rpm. Back to my idea about this is that there is no difference in the F23's and other honda vtec motors becuase I have a V-AFC on mine that works fine.

 

I see no reason why, mechanically speaking, a VAFC wouldnt work. I mean its the same head basically as a F22B1 with a standard Honda 12V solenoid to turn on/off VTEC. I used a MSD RPM activated switch on a friends 1995 Accord when his ECU's VTEC output died for 2 weeks until we could find a new P0A ECU. The only thing I see as an issue would be the ECU, maybe Apex thought they might not be able to get around it.

One thing to remember is if your fuel/timing maps arent optimized for that earlier VTEC x-over then the chance of you LOSING power is high.

I've never really paid much attention to the F23 ECU's, they have ZERO interest to me since they're A. OBDII and B. OBDII

Could the ECU vary the x-over point? Sure. But as I said in EXTENSIVE dyno pulls with a Civic and an Integra that VTEC x-over never changed, no matter how much load or how little/much throttle it was being fed... it always popped at 4800.

So in closing yah, I agree with you .. no reason a VAFC shouldnt work IMO.


[Modified by GimpyAccord, 1:09 PM 2/27/2003]