For those out there using the Innovate LM-1 this meter is digital and does not care where stoich is. It gives you a linear reading and can be switched from AFR to lambda and back.

You need to know what Stoich is for the fuel your tuning for so you know where your target is.

Neal

 

No you don't. Read the previous posts again and think about it.

 

It is most interesting to compare AFR and intake vacuum (or MAP) in modern GM engines. With a Gen 2 SBC in my '98 GMC Savana, I was surprised to see 14.7 AFR maintained down to approximately 3" HG of vacuum. For those who have never driven with a vacuum gauge in their cockpit instrumentation set, this means that stoichiometric ratio is maintained to nearly WOT without fears that pistons will burn or self destruct - contrary to the fears of the nervous.

For those so interested, one can find instructional articles written by former airline pilots on how to lean the old piston engines to run very lean (50 degrees lean of peak EGT) continuously in order to get the required range for their aircraft.

In a car, when you think about it, lean AFRs really are beneficial for cruising mileage especially when one realizes that the vacuum levels are so high when cruising at 70 mph (15 to 19" Hg), that detonation is not a problem. If you don't know, a vacuum level of 15" is equivalent to WOT at 18,000 feet above sea level! Provided that surging or misfiring does not exist, I would have no problem with running 16 or 17 AFR for cruise. Of course, the other side of the problem is to transition seamlessly to the rich side when adding throttle as vacuum drops through the range of 5 to 12" Hg; finally, at WOT, I like to see about 12.8 AFR.

 

Over the last several months I've been working on a mix issue on my own moderate build LS6 crate motor. We installed the motor in the car in 1977 and the motor has about 10K miles on it. I pulled the DP about a year ago an put on a Holley SA. Since then I've done about 20 dyno pulls trying to figure out a particular problem with the A/F mix, which I have done. The problem was with the secondary vacuum diaphragm, but not a leak. That's another story.

The dyno shop has "dyno days", and having attended several, I've watched over 100 dyno pulls over the last year. This link goes to a pull I just posted on Youtube. It's not my car (as I haven't had a chance to do my car since I solved my carb problem), it's a friend of mine's "tuned" 2012 Mustang GT. It's hard to see at the end, but the peak HP was around 417. In any event, forget the power numbers and focus on the A/F bar at the bottom, as the operator is warming the motor prior to the pull. During that time, the bar at the very bottom is yellow. When the pull is made, it turns to green and reads "Sample". That's when, and only when, the throttle is at WOT. You'll see that the pre-sampling mix read is all over the place. When he goes to sampling, most of what you see is green and blue, green being "ideal" and blue being "rich". My friend is actually running rich and he knows he needs to work on that.

Every pull I've seen, injected or carbed, is like this during the pre-sampling warm up, which is just "cruising" the car. Basically, if you get the WOT where it should be, the rest is mostly irrelevant (unless you've got some other problem). The only cars that I've seen run below the 12.5 threshold on a consistent basis, intentionally, are the blown cars, but they always do. As I said before, I think if you run sub 12.5 you're going to be too rich and the time you spend on the street will foul out your plugs and chambers. That's why I said read your plugs. After awhile, you'll probably see that's the case.

You're trying to figure your situation out taking "snap shots" of your gauge. That's a tough way to do it, because you're losing the dynamics. You should dyno the car if you can, and if not, watch this one carefully.

http://www.youtube.com/watch?v=s7j_M...ature=youtu.be

 

Maybe I'm missing something but here is the info straight from the manual for the LM-1;


1 Overview
The LM-1 is a stand-alone Wideband Controller used to measure the Air/Fuel Ratio (AFR) or Lambda for an engine. For gasoline-driven engines, the theoretically optimal air fuel ratio is 14.7 pounds of air for every pound of fuel. At this ratio, theoretically, all available oxygen in the air combines with all available fuel. This ratio is called the stoichiometric ratio.

Stoichiometric for different fuels are as follows:
Gasoline 14.7
LPG (Propane) 15.5
Methanol 6.4
Ethanol 9.0
CNG 17.2
Diesel 14.6

The measurement Lambda is the actual air fuel ratio over the stoichiometric ratio. A Lambda measurement of “1” equates to the air fuel ratio of 14.7 (for gasoline engines). When Lambda is less than 1 the engine runs “rich”, i.e., unburned fuel exists in the exhaust stream. If lambda is greater than 1 the engine runs lean, i.e., free oxygen (02) is present in the exhaust. Depending on the engine, maximum power is typically delivered when the engine runs slightly rich (for example
at lambda values of 0.8 to 0.9 for most engines). This instrument provides a means to measure the actual air fuel ratio or lambda in the engine in operation directly from the exhaust. For this a special wide-band oxygen sensor is used to measure the lambda value derived from the oxygen content (or lack thereof) of the exhaust gases

Neal

 

I appreciate the value of a dyno run and have done so in the past. However, for me, I wanted to tweak my A/F ratio more than I wanted to pay for dyno runs. An A/F gauge allows you to constantly monitor your fuel ratio during real world driving. The warm up period on a dyno is just that, a warm up period. Your a/f ratio will be different once the car is at temp than it will be when it is getting to temp.

I think you may be underestimating the usefulness of an a/f gauge and I disagree that if you get WOT right the rest is irrelevant. If you are going to drag race only, then WOT is your primary focus. However, as a street driven car, there are other areas of interest such as economy during cruise.

These numbers represent different circuits and different conditions and I am simply trying to optimize each circuit for each condition.

Idle - 13.2ish
3rd at 2k cruise - 13.7-14.2
4th at 2k cruise - 14.2-15
WOT - 12

I am happy with these numbers. I may see WOT for a few seconds at a time while entering the freeway so i am not too worried about fowling the plugs.

