Poll: Does the PAIR System... ?

[DrDyno]

Hi All,

When I blocked off the PAIR vent in my airbox, I saw my idle drop about 300 RPM.

Because the PAIR System (Air Injection into the exhaust gases) takes air from the Air Box, I believe blocking it off leads to a Leaner A/F Mixture... it seems to me that if the PAIR System is blocked and isn't sucking air out of the airbox it will add to the airflow being sucked into the throttle bodies.

I would appreciate any input from the Collective on this issue.

[bartonmd]

This is an interesting question... Especially at idle, it won't change the amount of air into the airbox, because the stock filter is able to flow plenty of air for the engine...

On the other side, though, with the exhaust not sucking PAIR air into itself any more, I suppose it could change the exhaust scavenging by having hotter air, and less of it...

Mike

[XXTi]

I don't think it actually changes the A/F ratio at all. I think it does make the A/F ratio appear leaner at the exhaust by injecting air into the exhaust stream. The engine doesn't know the diference.

[bartonmd]

I don't think it actually changes the A/F ratio at all. I think it does make the A/F ratio appear leaner at the exhaust by injecting air into the exhaust stream. The engine doesn't know the diference.

With a MAF system, I would agree, but with either a carb, or a MAP system (like the 'bird has), if you change the VE of an engine, the engine doesn't know and has to compensate for it. This is why PC's and jet kits exist. I just don't know is the difference in airflow going into the exhaust would make enough difference to notice anything.

Mike

[EVLXX]

When I blocked off the PAIR vent in my airbox, I saw my idle drop about 300 RPM.

The real question would be.... how does it affect the AFR reading accross the RPM range ?

I think the only true way to test this would be to put some exhaust gas temperature sensors, and go from there.

But it's probably not worth the effort.

[tomek]

Let`s not forget that PAIR is not on all the time,,,,,,,,,,,,,there is selenoid valve there,,,,,,,,,,,,,

It is on on decel.,but when motor is idling,,,,,,,,,,,,I don`t know,,,,,,,,,,,anybody wants to hook up voltometer to that valve and,,,,,,,,,,,report later ?

I don`t see PAIR changing idle speed by 300 rpm,,,,,,,,,,,,,airbox is huge ( and free flowing) compared to PAIR holes ( they are abour 4-5 mm dim.),there can `t noticabale pressure drop when PAIR is sucking air out of airbox.

[cbrxxquad]

Where is Red when you need him???

Ok, this is what I think is going on in the pair system. There has to be enough of exhaust flowing by the port in the head that leads to the reeds to pull a vaccumn. This is the only way air can get into the exhaust as the pressure is high. When the exhaust opens the pressure is high as 200 psi in the cylinder and the exhaust is not flowing yet and the piston is half way down the cylinder. By the time it gets to the bottom the gas in the pipe is at the same pressure as the cylinder and is flowing as fast as it can, but then the piston starts up and the pressure goes back up. Only when the piston gets to the top does the pressure ever go negitave. This is overlap and the column of air in the exhaust having mass pulles on the droping piston after top dead center when the intake and exhaust are both open. 'This is when the reeds see neg pressure and if the solonoid is open will draw air from the box.

However, I think the valve is only open when the throttle is closed, so to burn the unburned gasses still in the cylinder and crankcase and throttle bodies when you back off the gas.

I have a graph of before and after pair valve removal afr, but it is on my other drive that goes in my 2500 compaq that is being replaced with new as it has been overheating. Should be back next week and if I can remember this thread, and how, I will show that there is not much difference, after.

[EVLXX]

When initially building my PC2 map.... with the PAIR unit still intack...I couldn't tell when the seleniod valve was closed.

I also think that the flow of the gas itself, probably causes a draw even before TDC of the piston.

[cbrxxquad]

When initially building my PC2 map.... with the PAIR unit still intack...I couldn't tell when the seleniod valve was closed.

I also think that the flow of the gas itself, probably causes a draw even before TDC of the piston.

With a good exhaust it should, that is why the pairing of cylinders to educt one from the matched pair and the timing of the air column. I have alway wondered just exactly what the pressures are everywhere in relation to crank position. Even looked at some high speed high pressure high accuracery transduces I have but temp was a problem. Was going to put one in the cylinder also. They were $5,000 a piece.

Got me to thinking about wiring it into my lm1. I wonder what he volt is??????

[INDYERIKXX]

to lower emission in exhust gases pumps air into manifolds to lower hydrocarbons.

hints the fucked up air fuel reading on the dyno when it is hooked up.

Erik

[DrDyno]

...This is overlap and the column of air in the exhaust having mass pulles on the droping piston after top dead center when the intake and exhaust are both open. 'This is when the reeds see neg pressure and if the solonoid is open will draw air from the box.

However, I think the valve is only open when the throttle is closed, so to burn the unburned gasses still in the cylinder and crankcase and throttle bodies when you back off the gas.

I have a graph of before and after pair valve removal afr...

I, for one would LOVE to see that graph!

Except for XXQUAD, I think we're all forgetting the reed valves. Seems to me the solenoid can be open whenever it wants to... it's the reed valves that during their opening and closing (based upon cylinder pressure) are the actuators. Negative pressure and they're open allowing air to be drawn from the airbox. Positive pressure and they're closed... no airflow. Ram air effect probably assists the airflow.

The only problem with all of this is: Doesn't seem like it would have effected my idle speed. Vacuum is lowest at idle. Guess I need to recheck my airbox and linkage!

[cbrxxquad]

My pair's are blocked, and I replaced my fuel regulator with a Mr. Turbo, and my idle droped a lot. When warm will idle at 500 rpm,,, well lope. I am sure the fast idle is sticking cause I have seen one of the slides sticking out when it was not susposed to be. I plan on doing a clean and test on the wax unit to see if anything is going on causing the problem. I have just sprayed it with carb cleaner and if it is working I can't tell it. If I raise the idle screw when it is cold it is to high when warm, not badly just not right.

Just info, to think on about the changes that effect the afr readings at idle.

I know some carbs,,,,or throttle bodies,,, have to be almost closed at idle for other systems to regulate fuel and air. Open to much and they are defeated.