So its my understanding VTEC will engage around 5800rpms on a stock AP1.

While the "hit" is fun, its easy to fall off the cam when not driving at 100%. I know the vtec engagement point can be changed by a VFAC or other controller. My question is what is the optimal engagement point for a stock, near stock car? I am willing to give up the hit for a more gradual but sooner increase in power. I would imagine if it was too early, you would loose some driving power because you would still be in the optimum range of the primary cam.

To those that have changed the engagement point, what rpm did you set it at and do you feel it was worth it?

 

Ideally, you'd tune it with VTEC set high, and VTEC set low on a dyno. You'll see where the power lines cross over from the two runs. And that would be your best vtec switchover point.

With a stock exhaust/cat, ~4,500 rpm-5,000 rpm. With an HFC, 4,000 RPM. With a test pipe, 3,500 rpm. Roughly. At the minimum you'd want a wideband o2 sensor to tune your air fuel ratios if you're going to be changing it yourself. Otherwise, get on a dyno and do it there.

 

So what would be the result, if I just hooked up a VFAC and set it to 5000rpms with nothing else. Will I see a power improvement from 5000-5800rpms?

 

A guy on this forum, Gernby, did some extensive testing on this. The numbers quoted for rpm for each type of cat are from his experiments. What he found is with stock cat, you'll see a big dip in power midrange if you lower vtec too much.

Its apparently why Honda didn't lower vtec for ap2. Ideally they would have, to give ap2 similar vtec powerband as ap1. But limits of stock cat preclude this option.

That said, you CAN get away with lowering it a little with stock cat, maybe even to 5.5k. But if I recall, 5k would be too far. Do some searching on this forum for Gernby's research on this, as he does state how low you can make vtec on stock cat.

 

You really should adjust the fueling as well, and not just the vtec point. The car dumps more fuel at the vtec switchover to richen it up for safety.

 

I did look into it and his research is based on the F22C. It seems the harmonics of the cat affect the optimum vtec point.

Just so I am sure, what is the factory crossover on a AP1?

 

AP1 is 6,000 RPM as well.