PAIR System

[XXTi]

I was wondering about the PAIR system today. Is it anything more than a breather system? Does it serve any other purpose?

I know it pipes vapor from the valve cover into the air cleaner via a solenoid valve, but I don't understand how it would change the air/fuel ratio readings in the exhaust as some have said.

Any thoughts?

[Redbird]

I know it pipes vapor from the valve cover into the air cleaner via a solenoid valve

That's backwards. It channels fresh air from the airbox into the exhaust stream under certain conditions.

[tomek]

It does not " pipes vapors from valve cover into the air cleaner" etc.It supplies exhaust ports with fresh air on decel to clean up the emissions.Basically secondary combustion takes place in exhaust system.

Readings for CO and CO2 will change when PAIR operates,and since simplified but not accurate Dynojet system converts those numbers into A/F ratio you get what you get .Actuall A/F ratio will not change.

[XXTi]

Thanks guys. That helps to explain it. I had it backwards.

How does the air get from the valve cover into the exhaust ports? Does it only operate on Decel?

I'm getting a PC-II and a dyno run in a few days and I am wondering how the PAIR system will change the A/F readings on the Dyno-Jet.

[XX4me]

If I'm not mistaken the hose attached to the valve cover operates like a PCV valve to remove vapors from the crankcase, the other end is connected to the air box.

The PAIR system adds air to the exhaust by way of the vacuum created in the port as the exhaust flows out the header.

[XX4me]

There is a MOD talked about in some circles that is supposed to

gain a few HP.

It involves removing the PAIR system and then connecting the two hose fittings on top of the cylinder head with a T that then goes to the valve cover fitting.

They call this the PAIR sucker MOD.

Basically the theory behind it is it's using the PAIR reed valves in the cylinder head to create a vacuum in the crankcase supposedly creating better seating of the rings thereby increasing HP as much as 3-5 at topend.

I say supposedly because I've never seen any DYNO sheets proving it, though I have heard it's done alot for drag racing as a simple HP increase.

[XXTi]

If I'm not mistaken the hose attached to the valve cover operates like a PCV valve to remove vapors from the crankcase, the other end is connected to the air box.

The PAIR system adds air to the exhaust by way of the vacuum created in the port as the exhaust flows out the header.

That's what I was thinking in my original post. I'm still not quite clear on how the vacuum connects to the header. Wouldn't the exhaust have to be directly connected to the crankcase/valve cover to do this?

[Redbird]

There three hoses going from the valve cover to the airbox. One is a normal vent line. The other two go from a set of two reed valves on the valve cover hrough a solonoid operated (on the FI version, it may be vacuum actuated on the carbies) valve that the ECU decides when to open.

The normal vent line is unrelated to the PAIR system.

I can't tell you how the air gets from the reed valve to the exhaust stream, which is odd because I just had it all apart a bit ago. I wasn't looking for it, though. I pulled all the PAIR shit off my bike last year.

There's some pictures with the valve cover off here if anyone thinks that'sll help clear this up. I don't understand how it works past the reed valves, personally.

[EVLXX]

I'm getting a PC-II and a dyno run in a few days and I am wondering how the PAIR system will change the A/F readings on the Dyno-Jet.

It will make them basicly useless.

It will give you false readings.... almost all the way through the RPM range.

My .02, either Remove the Pair system before the pull.... or don't bother with the AFR's.

[Northman]

I can't tell you how the air gets from the reed valve to the exhaust stream, which is odd because I just had it all apart a bit ago. I wasn't looking for it, though. I pulled all the PAIR shit off my bike last year.

There are ports from the underside of the valve that channel the air into the exhaust port.

[Northman]

You can see them here in this pic, one beside each spark plug hole on the exhaust side.

[XXTi]

Thanks again for the info. I got off my ass and looked in the service manual. There's a nice description of the system near the front of the book.

I couldn't understand how Honda kept the oil from just running into the exhaust, but now I do. Those holes are sealed up by the valve cover gasket and o-rings.

