WB accuracy

[Rickerbucks]

I just came from the dyno for the first time. The WB in the tail pipe was about .6 higher then the FAST results.

Is this normal?

 

[bobc455]

I've heard some people say that the WB can show slightly inaccurate readings under heavy boost or with lots of nitrous.

On the other hand, I have two identical thermometers outside my house- right now one is showing 71 and one is showing 74. I also have a scale at work that shows me weighing 213, and another one that is 209.

What's really important for you is that the sensor is consistent- if your sensor shows 11.8 when you are actually at 12.2, that's really not a problem as long as it shows it that way every time. That way the tuning will be consistent, and when you try going richer or leaner, the car will respond consistently.

-Bob Cunningham

 

[Rickerbucks]

TY Bob

The car FEELS good so I'll contnue as normal for now.

 

[Craig Smith]

Anymore I would say this is "normal" for lack of a better word. It seems like a common scenario to have a chassis dyno O2 sensor read quite differently than the FAST sensor.

 

[NoSlix]

This is normal. Put the dyno WB in the same spot as the FAST sensor and it will be MUCH closer. We usually see .5 difference in AF when using the tailpipe monitor. Compared to the $5000 Horiba WB's we used to use, the FAST was pretty close. Generally within .2 when the sensors were mounted in the same place.

 

[Rickerbucks]

So I should just continue o tune for the FAT wideband then.

Another question. I know that detonation is from too much timing and the the car breaks up and makes a ratteling noise.

What if you have too LITTLE timing? What is the symptom? I ask because at the dyno, at about 4800 rpms the car starts to stumble and the power drops off very quickly. Looking at the Log and the tune, it appears that this stumbeling occurred when the timing went from a "28" degree cell to a "24" degree cell. I think I had about 8# of boost at the time and IAT's are about 90 degrees. I suspect I have to must retard so I'm curious for some opinions before I advance the timing and melt things.

PS: the dyno operator said there was no hint of detonation.

 

[Toma]

I was dyno tuning a FAST equipped 88 vette today for about 8 hours, and found that at around 14.7:1 my dyno WB and the FAST wideband were within .3 BUT the richer the mixture, the discrepency grew. At 12: 1, the fast was reading 11:1, at 13:1, the fast was reading 12.4.... so it seems to grow with increasing richness....mindye the customer had it mounted in only one header pipe, and I was sampling in the tailpipe....

 

[Rickerbucks]

Well went for street testing and the timing change HAS improved the power but still have the stumbeling at the high end of the revs. It must be a spark related issue. That being said, the AFR is still fine even when it is breaking up.

I think I'll change the coil first. MSD box second. Close the plug gap next - currently 35 thou - and finally the opti-crap.