I'm street tuning my bolt-on ap1 on megasquirt and currently have vtec engagement set at 4800 rpms, but there is a noticeable jump in power at crossover. In searching, I found a thread referencing a ~3500rpm crossover.

What rpm are you guys switching over to the big cam? Other than highway cruising in vtec, are there any downsides to dropping it that low?

 

You do need to make more changes than just dropping VTEC but it seems 3600 rpm to 4000 rpm is the sweet spot for AP2's and on my AP1 I have VTEC kicking in (yo) at 4000 rpm based on throttle position, load etc.

 

Thanks for the response, I'm going to give 4000rpms a try and go from there. There's a table to set it by tps so I'll set light throttle high enough I won't be cruising around in vtec.

 

I have mine at 4500 and 60% throttle this what Karcepts does as well for there E Tune I just think it's the magic spot for NA with bolt ons

 

3,800rpm Gernby tune. You won't cruise on the highway in VTEC as it's dependent on oil pressure, throttle position, and something else I'm forgetting. It really wakes the car up.

 

My Gernby road tune has VTEC at 3600 rpm with a Berk 63.5mm high flow cat and the wonderful Tanabe Medalion Touring exhaust. As noted engine rpm is only one factor in VTEC engagement. Engine load, throttle position, and other factors I don't begin to understand affect this. Suffice to say cruising at 79mph on the Interstate in 6th gear at roughly 4000rpm the engine is running on the economy cam -- but VTEC is just under my right foot as the factors other than rpm kick in. 79mph? 80mph conviction here in Virginia is a felony -- keeps the lawyers fully employed. Watch your speed down here. Oh yeah, radar detector is illegal here too.

Negatives? VTEC Yo! no longer exists; no large, instant rush of power like you suddenly get at 6000 rpm with a stock tune where there's a large power difference between the cam profiles. Less of a difference at 3600 simply because the engine isn't producing as much power at that rpm -- recall that power is torque times rpm so at lower rpm you get lower power by definition. Engine just seamless and smoothly slides into more power and keeps climbing. You'll feel it but it's not a kick and is definitely faster. Exhaust note changes instantly as the power rolls on. As I've noted several times the rpms climb so fast at WOT in the lower gears I was constantly hitting the rev limiter and consequently installed a red-line beeper as the tach was climbing too fast to watch. Beep beep beep -- shift!

Wonderful back roads VTEC in 3d and 4th gears.

-- Chuck

 

I have the E-manage and it's 4000rpm for my AP1 if not a little sooner, but I agree it's the best modification after wheels+tires!

I do miss my Gernby tuned '07, it felt perfect! 3600-8500 of VTEC freedom was phenomenal. It also seems like it did richen up the fuel mixture more to help with the exhaust valve tightening as my valve clearances stayed fine for about 60k miles. The "loss" of the powerband changeover being the dramatic kick is one thing I do love/hate. It gave the car a bit more character but it's so much easier to handle knowing your powerband is more linear and you have more midrange of torque for daily driving. Ironically I seem to speed less now since I don't have to rev up as much to get up to speed.