Any recommendations on what to do with the PAIR system during the dyno runs?

Edited to say that I see the ports BESIDE the spark plug holes now. Not inside as I said before.

[Redbird]

Talk to Red J and see if he has any of these bad boys left-

Now, I'm not sure it's going to make a difference in your typical full throttle dyno run. My impression (and it's just that) is the the PAIR system only operates under certain off throttle conditions. It may very well mess with A/F readings in the exhaust in certain on/off throttle situations, so finer tuning may be affected, but most runs are of the "spin it up to 10,800 at full throttle" variety. Pretty sure the PAIR system isn't an factor at WFO.

[Red J]

Pretty sure the PAIR system isn't an factor at WFO.

I thought so, too, but I seem to recall a few forum members (EVLXX? trurotor2?) saying that the WOT numbers were more stable with the PAIR defeated.

I can't confirm, sadly.

---

The system allows air to vent from the airbox into the exhaust port. A vacuum operated solenoid valve (or electric solenoid valve on FI bikes) controls when the air is "injected" which I understand to be upon deceleration, in order to assist the unburned fuel. Reed valves in the valve cover keep the exhaust from backflowing into the main valve.

I suppose it is possible for air to be drawn in past the reeds every cycle, from the passing of an exhaust pulse where there may be some negative pressure. But I can't verify that's what's happening.

At least that's the way I understand it.

J.

[EVLXX]

My before and after AFR numbers did change... on and off the throttle.

Before I removed the PAIR unit,I was getting readings of 13.1 at full Pull.

Then after I removed the unit... 12.2, so it definatly affects the readings even on a Full Pull.

If I understand the exhaust cycle correctly, each down tube would have it's own low pressure wave after every firering of the cylinder. So each downtube would suck in some amount of air after every Exhaust cycle it that tube. And would therefor dilute the Exhausts AFR, even under full acceleration.

[EVLXX]

I can't confirm, sadly.

J.

Ha...You just Did... sort of in a backwards way...

Yes... the AFR's were more stable or steady, after the removal.

[Redbird]

If I understand the exhaust cycle correctly, each down tube would have it's own low pressure wave after every firering of the cylinder. So each downtube would suck in some amount of air after every Exhaust cycle it that tube. And would therefor dilute the Exhausts AFR, even under full acceleration.

Mmmmm, can't argue the numbers, but I was under the impression any vacuum in the exhaust would open the reed valves, as I believe you're saying, but if the solonoid operated valve outside the valve cover (controlled by the ECU) was closed, there'd be no air to be had.

No chance of an air leak on any of the PAIR plumbing on your bike, Eric?

Edit- Dammit, J editing your post like that. Sounds like we're on roughly the same page, anyway. So, if the solonoid operated valve is closed, where would the air come from?

[EVLXX]

If I understand the exhaust cycle correctly, each down tube would have it's own low pressure wave after every firering of the cylinder. So each downtube would suck in some amount of air after every Exhaust cycle it that tube. And would therefor dilute the Exhausts AFR, even under full acceleration.

Mmmmm, can't argue the numbers, but I was under the impression any vacuum in the exhaust would open the reed valves, as I believe you're saying, but if the solonoid operated valve outside the valve cover (controlled by the ECU) was closed, there'd be no air to be had.

No chance of an air leak on any of the PAIR plumbing on your bike, Eric?

Well when I removed it... everything looked to be in perfect order.

But, more to the point I guess, I thought that the PAIR system would only close, by the ECU, on decel.... that way it wouldn't get the dreaded exhaust Pop.

I don't know when it was really open or closed, but that seamed to make sence to me.

... ?

[Redbird]

Ahhh, so you're saying the solonoid valve doesn't open on decel (which was my impression, don't know why), but closes?

You numbers make more sense if that's the case. Time to go look at the manual I suppose........

[Red J]

I believe it opens upon part throttle cruise as well as decel in order to assist the burning of unburned fuel, cleaning up emissions.

AFR normally goes way lean upon decel in cars, but that doesn't mean that HC or CO goes down...

