I don't know if this is the correct section for these questions, but I figured it was a good place to start.

My 5.5 6MT exhibits a power drop/dip between 3500 and 4000 rpm as shown by the dyno below. The engine is completely stock, was dyno'd in 3rd gear (may be wrong, don't have the raw data) and the car had aftermarket wheels & 6th gen brakes.

I originally believed this power loss was due to a MAF issue which caused hesitation upon throttle applications greater than 50% at this engine speed (originally posetd: http://forums.maxima.org/7342248-post48.html). Although I no longer believe this is the case as the new MAF has corrected the hesitation, but not the power dip (as felt by my butt dyno, recently calibrated).

Therefore, my questions are:
-Is this normal (other stock/baselines seem to corroborate, noted below)?
-What causes this, and how can it be corrected (VIAS activation at 3600rpm, bad knock sensor)?

What say the all motor gurus?



http://www.nissanclub.com/forums/eng...-vs-stock.html


http://forums.maxima.org/dyno-discus...-6mt-dyno.html


http://forums.maxima.org/dyno-discus...6mt-stock.html


If you ignore the performance post 5000 rpm:
http://forums.maxima.org/dyno-discus...irst-dyno.html

 

VIAS activation.

 

Damn, can this dip be improved while retaining the VIAS system?

 

This happen on my 6th gen WITH the BOP there was a drip

With the VIAS mod my curves were climbing smoother without a dip.

are you having any ignition issues ?

 

+1

 

To clarify, with the stock VIAS the was no dip, but without the VIAS (using a block off plate) there was a dip?

To he best of my knowledge I do not have an ignition issue. The aforementioned hesitation has not reoccurred after the 2k1 MAF installation.

 

Moved.



And yes that dip is a result of the VIAS activation (power valve open) @ precisely 3600 RPM.

 

Yea the same thing happenend with my dyno.. imy afr also leaned out to 17 or 18

 

Aside from removing the VIAS system, is there any way to improve the system?

I seem to recall from a prior thread, which I cannot locate, the VIAS generally closes (unintentionally) at higher engine speeds which also hurts outpput. Is this correct?

 

I don't see that being VIAS related at all. I would first take the knock sensor out of the equation, I wouldn't be suprised if it's tripping right there and pulling timing out the ***.

Silly question but what Octane was that dyno done with?

 

Finally, a thought that allows me to spend some money.

The runs were made with 93 octane E10 and an ambient temperature of ~55 degrees Fahrenheit.

How would you recommend testing the knock sensor, or dyno'ing without one? Perhaps remove the sensor from the engine and use a jumper to ground it.

 

At all?





OP: Simple test. Remove and plug the vacuum line going into the power valve actuator and take it for a spin and see if you feel the same dip in power.

 

I guess the opposite argument can be tested (VIAS versus other causes). This may need wait a few days until it's either not snowing or stupid cold.