[Hatch]

Ummm....I'm having some space issues trying to fit a 4.3 into a Sami frame. Anyone know if you can buy a kit or parts to build your own headers? It's the exhaust manifolds and exhaust pipes that are causing my headaches. Mudlug suggested dumping the exhaust outside the frame.

On a related note: does the O2 sensor need to read all cylinders' exhaust, or will it function properly reading just one bank?

 

[Hatch]

Hmmm

 

[Hatch]

Google is a wonderful tool
http://www.carcraft.com/howto/0304_head/

 

[54inches]

It can operate off of one cylinder, but if you have problems with that cylinder then the computer will lean/richen the whole bank and that can be bad, whereas, if you are getting a reading from all cylinders the reading is a combo and therefore if one cylinder is lean/rich the computer will not have to lean/richen as much because the sensor is reading an average of all the cylinders in that bank. Make sense?

You could get a O2 simulator and not have to even worry about it, but that wasn't your question....

 

[Hatch]

It can operate off of one cylinder, but if you have problems with that cylinder then the computer will lean/richen the whole bank and that can be bad, whereas, if you are getting a reading from all cylinders the reading is a combo and therefore if one cylinder is lean/rich the computer will not have to lean/richen as much because the sensor is reading an average of all the cylinders in that bank. Make sense?

You could get a O2 simulator and not have to even worry about it, but that wasn't your question....

I got it. So if I were to end up with dual exhaust, I could put the O2 sensor on just one side (3 cylinders) and be okay. Maybe not the prefered method, but it would be okay. It's just TBI, so it ain't like each cylinder gets it's own supply of fuel.

Anyhoo, doesn't matter til I fit the engine into the frame

 

[54inches]

You got it! If it is setup for 2 sensors then use both, more data=more accurate readings=happy computer.

 

[4x4Freak]

The stock setup only reads off of one bank anyway.

 

[Hatch]

The stock setup only reads off of one bank anyway.

O2 sensor is right AFTER the "Y" in the y-pipe that came with my engine.

 

[4x4Freak]

Ok, its different from the V8s then.

 

[Hatch]

Maybe 3 cylinders ain't enough to get a good reading (from the factory's standpoint)?

 

[Whifflebat]

You might be able to (im not totally sure), but put the exhaust manifolds backwards, and run the exhaust forward, down, and around to the back. Thats what we're doing on our healey and it looks like its going to work great.

 

[afroman006]

You could get a O2 simulator and not have to even worry about it, but that wasn't your question....

Wrong. The TBI system uses the O2 sensor to adjust the fuel mixture and you simply cant duplicate a dynamic reading of that sort.

Now on later model Vortec engines (Chevy's at least, I'm not familiar with anything else), they have 4 O2 sensors, 2 before the cats and 2 after. On these you can replace the after-cat sensors with simulators if you are running without cats, but that is the only application for O2 simulators that I know of.

 

[limey]

If you want to make you own exhaust you can always weld a bunch of soup cans together. That should give you 3” exhaust.

 

[54inches]

I disagree with you afro. Too much greenery in your diet.

 

[Hatch]

You might be able to (im not totally sure), but put the exhaust manifolds backwards, and run the exhaust forward, down, and around to the back. Thats what we're doing on our healey and it looks like its going to work great.

Hmmm. I'll look at that. But off the top of my head, I'm thinking the accessories hanging off the front of the engine are going to be in the way.

 

[afroman006]

I disagree with you afro. Too much greenery in your diet.

Let me ask you this, if you removed the O2 sensor from a TBI engine what would control the fuel mixture? On that note, I challenge you to find a company that makes O2 sensor similators for TBI engines.

 

[Whifflebat]

I gotta agree with afro

The 2 02's on the back side of the cats on a vortec are there simply to tell the engine that the cats are working, no more no less. They can be replaced with simulators that put out a signal that says the cats are working. However, on the front side of the cats, the 2 o2 sensors read the exhaust and the engine uses those readings to decide on how to adjust the fuel mixture.

On a tbi, the one 02 sensor before the cat tells the engine everything it needs to know on how to adjust the fuel. This is why when the 02 goes bad, the gas milage goes to crap. Take out the 02 sensor and the computer will be running blind, and it will run, but your gas milage will be bad and you'll suffer a power loss, aka "limp home" mode.

Yeah thats true Stretch, er hatch...dangit..., our healey doesn't have much in the way of accessories on the front, just an alternator.
Here's a picture, not of ours though, you can see it on the right side.

 

[Hatch]

4.3 GM V6 exhaust ports are assymetrical front to rear. Flipping the exhaust to dump in the front is not an option. I then looked at swapping the manifolds from one side to the other and exiting up instead of down. I think it would be too close to the firewall to manage the ducting.

I'm not giving up yet.

Thinking out loud:
So if good old cast iron exhaust manifolds are NOT the same tuned length for each cylinder, how detrimental could it be to build/use NON-equal length tube headers and let each runner go wherever I need it to go?

 

[54inches]

No your wrong.