I found this out when I was driving in Yosemite...VTEC didn't engage until nearly 7.5krpm at WOT. I got back down to the valley and it was going at 6krpm as usual. This indicates air pressure is a variable in engagement point.

Another illustration of how ambient air pressure affects power delivery: now that I have a V-AFC I set on to 5.8k, off 5.6k (the VAFC removes the variable engagement point due to ambient pressure). When VTEC engages when there's a low pressure system in the area my powerband is significantly smoother than during high pressure times without changing the MAP correction.

 

be mindful of the dreaded ignition timing map mismatch, don't linger in the DeadZone for too long

 

The shop I had it tuned at didn't lower it that much, but I dropped it further to smooth out the powerband so the car's balance isn't upset NEARLY as much as it would if I were tuning VTEC for max power. Helps a lot at track and especially autocross with the tight low-speed turns.

I did do what u said however and set my unmatch to -5% to fix the noises at steady state in the "dead zone"

 

Please don't forget VTECH makes kids toys too.

 

Josh, you are correct, the VTEC variability seems to be directly correlated to the MAP signal like you said as opposed to TPS signal. It seems, if the manifold pressure isn't within ~2 psi of ambient it starts to delay the engagement point. Kind of the same end result as monitoring TPS except with the MAP it will start dialing you back if your air filter is really dirty (wonder if they did that on purpose?). The subject of you getting suppressed at high elevations seems strange (wonder if that

 

I'd bet that the ECU has a hardcoded MAP value for VTEC engagement.

MAP changes value based on rpm, TPS and ambient pressure.

chemistry 101:
V=nRT/P
V=volume
n=mole count
R=gas constant
T=temp
P=pressure
Lower pressure also means lower density (higher volume), which means less combustion. If the ECU didn't recognize that then it could get into some serious trouble when the weather changes Based on the basic gas law, you'll have worst performance when it's hot and low pressure (HT_LP), like in a Floridian summer storm, and best performance when it's cold and high pressure (LT_HP), like the CA central valley in winter. This also means that power deltas between cam lobes change, meaning a smoother powerband in HT_LP and more noticeable VTEC in LT_HP.

c'mon Mr. freebody diagram, you should know this stuff!!

 

Yes, the sensor for that is in the driver's side (not JDM car) under the dash. I don't know the answers to your other questions.

 

[QUOTE]Originally posted by The Unabageler
[B]I'd bet that the ECU has a hardcoded MAP value for VTEC engagement.

 

Yup, and I bet you're having a hell of a time understanding the topic righ5tnow u dumbass newb..

 

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