Your stock blow off valve leaks - Kawasaki Ninja H2 Forum
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post #1 of 16 Old 04-19-2017, 07:20 AM Thread Starter
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Your stock blow off valve leaks

I also posted this on the Facebook page but I know some of the guys on don't use Facebook, so here you go.

Not sure why I haven't heard anyone mention this yet, but there is a major downside to keeping the stock compressor bypass valve. It is designed to start bleeding off boost pressure under high boost. If you are raising the boost by compressor mod or SC gears, this will be affected by your stock bypass valve. You can see a bleed hole that leads to the diaphragm that will help it start opening under heavy boost conditions. This is common on many stock forced induction engines like like the Subaru WRX. By changing to an aftermarket valve, you can eliminate this boost bleed at high pressures. I'm curious if any of the tuners have messed around with changing them to see exactly how this changes the dyno graph.

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post #2 of 16 Old 04-19-2017, 08:26 AM
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Rather than being used for a maximum boost regulator the H2 dump valve is used when you shut the throttle.

The H2 supercharger doesn't need pressure regulation like a turbo. It won't over-speed as it's mechanically driven.

The way to increase boost on the H2 is to increase the engine red-line to 14,000 rpm or to swap the supercharger gear-set to make it spin faster.

Last edited by BobC; 04-19-2017 at 08:33 AM.
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post #3 of 16 Old 04-19-2017, 08:31 AM Thread Starter
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Rather than being used for a maximum boost regulator the H2 dump valve is used when you shut the throttle.

The H2 supercharger doesn't need pressure regulation like a turbo. It won't over-speed as it's mechanically driven.
What about when you keep adding boost and don't shut the throttle?

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post #4 of 16 Old 04-19-2017, 08:37 AM
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What about when you keep adding boost and don't shut the throttle?
Boost is proportional to engine speed, from tick-over to whatever your engine's red line is.

Hold the revs steady and you won't hear the dump valve. Shut the throttle and you will hear it's characteristic twitter.
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post #5 of 16 Old 04-19-2017, 12:38 PM
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Is it possible for it to leak if load exceeds factory's settings? Well that's actually a silly question, of course it will, what I mean is, how much pressure can it hold before it leaks?
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post #6 of 16 Old 04-19-2017, 07:25 PM
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Big discussion. Succinct answer.

The hole is so air can be referenced as the solenoid applies equal pressure to both sides of the valve and then switches to vacuum under a part or closed throttle application.

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Last edited by NOLA; 04-19-2017 at 07:41 PM.
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post #7 of 16 Old 04-19-2017, 07:59 PM Thread Starter
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After having this BOV tested, it does not appear to be the same design as other automotive bypass valves that have a built in leak valve for high boost pressures. It does look the same but it functions how most aftermarket BOV would work. This one still vents to the intake, so you can decide if that is enough of a reason to replumb it or replace it. For me, I like the sound and that's it.

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post #8 of 16 Old 04-19-2017, 08:58 PM
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The function of this valve is to relieve boost pressure when you close the throttles. This valve does not function as a boost-pressure limiting device at wide open throttle or anywhere near it. Pressure is applied to the other side of the diaphragm from downstream of the throttles. If there is low pressure drop across the throttles (i.e. they're open), the same pressure is applied above and below the valve, and it stays shut.
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post #9 of 16 Old 04-20-2017, 05:39 PM
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With pressure equal on both sides the diaphram its still limiting at spring pressure ,
If you block the internal port you would have it positively closed but loose some of the backfire relieve

You guys trying the aftermarket BOV , have you compared the spring pressure to the original , my thumb pressure gauge says its a pretty good spring in there , most BOV are not anywhere near that
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post #10 of 16 Old 04-20-2017, 09:15 PM
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Ozbooster, you seem very knowledgeable about these, and many other things. Is it possible to vent the original valve to air for a more pronounced noise without causing any problems?
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