NHRA686

You could put a www.gzmotorsports.com vacuum pump on in place of the air pump and gain some power.
https://www.gzmotorsports.com/VP102-vacuum-pump.html
https://www.gzmotorsports.com/VPP403...p-pulleys.html

aklim

I don't care what you do on the passenger side but on the driver side is the O2 sensor. The Check valve is a 1 way street so it will allow air to be pumped in and hold back exhaust. I really would remove the valve and cap it off with some pipe cap from Menards or Home Depot.

Or used for something useful like maybe a heated O2 sensor?

TheBlaster9001

I don't think that the O2 sensor cares about the AIR system, since the computer isn't looking at the sensor while the AIR is blowing in the headers. Otherwise, you'd get a check engine light out of it.

Curious, how would you use the AIR delete to heat the O2? Am I missing something?

aklim

I think the AIR system blows air into the exhaust manifold at the start of the cycle and then switches to the cat after closed loop? Supposedly to mix it up since the cat is still cold and it needs temperature to operate? http://www.superchevy.com/how-to/add...-clean-living/

IF it has a constant 12V, the heater in the heated O2 has a 12V requirement. So... I think that is what I did. Either that or some other emissions stuff. It's been a while.

TheBlaster9001

Ah, my car does not have a heated O2, it is still the one wire. I figured the ceramic headers will get it hot fast enough without having to run wires and buy a new sensor.

I think that the pump only dumps in the headers under acceleration, and that it's sole purpose in that position is to let unburnt fuel continue to burn. I don't think it changes the AFR in the manifold by much, since no trouble codes result from removing the pump.

Previously I had thought that it only pumped in the headers when the 02 sensor was not being used, since the car would trim based off of how well the pump was doing. The pump air isn't metered at all, and the pump isn't 'tuned', so I think the car would over-trim when air entered the header, despite it not needing to. I could see AIR dumping in the header anytime the 02 is ignored (WOT, and while heating), but otherwise I don't see an advantage for that design (advantage in this case is less fuel use/less emissions).

aklim

AFAIK once it starts the system dump fresh air into the manifold Once close loop is established the air gets diverted into the cat. This way it does not interfere with the O2 reading. In close loop it reads O2 sensor but in open loop, it does not.

Under WOT conditions it does not care about the O2 readings since it is going off the preprogrammed tables

TheBlaster9001

Yeah, that's what I had thought. I do remember the shop manual said the air is injected in the headers at WOT, and is not injected in the cat during decel.

aklim

I can't remember what I was doing since it was a long time ago but either I use AIR or the evap canister for my heated O2 sensor. IIRC it was closer to the stock manifold than the current location. I believe people have used a heated O2 because the header flows better and is cooling down the exhaust so sometimes it is too cool and the O2 sensor drops out since it needs a certain temperature to function Hence it has to be in open loop until conditions are right one of which is the sensor is sending reliable data

TheBlaster9001

Huh, I've never heard of doing that.

aklim

https://www.corvetteforum.com/forums/c4-tech-performance/2245461-heated-o2-sensors-are-they-absolutely-necessary-with-lt-headers.html

Makes sense since the sensor is farther back and the walls are thinner plus there is less pressure since that is what headers do. If the exhaust charge is cooler then the O2 sensor gets cooler and might fall out of loop

TheBlaster9001

Hmm, there might be merit to that in some cases. Perhaps because my headers are ceramic coated, but I saw exhaust manifold temps increase after long tubes. Losing AIR might also have something to do with that. I haven't had issues with dropping out of loop, but I have noticed a change in smell and backfiring after WOT pulls, which would point to needing a tune to accommodate the long tubes.

aklim

Not sure I'd be curious to see what happens after getting a tune. I hope you have the intake change done before you tune.

TheBlaster9001

Yep, Lingenfelter top end. The headers were the last part of the engine to be modified. I'm very happy with the setup now, going to swap ECMs and start dialing in a tune this weekend.

aklim

Keep going. 383 will be next. Don't opt for the high compression heads. Blower next

TheBlaster9001

Already is a 383! Compression is about 9.5, forged lower end. I've thought about a blower, but that'll put me in the car more than it's worth, which I don't want to do.

aklim

I blew the LPE short block using cheap TFS heads. This time the long block was ordered with AFR190. I'm into a couple motors so the car costs more than it was worth and I have to run out the clock to get a new one.

vader86

The AIR dumps into the exhaust manifold at startup to light off the precats with good oxygen, before the O2 sensor has reached the ranges for closed loop operation. After that the AIR is pumping into the primary cat.

Headers will cause the car to drop into open loop at idle at most stop lights, I watched it first hand, even on very hot summer days. This caused my main cat to clog up so I eventually cut it off. Whether you change to a heated O2 is up to you, I did not, but you won't drop out of closed loop if its on there.

aklim

You know if the solenoid wire is always hot waiting for a ground signal? IIRC they were. Thanks Car not back yet from the body shop.

Shorties should not since the sensor sits close to the manifold and aren't that good at relieving pressure or am I lookin at it wrong? BTW did you keep the pre cats? I suspect not. Did cutting off the main cat make the noise worse? Seems like that to me which is why I replaced it TIA

vader86

Shorties shouldnt make much difference if bolted to a stock or semistock (w/o precats) front Y. The pressure will remain higher and hold the heat there. O2 needs to pass the startup timers, plus reach a temperature range above 600F (as i recall) to read voltages that the ECM will decide are good for closed loop and then useful for fuel trims.

I use longtubes, the extra pipe diameter will scavenge that hot gas out, even if ceramic coated to keep heat contained. Unless you must pass emissions + visual, I'd never use shorties.

Removing a main cat deepened the resonant drone and widened the resonant RPM range.

corvetteracer72

This is getting interesting ...

Sorry for the stoopid question , but what happens if the car drops into open loop ?
I just got a pair of Hedman's and I am about to ditch the air sistem and install the headers .

Also I've seen that those heated sensors have 2 wires . My 85 has only one .
Any ideea on where to plug the second sensor wire ?

Thanks.