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A little bit of a background: My power valve butterfly solenoid does not activate, and it stays closed at all times. I will be remedying this issue soon. I recently confirmed this situation when I mounted a light and camera in the engine bay while driving. When I put my foot into it, the engine did some talking and rocking, and it was interesting to see what takes place (or doesn't) under the hood while in motion. I've read on the web that some people were curious of whether the power valves, or butterflies as they're called, made any difference. I wanted to subjectively identify this for myself, too. Today, I drove my 2004 SE-R a distance of 140 kilometers (87 miles) with the valves full open all the time. When returned home and shut the car off, I flicked the valves closed. Here is a bit of what I found during that duration.

On start-up, the engine blubbered and idled a bit louder. The exhaust sounded throbbing, and initial driving under 60kmph (37mph) at 20 degrees Celsius (68 Fahrenheit) resulted in fuel consumption metered at over 14L/100km (16.8 mpg). I would normally see start-up consumption around 11L/100km. Once the engine was at temperature and road speeds of 80kmph (50mph) were the norm, consumption dropped to about the usual 6.9-7.5L/100km (31-33mpg) for the duration. Some areas around 2000RPM were louder than normal, but the stock intake and helmholtz resonators are effective at silencing the would-be intake growl.

Having the valves open resulted in a loss of low rpm responsiveness and lack of power. It felt pretty weak, and while it didn't catch my attention right away, it did when I finally tried to accelerate with tire spin at 50% throttle. Wasn't happening. Instead of the jerk it gives with I stab the throttle with closed power valves, I just got a soft feedback and mild increase in RPM's. As I bared down on the pedal from 50% to 100% open throttle, I didn't really get any notable increase in power in these lower RPM's, only loss. As the RPM's increased, the power notably increased (towards it's almost-normal self) around 3000-4000RPM, but with a Vtec-like upward swoop of the engine tone. If I had to choose between open and closed, I would drive with them closed. Once I have the solenoid functioning again, I will not need to make a choice.

 

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Yup, its better to keep them closed. How often do you drive at 5200+rpm anyways when they are only ever really useful. And cool investigation work
 

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I thought it has been dyno proven the butterflys produce gains when open and above 4500rpm
Minimal. The difference isn't even worth it.
 

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Someone needs to do this on a boosted setup. I'm keeping my butterflies even at my goal of 20psi. They'll just be open under positive manifold pressure.
 

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I thought it has been dyno proven the butterflys produce gains when open and above 4500rpm
http://www.b15sentra.net/forums/showthread.php?t=166796

Looks like there are some gains in the upper rpm, but with a bigger total loss (judging from the area under the curve) down low. Torque loss is also significant, although not shown.

I think 5250 makes more sense, since it's where HP curve finally supersedes the torque curve.
 

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A window switch was used, splash did it and graced us with his how-to. I picked up a window switch with plans to do so but upgraded to the 2nd gen mani so now it sits around in a box and collects dust.
 

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You can actually feel the difference with the valves open all the time vs operating normally. I'd prefer them operating normally. I'll revist that later with the 2007+ plenum that's sitting in my garage.
 
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