I have a pair of headers with AIR tubes, and I intend to keep the AIR injection system intact so the car runs clean. It is a 350 w/ World Products Sportsman II heads, 0.503"/0.510" roller cam, and a holley stealth ram. Should be very strong.

Anyhow, the AIR tubes for the headers hang way down into the header primary tubes (almost all the way to the bottom). Is there a reason they have to be like this, or can I take a die grinder and grind most of the hanging-down tube back up towards the top of each header primary tube? The only thing I could think of was that the tube is open on the side facing away from the engine, to make sure the AIR injection does not wash towards the valves. I think AIR in a log manifold shoots towards the valves though, so maybe that's not it. The AIR tubes are large, maybe 5/16", so the fact that they hang down across almost the whole diameter of the primary bothers me, for HP. I do want AIR to be functional though.

Ill post a pic of what I'm talking about later. I think I took pictures.

 

The theory is you get better mixing when the tube is down in the flow, and the tube doesn't significantly affect flow.

 

Ok thanks for the answer, I appreciate it. Do you know where you got the info that the tube doesn't affect flow much? When people port heads and manifolds they are worried about small casting bumps hurting flow. The air tubes are gigantic compared to casting bumps, etc one might remove porting. Just curious

 

The purpose of the upstream AIR is primarily to heat the O2 sensor. Secondary effect is HC oxidation during converter warm up. The tubes extend into the exhaust passage to enhance the oxidation.

The implementation of a heated 02 sensor can more effectively suit the first function. I have no numbers regarding the effectiveness of HC oxidation with tube extensions versus without. If you have a downstream tube to the converter I suspect the effect on emissions is minimal.

 

All I can say is that I gound my down flush. Passed California emissions that way and yes I do have a heated O2 sensor.

 

My O2 is heated. Hrmrmrmr, thank you Texas and five7 for the technical explanation of why the tubes are down so far, and thank you GTA for the emissions test experience. Although they don't test your car during the warm up phase, they test it closed loop, so if you increased the emissions during warmup, the test won't show that.

 

The AIR pump heats the cat, not the O2 sensor. If it was for the O2 sensor than it would only be on the driver's side, where the O2 sensor is.

 

You did not understand my post, let me elaborate.

I did not say nor imply that the reason A.I.R. exists is to heat the O2 sensor. What I said was that one reason UPSTREAM AIR is used is to facilitate the heating of the O2 sensor.

the air injected by the A.I.R. system oxidizes Hydrocarbon emissions and assists the catalytic converter.

 

I agree with Kevin91Z. When I read it, it "sounded" that you were saying it was to heat the O2 sensor. It's worded kinda confusing.

 

My apologies for your lack of comprehension.

 

When I read that, I take it to mean that the upstream air is primarily to heat the o2 sensor. How else can that be comprehended????

 

Okay. . .

A.I.R. existed before catalytic converter or O2 sensors. Guess where it was attached? Right, just outside the exhaust port in the exhaust manifold. Why? Because the exhaust is hottest there, and the extra O2 has the greatest effect oxidizing unburnt fuel.

It is diverted to the cat so that it 1) won't affect the O2 sensor, and 2) because in closed loop the cat is the hot part, and 3) because the extra O2 is more effectively used there.

Don't forget that some systems divert A.I.R. back to the manifolds during certain closed loop conditions. Now, why would that be???

 

I was under the impression that it switches back and forth in closed loop so that neither the cat or the O2 got too hot.

 

Never heard that. Seriously doubt OBD I would.