Air fuel ratio question
 

Addicted to finding that perfect tune..I picked up a 4 channel wideband and put them in the right bank and also put a 5th sensor in that collector. The header sensors are all located 10 inches downstream. Made a run and The collector sensor reads 1 unit leaner than the header sensors. Just wondering if that's normal, is that fuel still burning on its way down the header? I wouldn't think fresh air is making its way in the collector at WOT.

Re: Air fuel ratio question
 

Bobby, you would expect all widebands systems would report the same air/fuel ratio in the same engine, same run. Would certainly be nice. But, they do not. All we can do is find what numbers, with what we have, that makes our car fastest. Even different sensors often give a little different data, same car, same location. I buy an extra sensor for mine before it is needed.

Re: Air fuel ratio question
 

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.

Re: Air fuel ratio question
 

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.

Re: Air fuel ratio question
 

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.

Re: Air fuel ratio question
 

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

Re: Air fuel ratio question
 

"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.

Re: Air fuel ratio question
 

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

Re: Air fuel ratio question
 

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

Re: Air fuel ratio question
 

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!