JUIC3D

In the battle to legitimately make 500whp cam-only, I added a ported intake manifold and took a trip back to the dyno to make 3 pulls.

No change in tune, the car lost 10wtq and gained 6whp, but the air fuels were quite different in the midband.

I logged all 3 passes and the NGK AFX showed a/fs as low as 11.3-11.5, a far cry from the nice and steady 12.5-12.8 the car maintained with the stock manifold.

How much variance can one expect when comparing widebands?

TurboLX

The upstream NGK wideband should be much more accurate than pretty much anything you're going to shove in the tailpipe.

JUIC3D

That's what I was thinking Greg. Thanks for chiming in.

I would expect the tailpipe wideband to read more lean as well, and it looks like it's about a half point difference than the NGK.

0Tampa Tuning

Yes the tailpipe clamp will be slightly leaner than what you'd see in the header bung especially if you have CATs.

Yes there is a error zone between O2 sensors brands.

triblk6spd

You must remember that calibrating the NGK piece is pretty important too. I would think a freshly/properly calibrated tailpipe sensor would be good as well.

TurboLX

Yes, it's always a good idea to verify the sensor calibration prior to working on a car.

No, I would not really put a lot of faith in a tailpipe sensor. Even calibrated, they are subject to fresh air wash at the tailpipe location. The cats can actually skew the reading *either* direction, depending on what the engine was doing previously. Catalytic convertors act like a "sponge" for oxygen and work both ways.

Ideally, you just want one good quality, calibrated sensor upstream of the catalyst with a controller that does proper sensor temp control and correction. Hopefully, your exhaust backpressure won't be so high as to skew the reading from pressure, but that's usually not an issue with most high performance exhausts.

JUIC3D

Thanks Greg, I appreciate you chiming in. I just bought the Advanced tuning book from Barnes and Noble and am slowly making my way from page 1 to the end.

jim2092

Just switched my Innovate LM1 sensor from my Innovate tailpipe sensor bracket to my header bung and went from AFR's in the 19's to 13's! This is with a high overlap cam but I will not trust tailpipe adapters in the future. LM1 sensors are not the best but as you can see, tuning under these conditions are impossible.

JUIC3D

^ That sounds about right.

I just made 517whp/462 torque cam-only with timing at 24* and fueling in the 12.4-12.6 range. That was off my NGK sensor--the dyno showed much closer to 12.7-12.99

DSteck

Pretty much.

superscout03

or you can just Fab an extra set of headers for tuning only with a wideband on each runner to tune each cylinder =) oooh yeah

USAF-Vette

What book? I'm interested.

Rick

JUIC3D

http://www.amazon.com/Engine-Managem.../dp/1932494421

Ikester

Hi,

Just curious though, wouldnt that mean the LSx tuner shops would need to install the wide band upfront with a bung on each of the cars they tune to get an accurate reading? Im only asking because I notice 95% of the shops ive seen use the wide band attached to the tail pipe. Or can the sensor out back be calibrated for the location?

Zip Corvettes

You just hit the nail on the head. Let me guess the car gets tuned in 3 pulls on the dyno too. You should have your WB as the first sensor in the system followed by your bank 1 or 2 sensor 1. The 02 sensor also has a stream behind it, kind of like comet so you don't want the GM narrow band sensor to pollute the WB. You don't have to weld in an extra bung.
If I am calibrating a car that does not have a bung I remove sensor 1 and install my WB, then I remove sensor 2 from behind the cat and install sensor 1 and shut down the codes for sensor 2. I am only calibrating in open loop so I really do not care what my sensor 1 is reporting, but it needs to be there. My WB has a accuracy of +/- 1.5 % vs the factory of like 8-10%, so I want my WB data to be the most accurate that it can be. If you "tuner" has the ability it is always nicer to install a dedicated bung for the WB.

minytrker

Trying to use a tail pipe clamp for any idle or light throttle is pretty much a waste of time especially on a cammed car. Depending on what type of exhaust pipe and tip the vehicle has I have had it match at WOT but it all depends on the tail pipe and how far the sensor was in there and if it picks up any outside air.

TurboLX

Then 95% of those guys don't fundamentally understand how their equipment works. Mixing fresh air and exhaust (which happens on every pulse that is the sound you hear) dilutes the measurement. Ideally, you want the wideband as close to the engine as possible. Front O2 locations are very good for this (as Justin recommended) as long as there are no other exhaust leaks.