One Lap of Lime Rock through the eyes of an Oxygen Sensor

[Jeff Higgins]

Agreed, John - too rich can be damaging as well. It's just a matter of where the "too rich" range that actually washes cylinder walls and dilutes oil begins. I would posit that in the range we are discussing, we have not yet gotten down into the A/F range that would cause that kind of damage.

Boosted applications will run even richer than what we are discussing. MFI atomizes fuel more thoroughly than just about any other induction system, thereby facilitating a more complete burn of a richer mix.

In light of that, I would be curious to see if anyone has conducted any sort of a conclusive test aimed at determining where "too rich" begins for our motors. Myself (and others) have inadvertently run the "too lean" test not only in our motors, but across the entire motorsports spectrum with (rather disappointingly) consistent results. The damaging affects of "too lean" are quite well known. "Too rich", to my knowledge, is not nearly as widely known. I would be curious to see something on that.

[Walt Fricke]

Well, not a hint of black in my tailpipes, so I don't think I am running "bad" rich.

The selection came shortly after the start of the race, so that may explain why some of the shifts are less than 7,800 RPM. This got more consistent as the race went on and the field spread out some. Now to hunt up the formula which will allow me to calculate average Gs accelerating (and braking) from point to point. For instance, 6.47 seconds to go from 52.2 mph to 94.3 mph. Knowing the car's weight, maybe I could also calculate roughly the horsepower or torque (ignoring rolling resistance, and air resistance)?

Hallett is not the best track for this kind of calculation, as it is just about all either uphill or downhill. On a flatter track, or one with flatter portions, I can tell from the RPM trace which gear I am in - 2d is steeper than 3d, etc.



I still don't understand why, at WOT, the unsmoothed AF trace jumps around so much. I'm reading the right bank just after the collector, but I don't think the sensor is going to react to each separate exhaust pulse.

Or why the gizmo won't recognize the SD card when inserted.

[304065]

Walt, the sensor actually does react to each individual pulse, it's that good. If you look at the photo of the LM-1 in this thread and read the commentary you can see that the flickering bar graph is actually reacting to individual exhaust pulses. That's on a single bank of three cylinders at idle, but it's pretty good.

LM-1 Installation in Early 911- MFI

Anyway, thanks for putting the blue and red lines on the graph. It shows that the WOT enrichment in your system is working well- the mixture starts off at about 13:1 and goes richer as the RPM trace climbs. That's what you want- it shows that the fuel pressure and injector size are all up to snuff. That's pretty consistent in the first couple windows. Then later, are you feathering the throttle to stay on a guy's bumper? That would explain why the mixture is going lean.

All this explains why tuning is best done on a dyno-- you can set the RPM at a rock-solid number and then tweak the AFR and ignition timing until the engine speed increases, implying more torque.

You know who we really need? Steve Weiner. I'm going to ask him to describe the way he dyno tunes MOTEC for max performance. I, like you, was trained by a blind woman with a sword . . .

[Walt Fricke]

I did use a dyno. I took the program the previous owner of the engine used with 40mm ITBs, and took it to the track. Had some issues (most notably due to the TPS showing lower voltage as the throttle was opened a bit, as in entering the track). Went to local dyno. Showed leaning at high RPM. Got scared. Trailered a couple of hundred miles to Allan Johnson in Grand Junction, Colorado. Fixed the miscellaneous problems (including refurbished larger injectors which were all stuck closed), and tuned as shown here. Expensive work (made 10 times more expensive when my truck's fan flew apart and took out the radiator on the return trip). His philosophy for race motor tuning is no TPS/MAP blend, and two dimensional maps.

I have had the habit, during the pace lap, of warming my brakes at times by using gas and brake simultaneously. First time I tried that I stalled! Most embarassing. Not sure quite why.

I have used my netbook computer for tuning. Turns out the screen is too small, and some of the useful commands are hidden under other bits. Afraid I will have to purchase one with a 14 or 15" screen. On it goes. However, the throttle response improvement is worth it all.

[dicklague]

If you are serious about AFR instrument, look at the Daytona-Sensors one offered by our host. Records up to 2 hours of data, AFR, RPM, and another input like vacuum/boost.

I love mine and it has really helped me fine tune my MFI.

Very high quality and one small instrument.

[lupin..the..3rd]

Originally Posted by dicklague

If you are serious about AFR instrument, look at the Daytona-Sensors one offered by our host. Records up to 2 hours of data, AFR, RPM, and another input like vacuum/boost.

I love mine and it has really helped me fine tune my MFI.

Very high quality and one small instrument.

Got a link to the product? I don't see it.