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post #1 of 13 (permalink) Old 07-25-2018, 08:35 AM Thread Starter
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Sucker Mod / PAIR Reed valve / Negative crankcase pressure

I have done a search and read the last thread I found from 2016.

I had an interesting discussion tonight with a gentleman that had a superstock spec race bike. We discussed negative crank case pressure, specifically, rerouting the PAIR to gain/suck air from the 'PCV' instead of removing them...

Now I understand this is one of the great internet debates however, I would like some insight if anyone has done some real world testing or knows something that they can add.

Another thing that comes to mind is, when does the pair valve actually suck air? Even if there are gains from potential vacuum created, there would need to be a constant vacuum to ensure pressure isn't built up which could instead cause damage.
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post #2 of 13 (permalink) Old 07-25-2018, 09:01 AM
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Re: Sucker Mod / PAIR Reed valve / Negative crankcase pressure

And what happens when it isn't.... Do people really think the ventrui suction through the exhaust ports has more vacuum than the filtered side of the airbox? You're right in that it's a debate. But not one worth having until someone puts a pressure gauge on it.
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post #3 of 13 (permalink) Old 07-25-2018, 09:32 AM Thread Starter
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In the case of a turbo car it'd be hard to argue. However, on a modern day sports bike I don't think that's the case as they rely on positive (more pressure) in the air box to make some of their power (ram air). The aim of a lot of the designs is to create positive pressure (more pressure) within the air box. Venting into the airbox could be less than ideal.
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post #4 of 13 (permalink) Old 07-25-2018, 11:51 AM
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Re: Sucker Mod / PAIR Reed valve / Negative crankcase pressure

There's been debate on that too. Does ram air actually create positive pressure, or just lessen the negative?
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post #5 of 13 (permalink) Old 07-25-2018, 06:15 PM Thread Starter
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I agree, most likely just makes it less negative. This is something that generally doesn't happen on then exhaust side of the head.

Also there would be a way to negate any positive pressure from the exhaust side of the head(when its not scavaging). One could use one way valves and still have a connection to the air box, just have the pair 't' into it.

The reason why I ask is I have removed my PAIR, Reeds and all and am about to do the same for a friend's bike. I am questioning whether that's the best route, or I should leave it in and reroute the plumbing.
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post #6 of 13 (permalink) Old 07-26-2018, 06:59 AM
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Re: Sucker Mod / PAIR Reed valve / Negative crankcase pressure

Don't have to worry about any positive pressure if you leave the reeds in.

The question is why? What are you trying to gain? You have to block it off when dyno tuning, but during normal operation all it's doing is injecting fresh air into the exhaust to burn off unburnt fuel. Racers remove it to try and shed weight, but on a non race bike there's absolutely nothing to gain (unless you have an o2 sensor and auto-tune). The best way to do it is just remove the hoses and put caps on all the hose barbs.


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post #7 of 13 (permalink) Old 07-26-2018, 11:06 AM
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Re: Sucker Mod / PAIR Reed valve / Negative crankcase pressure

+1 to the above.
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post #8 of 13 (permalink) Old 07-26-2018, 07:52 PM Thread Starter
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Re: Sucker Mod / PAIR Reed valve / Negative crankcase pressure

The bike is being setup to race, although maybe I am no quick enough to notice the difference, I do enjoy tinkering with the bike.

I have in the past just pulled the PAIR out, and purchased smart moto block off pates that come with the right resistors so if I don't go with Woolich (or the like) it wont throw a fault code.

This recent conversation has got me thinking if it really could be done to achieve some (albeit minor) power gains.

Is it worth rerouting, with a series of one way valves and a t piece into the PCV or just block them off and remove all associate hoses with the PAIR, enjoy the minor weight savings and call it day?
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post #9 of 13 (permalink) Old 07-27-2018, 08:05 AM
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Re: Sucker Mod / PAIR Reed valve / Negative crankcase pressure

Keep it simple.
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post #10 of 13 (permalink) Old 07-29-2018, 07:44 PM
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Re: Sucker Mod / PAIR Reed valve / Negative crankcase pressure

I have blockoffs installed and don't want to uninstall them to do this. But if you want to tinker, I suggest that you install one or both pair valves, connect the inlet(s) to a vacuum gauge, and go for a ride. That would provide some numbers to base a conversation on instead of endless speculation.
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post #11 of 13 (permalink) Old 12-11-2018, 04:52 AM Thread Starter
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post #12 of 13 (permalink) Old 12-11-2018, 12:41 PM
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Re: Sucker Mod / PAIR Reed valve / Negative crankcase pressure

I wish you'd used a simple dial vacuum gauge instead of a manometer and had gone for a ride. Still, that's useful information. Thanks.
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post #13 of 13 (permalink) Old 12-11-2018, 04:03 PM Thread Starter
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Re: Sucker Mod / PAIR Reed valve / Negative crankcase pressure

Quote:
Originally Posted by BillV View Post
I wish you'd used a simple dial vacuum gauge instead of a manometer and had gone for a ride. Still, that's useful information. Thanks.
Yea no doubt, unfortunately I couldn't get my hands on a proper vacuum/boost gauge, that would also be easier to mount so I could go for a ride.

It's rigged so it can easily be tested again in the future which I may also do a few 1/4 mile runs with the vacuum gauge on.

In any case I've set it up so it can never get worse than the factory crankcase ventilation. You're welcome, glad it's useful.
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