[EVLXX]

I believe it opens upon part throttle cruise as well as decel in order to assist the burning of unburned fuel, cleaning up emissions.

AFR normally goes way lean upon decel in cars, but that doesn't mean that HC or CO goes down...

I don't think it's open on Decell... That would let cool fresh air in with the super heated lean exhaust gases and create a lean backfire. Usually on decell the full mixture is too lean too fire in the cylinder... so it passes through unburnt, and if it were to meet up with a bunch of cool fresh air.... POP!

Or that's what I understand anyway.

[EVLXX]

Ahhh, so you're saying the solonoid valve doesn't open on decel (which was my impression, don't know why), but closes?

You numbers make more sense if that's the case. Time to go look at the manual I suppose........

Yes, and yes.... or...

Maybe it's time too hook a small light up to that dangling plug in...

see when it turns on...

and then bench test the seloniod to find out which way is open or closed. :wink:

Just another thought.

[Red J]

Or that's what I understand anyway.

It appears that I am in error

With the engine running, gradually apply vacuum to the PAIR control valve.

Check that the air intake port stops drawing air, and that the vacuum does not bleed.

If the air drawn in [sic], or if the specified vacuum is not maintained, install a new PAIR control valve. If afterburn occurs on deceleration, even when the secondary air supply system is normal, check the air cut-off valve.

The valve in the diagram is sprung open, and the vacuum shuts it. High vacuum (such as occurs upon deceleration) should close the valve.

Guess that explains why the readings go bonkers under wide open throttle. Every time a power pulse goes by, the negative pressure wave will pull some air thru, with nothing to stop it.

[XXTi]

I think the manual says that the valve opens and allows air flow with 12 volts applied on FI bikes, but that may be backwards. Can someone please translate the following?

"Check that the air should not flow (a) to (, only when the 12V battery is connected to the PAIR solenoid valve terminals."

(a) comes from the airbox and ( goes to the reed valves. (see page 5-83 in the shop manual)

Why couldn't I just disconnect the plug for the dyno runs? It sure sounds quick and easy, so there must be something wrong with the idea.

Eric, I'll sure be interested to hear what you find with your solenoid bench test.

[tomek]

I don't think it's open on Decell... That would let cool fresh air in with the super heated lean exhaust gases and create a lean backfire. Usually on decell the full mixture is too lean too fire in the cylinder... so it passes through unburnt, and if it were to meet up with a bunch of cool fresh air.... POP!

PAIR opens on decel in order to burn that unburned fuel.This way the emissions are better,HC I think.EPA does not care about backfire. I recently reconected my PAIR system and sure enough I got some burbling and poping from the pipe.It did not do that without Pair.

As far as marring PAIR with crankcase venting,if lines and ports are big enough it should work.There are aftermarked systems that create negative pressure in crankcase using scavenging in exhaust system,basically big reed valve connecting headers with crankcase.Lower the pressure in crankcas the better,bigger hp.

There is couple factors,lower aerodynamic drag of spinning crankshaft and conrads,less oil from oilpan being picked and ending up on outside crank surface creating power loss and better sealing of piston rings( rings seal by pressure difference above and below them.(BTW that is why you see those deep sumps on never supersport bikes,or dry sumps in pure race engines where room is not a problem).If you care about max hp on wet sump engine ,oil level should be as low as you can get away without starving oil pump.

The way the crankcase is vented on ramaired XX is just plain stupid as far as power is concerned.In high speed run there is positive pressure in airbox and airbox is connected with crankcase via hose ,so there is additional pressure there due to ramair effect.But it is illegal to vent crankcase into atmosphere ,so Honda did what they did.

BTW there is another trick.You can reconnect air pump( XX does not have one ) so instead of pumping air into exhaust system it sucks blowby from crankcase.

There is a lot of tricks like this that tuners use to build race engins.2 hp here ,3 hp there ,0w20 oil,loose bearings here are there, etc,single mod does not seems to be much,but if you add up all of that end result is nice,powefull engine.