Steve-6.1 Question

[Forzfed]

If you look at the graph the band is from .85v to 1.0v, no?  Isn't the band .15v?

[Scoobum]

I know if I drop below 750 mv's I'll see KR. Makes no difference to me what the AF is.

[earlbrown]

That's a heat thing.   And we all know knock loves some heats.   And even makes some serious heats when it gets on the clock.




When it comes to narrow bands, anything above .450 is 'rich', and anything below. .450 is 'lean'.


If you were to ax how rich or lean, a NB just can't answer that querestion.

[Scoobum]

Okay, it's a heat thing. Below 750 mv's I see KR.

[daveismissing]

Not sure I'm following the heat thing. If you take the averaged/processed voltage pulses from a NB you will see the trend if it is running lean or rich. It just isn't so good/acuurate further away from stoic.

[earlbrown]

When things are going right, it goes back and forth between 'rich' and 'lean'.

A NB cannot tell you how rich or how lean a mixture is. Just if it's greater or less than 14.7.

When voltage deviates way further from .450V that distance isn't an indicator or A/F mixture,  it's an indicator of heat.

[daveismissing]

I stand by my statement. If you look at the *averaged* amount of time spent above the switching point vs the amount of time below you have an indicator of how rich or lean you are. These are the mv we see on the scanmaster.
If it was a pure heat effect why would not we just tune by EGT sensors?

[Steve Wood]

The narrow band sensors are very sensitive with regard to egt and pressure.  Located before the turbo, they are subjected to a lot of pressure and they read differently under boost than they do at cruise at the same A/F...in my experience.

I can say that on my cars, at cruise, 000 on the NB is right at 17-1 on the A/F.  I have gone to 000 and then taken out some more fuel until I got to the point of lean cruise misfire.  These days, I set cruise to read about 010-020 for a hig 15s-low 16s A/F.

We know from experience that 770-780 works well for straight gasoline.  On cars spraying alky, I have seen very low 700's with no detonation but I prefer 750-770 for safety's sake.  I know most people don't agree with me, but, when you spray alky, most of the tuning sensitivity goes out the window...It's a waste of time to fret the tuning on an alky sprayed car.  Those that have ever run a straight alky car know that the power band is very wide on the A/F scale.  I suspect E85 cars are the same way.

I would argue that cylinder head temperature is more important the exhaust gas temperature.  Airplane guys probably agree with this.

At cruise, egt's tend to increase either side of stoich.  That has been stated frequently in the literature.  Here is one such   http://www.enginebasics.com/EFI%20Tuning/EGT%20vs%20AF%20Tuning.html

Under boost, we see A/F's in the 10.8-10.9 range paralleling the 780 or so NB.  When they don't, it's time to look for a problem. 

[Scoobum]

How good/bad were the EGT gauges guys had mounted in the car with the probe in the downpipe that were used years ago. Haven't seen one in a while.

[Steve Wood]

There was some problem with obtaining an interface that would work between the probe and PL as I recall altho they should have worked with various meters that displayed egt.

All the ones I saw, including mine, were mounted in the up pipe to the turbo beside the factory NB.  Drill a hole in the up pipe and mount the probe with a ratchet style clamp just like a hose clamp.

In my opinion, they were a useless fad.  Yes, they gave us average egt but what did we do with it?   Some said we should not exceed 1500 degs for safety.  I don't know what that means.  I still tuned for no timing retard and was always close to 1600 degs. That was a SMC alky set up at the time.

In my opinion, again, the only real use would be on a dyno with one inserted into each header tube a few inches from the head.  Then one could use the results for intake and head porting to obtain even flow and make further adjustments to fuel and/or spark on a per cylinder basis IF one has an aftermarket management system that provides that capability.  That means we could tune to the weakest or the strongest cylinder depending on what our tools are.  Might be worth a horse or two...or not

99.9% of us can't drive the car well enough consistently to avail ourselves of such gains.

[daveismissing]

I think Norbs had a scheme to monitor each cyl but I don't remember if he was logging  or planning to trigger aborts based on abnormalities. When the single vendor stopped making the thru hole large conditioning chip for the sensors most hobby guys abandoned their projects.

[Scoobum]

Norbs had an EGT probe in each cylinder...a certain distance from each flange. He had a gizmo in the glovebox...and it would monitor each cylinder EGT...and then he could adjust it. I don't recall if he adjusted it via the gizmo...or via XFI.

[Scoobum]

The EGT 'gauge' I'm thinking of was about was 6 inches by 4 inches and had a digital readout. You'd have to watch it going down the track.

[Steve Wood]

Yep.... But you could also log them....I think I tossed my meter recently

[daveismissing]

I think he persuade some brainy kid to build a 6-8 channel unit with a processor to monitor and output alarms. I think it lost favor to the vampire per cylinder monitor and retard thingy-which actually seems pretty useful.