Air fuel ratio question

[west coast]

Hey Bobby i just use the # as reference and move your target richer or leaner and go off the time slip at what it likes. I tell people how lean i run my car and cant believe i don't have holes in the pistons. ever sensor is different.

[Signman]

Bobby
Would think that either and both can be happening.
If your rich fuel can be burning in the primary tube making the O2 see lean. Even at wide open throttle fresh air can get sucked in the collector.
Another variable in addition to the difference in each O2 sensor you're using a 4 channel WB assume it is a stand alone device, the 5th is being monitored by a separate device WB or EFI can also add to the variable.

[randy wilson]

Originally Posted by west coast

Hey Bobby i just use the # as reference and move your target richer or leaner and go off the time slip at what it likes. I tell people how lean i run my car and cant believe i don't have holes in the pistons. ever sensor is different.

I agree with your theory. However lately, like the last 12 years, all 3 engines we ran locally are 3 size jets larger then when just off the dyno. Plugs look almost black, but cars are quicker. One size bigger, we slow down, one size smaller, we slow down. Looks way rich, but quicker by enough to warrant the change.

[Ben Holt]

To answer the OP's question, yes, that is correct. I have found that the farther away from the exhaust port the leaner the number reads. I have seen it to be somewhere between .6 to 1.0 on the AFR ratio. The 02 closer to the port is what I believe to be a more accurate number of what the engine is running, but the collector is a good number to have a reference to make sure the two banks are running fairly balanced to each other

[Ed Wright]

"Closer to the port", in a primary tube you are only seeing that one cylinder. If you have not tested with 8 widebands, you might be surprised at different the others could be.

[Ben Holt]

Yea, I have tuned quite a few engines with 8 o2's, and it is quite the eye opener to see what each individual hole does. But once you get them fairly balanced, then see those collector numbers come into balance as well, it's amazing how well the engine runs, especially up top

[Ed Wright]

If you use a FAST XFI system, you can use a distributor with a cam position sensor & put it in Sequential mode, and adjust each cylinder's air/fuel & timing. There is some power there. Could be suprising the difference in air/fuel ratio you see between cylinders. Change intake manifolds, you get to do it all over again. With my Hogan, I had less variation than with the single plane & elbow. More difference between the 2 tune ups than just that.
And, I saw VERY little difference between my air/fuel ratio in the primary tube O2s, and in the collectors. I must be doing something wrong. LOL

[Ben Holt]

I didn't say that......I just said I have seen somewhere between .6 an 1.0 difference between the port and collector o2. Every combo is different. The OP just asked if the variation between the two is common. My answer is yes, it is common. But from what I've seen, once you get all 4 holes in the bank balanced out nice, the collector number starts to come around, as well, like you have found

The sequential EFI stuff is really neat to fine tune the individual holes. I have really enjoyed messing with that, sounds like you have, too!