Dyno help-where to measure air-fuel

[Derry]

The car is in having a baseline dyno done b4 the whipple installation. Is thre a pre existing port somewhere in the exhaust system or do you just weld one in for accurete measurement? Any help is appreciated.

Derry

 

[427Aggie]

Most of the ones I have seen have a braket and secure the O2 sensors on the exhaust pipe...you shouldn't have to plug into anything.

As the saying goes just stick it up the tailpipe

Matt

 

[Fubar]

I pulled the O2 sensor just before the cats on the Driver's side.

Leave the factory O2 sensor plugged into the wire and just set it off to the side. If you disconnect the O2 you will get an engine light error. That can be reset by disconnecting the battery for a few minutes.

 

[Derry]

Mmmm, I am under the impression that the cats alter the gas composition by their very nature and that you would have to measure b4 them unless there is a known correction factor or something?

Derry

 

[barondw]

Derry

IMO you are correct. Generally you need to install a bung which the O2 sensor is inserted through. It requires someone with a cutting torch, the bung connector and a welder. Placing a O2 sensor in the exhaust does not give a true reading.

Dave

 

[Fubar]

Derry

IMO you are correct. Generally you need to install a bung which the O2 sensor is inserted through. It requires someone with a cutting torch, the bung connector and a welder. Placing a O2 sensor in the exhaust does not give a true reading.

Dave

Whoa.. no torch needed. There is an O2 sensor BEFORE the cats. Just pop the hatch and look from the top. It's easy to get to.

I've got my GT here today. I will post a pic in a few minutes.

Most Dyno O2 sensors will fit in this hole.

 

[Derry]

If I pull the existing O2 sensor, wouldn't the engine management sense this and go super rich?

 

[Fubar]

If I pull the existing O2 sensor, wouldn't the engine management sense this and go super rich?

This is exactly what I thought. But apparently when the engine is in a high load situation it goes into "closed loop" (I think that’s what it's called) and manages the engine based on pre-programmed figures.

So basically, good question, but no it would not affect the A/F.

 

[barondw]

the reason to put in a bung is so that the Dyno shop can take out the plug, put in their wide band (very expensive, very accurate) O2 sensor and gather accurate information about the fuel mixture. Then when all is done they screw the plug back in and your off to the races.

Dave

 

[BlackICE]

the reason to put in a bung is so that the Dyno shop can take out the plug, put in their wide band (very expensive, very accurate) O2 sensor and gather accurate information about the fuel mixture. Then when all is done they screw the plug back in and your off to the races.

Dave

Can they use the bung used for the stock O2 sensor in front of the cats, since they are tuning for only for open loop?

Also do people use 2 wide bands for the left and right sides, or assume that they are the same. I know the best would be 8 wide bands with EGT probes too, but I guess that is asking for too much.

 

[Fubar]

That's what we did on my Dyno run. The shop just popped the factory O2 sensor and put in their Dyno O2 sensor. It seemed to work fine.

 

[Derry]

Thanks everyone! Fubar, makes sense now in open loop.

Derry

 

[Fubar]

Also do people use 2 wide bands for the left and right sides, or assume that they are the same.

We only used one side. If it's available to you, I would do two. You can't have too much information.