Gernby

It isn't just a matter of lowering hte VTEC engagement point to get more power. Each car has some "optimum" RPM where VTEC should be engaged, and it changes based on mods, climate, and altitude. Honda set the stock VTEC engagement at a level high enough that it would always provide a kick. If VTEC is set below the optimum RPM, there will be a loss in power. If VTEC is set above the optimum, there will be a kick. If VTEC is set right at the optimum RPM, there will be a smooth, seamless transition in power providing the maximum "area under the curve".

If you do lower VTEC engagement (with a V-AFC or eManage), you should do it on a dyno with a wideband O2 sensor. You will need to adjust the air / fuel ratios to safely engage VTEC before the ECU expects it.

Dezoris

No one talks about gearing, and how well the car is geared to make use of the engines power band.

Most people worried about making power are not concerned about lower RPM operation. Even if you pick up a 10HP increase with tuning who cares, because if you are upshifting at a high RPM your RPMs will never fall that low in the power band.

It's not a Civic or Integra, where you redline a shift and your upshift drops you out of power for 500-1000 RPMs.

I don't understand the point

Gernby

Dezoris,

Lowering the VTEC engagement is not going to make a significant difference for drag racing, but that isn't the point. If VTEC is set to engage at the optimum RPM for your setup, and it is well tuned, the car is much more enjoyable to drive. It also helps quite a bit for road racing and autocrossing where shift points are not so cut and dry.

Gearing has nothing to do with this topic.

bilkanin

I would suspect that Honda could have set the vtec engagement earlier, but considering gearing setup and highway driving it might not be beneficial for a factory car.

However, there should be some gains to be made in the mid-range when lowering vtec in addition with some mapping, and it would be nice to have vtec engaged further down to avoid - however short it is - the transition time when going into vtec.

I haven't seen any numbers on it, but I've heard about some guy changing his vtec to 4500rpm and he was happy about it.
Fuel consumtion might rise drasticly though.

terd ferguson

I'd set VTEC just above highway cruising speed rpm's. You don't want to be on the race cam just cruising on the interstate. There is tons of power to be made with lowering VTEC engagement. Stay tuned for my dyno results after VAFC. Its been done, just not posted about.

mxt_77

gernby & MattG are right on. With the stock ECU, you aren't going to be able to just lower the VTEC x-over point and gain much power. Like MattG said, the stock ECU will still be on the "low cam" fuel & timing maps, and these maps will not provide optimum power on the high cam. Using a VAFC to lower the VTEC x-over point as well as alter the fuel map will help make some power, but the timing maps still won't be optimized. To make maximum power, you'd need a fully customizable ECU so you can modify the timing & fuel maps to maximize power throughout the curve. There is a thread on here somewhere that shows a guy that successfully lowered his VTEC x-over to ~4500 RPMs and made more power than stock. He was using a AEM EMS for his tuning, though. Here's that thread:
https://www.s2ki.com/forums/index.php?showtopic=228852

Liemoanh

This thread has taught me alot.

The reason I posted this thread was because my dyno sheet shown a lose of 15 rwhp from 5,000-6,000 rpms. This resulted from running the stock Comptech ESM which made my car Very rich. I just thought that lowering the Vtec point would result in takeing away this problem spot in the dyno sheet.

I guess I was just trying to take the cheap way out.

Thanks for all the good information.