 

Please get back to us on that after a couple of hundred miles. For myself, I'd be interested in seeing a pic of a plug tip.

 

Neal: I may have misunderstood what you're trying to say. It sounded like you you were claiming that by being "digital" the LM-1 in some magic way knows what fuel you're running?

The LM-1 is still a lambda meter. It multiplies the lambda value with a constant to calculate AFR.

The LM-1 config software lets you specify that constant so you can make it read correctly for different fuels. So if you run something like E85 you can set the AFR constant for it and then it will read ~9:1 @ stoich.

Maybe that's what you were getting at?

 

The LM-1 displays output as lambda IIRC. Please re-read my earlier posts on the subject. The values they gave you are distracting you from what their devices do.

Basically, Lamda 1 with fuel = 14.7. On a wideband that displays in "AFR", when the sensor reads lambda 1 it multiples by 14.7 to get the value. If you were running 0.85Lambda, the gauge would read 12.5. It is not ACTUALLY 12.5:1 AFR if you're running any ethanol blend.

It's just a scaled value that I think most people read more easily. The problem is that both the sensor and gauge are completely unaware of the input fuel and thus there's no real way to properly convert to AFR.

For all of those AFRs you listed, the typical wideband will report lambda 1. If said wideband displays in "AFR", it will then scale it to an AFR for pure gas, not knowing what fuel you're actually using.

Remember, an oxygen sensor is exactly that, an oxygen sensor.

You would need a separate fuel sensor that reported data back to your wideband controller in realtime in order to get a real AFR reading, and not "AFR".
A couple of hundred drag strip passes and it might be a little black. A couple of hundred freeway miles and it will be cocoa. Why are you ignoring the fact that it's at or *slightly* richer than stoich for the bulk of driving duty?

 

The LM-1 displays both Lambda and AFR at the same time while turned on. The multiplier for the calculation can be changed to whatever you want through a custom table or you can select one that is already in the program to match the fuel your running.

Neal

 

Cool. It's still better to go off lambda. E85 isn't always 85% ethanol, etc.

Definitely a neat feature, but once you learn to ignore AFR and just go off lambda you'll be better off. My FAST wideband just assumes pure gas to scale against.

 

Have been following threads on this subject as I have newly installed an AEM meter and am trying to understand what I am seeing before modifying anything in the carb. Basically my question is: "are the only readings that count those taken where the motor is actually doing some work?" I.e. accelerating or pushing air aside. Reason I ask is that when ever I let off the gas, the meter goes full scale or so. I assume that is because there is lots of A but very little or no F. And that is OK, right?

 

So called "overrun" (closed throttle, decelerating) doesn't much care about the fuel mix. You don't want it pig rich as it could flood or foul plugs. Going very lean is fine. New EFI cars usually shut the injectors off completely during overrun.

 

That's what you're seeing in the dyno video I posted, and it's what I've seen in the 100+ pulls I've watched. It's where I disagree with the OP. At cruise the engine isn't under much load and unless there's something else out of whack, most readings at cruise don't me much as far as I've observed and learned. It's when the engine in under load that it's at risk and is when you have to be sure the mix is good. My car has run at a sub 12.5 ratio, and the plugs were "black". I just think 12 is too rich as will be shown over time; my goal is 12.5 to 13 in the stretch between 3000 and 6000 rpm. In all the dyno pulls I've observed, too, no one has ever even mentioned their off WOT readings. The operator just shrugged his shoulders when I asked about them, a long time ago. There's technical explanations, but I have no intent on being drug into that. Theory is great, but observation is simpler.

 

If all you care about is drag racing, go for it. If you're going to put most miles on the street, and unless you car is different that a lot of others, down in the 12 range your plugs are going to be black and you may be washing your cylinders with gas. But I really don't care, actually. If your car runs good with black plugs, fine.

But you might want to search a little on where the most horsepower is produced....towards the rich or the lean.

 

The problem with your post here is that the OP *has* mentioned his cruise numbers and they're well into the 14s. I'm not sure why you keep ignoring that?

Were you running 12.5 everywhere or 12.5 WOT? 12.5 everywhere is not a good idea.

You answered that in your other post. 12.5-13 is *about* where the best HP is produced in a NA motor. The only way to know for sure is with some kind of performance metric (dyno/strip) to compare against.

Bore wash isn't a concern at 12:1, esp for a couple of WOT passes. He'll be spending most of his time around the mid 14s, as his post evidenced.

 

I think I understand your point now. I think you are recommending to shift my focus from the "too lean at cruise" vantage point and work on getting the wot numbers in the 12.8-13.2 range. I agree.

I plan to jet down in order to get the wot numbers up and then adjust the corresponding lean cruise numbers down by raising the APT screw.

 

Even though it was 106* outside today, I couldn't wait to go for a test drive.

I went from 71 jets to 69 jets. About a 6% metering area reduction. While cruising around I stopped twice to make field APT adjustments. I ended up about 1.5 turns out from where I started with the APT.

In 3rd gear between 2000 and 2500 rpms which is around 45-50 mph, the A/F ratio was bouncing right around perfect 14.7. In overdrive it went just a touch leaner, maybe around 15.2 at 70mph.

Now, to get the WOT reading, I went to a large hill by my house. Its a good place to put a lot of load on with out gaining a lot of speed. So I went from 2000 to about 4500rpms and the highest A/F reading was 13.2 . I think it was bouncing between 12.5 or 12.7 - 13.2.

I think the car is running great. Wot is in the safe zone now, the car stayed at 180* despite being way too hot outside and I finally resolved my hot start issues as well.

I am pretty impressed with this Quadrajet and the APT design.

Cheers.

 

 

Congrats.