Have been using an Innovate LM-2 to dial in a carburetor on my good old Y Block, they work great. One thing I'm a little unclear on though, is how AFR is displayed or measured. I've read that it doesn't matter what fuel or fuel blend is in the tank, 14.7 displayed is stoichiometric for example, regardless. How can this be? I understand that the O2 sensors only read residual oxygen in the exhaust. (So it's akin to looking at your piss the next morning to figure out how much beer you drank.) But if the AFR displays 14.7, that is "stoich" for pure gasoline. Stoich for E10 however, is about 14.1 So it seems to me I'd need a correction factor, or I'd be too lean after tuning with pure gasoline, and then running a tank of E10, which may even contain considerably more ethanol than that, as tests show. See where I'm goin' with that? The Innovate unit does have different fuel menus, though gasoline is the default - methanol, E85, Propane, etc. So what gives? If it doesn't matter what fuel or blend is in the tank, why do they have a fuel menu?
I seem to recall that they went to E10 fuel in non-compliance areas, to make all those cars that run a bit rich, get leaned out, and reduce CO emissions. And it doesn't lean out the other cars enough to make them start misfiring, which would raise HC emissions. but I could be wrong. Yeah, stoich is lower for gasahol, than for gasoline. But all my old carburetors seem to run quite rich anyways. I've only seen one of them ever get into the 14s, that was a stock smog era Qjet.
Yep, I was able to lean out the highway cruise by quite a lot. But this also required hogging out the pvcr's slightly, to bring the wide open throttle ratio back down from being too lean. So the question is, do the numbers displayed on the screen need no correction with different fuel blends, or is it WYSIWYG? 12.5 for example is a little (maybe) on the rich side for wide open throttle, but I'm using non-ethanol fuel for tuning purposes. Is it "really" 13.0 if running a tank with corn squeezins? When I'm on a road trip, there's no way I'll have that **** hooked up, and it will likely be E10, not a huge deal really, it's still in the "safe" range. Guess it has something to do with the way wideband O2 sensors work, they work on the principle of Lamda = 1, and then convert that into numbers people want to see. But then why does the unit have different selections for fuel type?
This may/may not help, but this is from my build thread, and is a table I made to convert the gasoline AFR readings to calibrate a carb for other fuels.... The O2 sensor reads in a scale called Lambda, and I believe the units are Volts (0 V min - 1 V max).... I don't remember exactly. But you are correct in thinking that if the gauge is reading 14.7:1 and it is calibrated for gasoline, that means Lambda is 1.0, or 1 Volt. So what it is really telling you by saying "14.7" is that Lambda is 1.0. The gauge is doing the conversion for you from Lambda to Gasoline. You have different fuel menus because it will convert from Lambda to a different fuel, just like using a conversion table to use a Gasoline AFR scale to calibrate an AFR of a different type of fuel.
Yeah I'm trying to. It really runs sweet now though from idle to wide open. Maybe should have just tuned it with E10 from the git go, but it's usually garaged over the winter, and straight gasoline stores far better so that's what I try to keep in the tank. Again I don't think it's a huge issue, but it would be nice to know how this stacks up. Near as I can tell from dissecting some of the information online, if the fuel blend is say E10 in the tank, if the idle mixture AFR is adjusted to indicate 14.7, it is really 14.1 as far as the engine is concerned. Innovate in the past had a user forum at their website, though not anymore.
Okay, you're gonna hafta talk to me like I'm 5, something like that, ha ha. One of the reasons I wondered about this, when I drilled out the pvcr's, the WOT mixtures came out a little rich. Not much, but maybe 12.5, and this depends on temperature, it was about 50F when I did my tune. I can of course jet up the mains, or jet down, to adjust the cruise ratio, but the pvcr's size is relatively fixed (unless I drill them out altogether and install inserts) So my thinking was, better a little on the rich size for WOT as it is safer, AND when using E10 or other oxygenated **** they call gasoline these days, it will be right in the zone, if I added half a point to the indicated AFR. Now I'm not so sure. The Innovate didn't have a menu for E10, though it did have a custom setting. I should figure out how to input that, and then wouldn't tie up what few brain cells I have left. Thanks for your advice everyone.
You're not 5 lol - clearly your intellect is capable if you're fooling around with this stuff. I am not sure if the Innovate software is calibrated for straight gasoline, or E10 (10% ethanol), but I would guess straight gasoline. The table above has some irrelevant information, so you'll have to ignore it. All you need is below: x Lambda = y Gasoline = z E10 At stoichiometric ratio, 1.0 Lambda = 14.7 Gasoline = 14.1 E10, therefore you can now make a calculated conversion based off this ratio. 14.1/14.7 = 0.9592 <===== This number is your conversion ratio of E10/gasoline ( or to be formal, 0.9592 : 1 ) So, if you have a reading on you gauge saying your AFR is 13.23, and ***uming your gauge is calibrated for gasoline, your actual AFR using E10 is ( 13.23 * 0.9592 ) = 12.69 , or rounded to 12.7 as the table shows above. The same can be done for other fuels by establishing a ratio between the stoichiometric AFR of the fuel you are using and the fuel your meter is calibrated for. Your meter is reading Lambda and spitting out AFR for gasoline. What the table above allows you to do is translate Lambda into another "language", and by another language, I mean another type of fuel. As an aside (generally speaking, here) - the higher the ethanol content in the fuel, the more oxygen present, the engine will run cooler, and the engine will be more resistant to knock/detonation. GENERALLY. Your numbers don't have to be exact, just close. Get some conservative numbers in your tune, monitor it every once in awhile as a sanity check, and have fun.
As for drilling your PVCR's, it depends on the design of the power valve as to when, and how quickly, that fuel comes in on the curve. The power valve is a normally closed valve, and the valve is opened when engine demand is high. When engine demand is high (under load), engine vacuum is low. Typically a spring holds the power valve on its seat (closed). Once the pressure drops, this valve is lifted off its seat, and fuel begins to flow through the power valve via PVCR's. You are usually better off to play with the power valve spring (to get the fuel in there sooner/later/quicker/slower) before drilling PVCR's. It is not surprising to see your AFR go rich at WOT after drilling PVCR's, because the power valve is wide open. It's no different at that point than putting in larger main jets. You will hear many different theories as to when the power valve needs to do something, but from what I understand, it's best to have it something like this: Idle circuit for idling Pump shot for off the line (can be tailored by volume and duration) Main jets for cruise Power valve is kind of an in-between - you don't want it coming open at idle, and you don't want it to be closed all the way until WFO. There's a happy medium there somewhere. Now, let's say you're happy with your fuel curve all the way until WOT, and possibly due to drilling PVCR's, your WOT AFR is rich. If your AFR's are happy everywhere else, then there's no reason why you couldn't, for example, back off the main jets in the secondaries on a 4bbl by 1 jet size and try again. Which brings a good question, what carburetor are you working with? LOL.
www.innovatemotorsports.com/support/manual/LM2_Manual.pdf The manual does not mention how it calculates AFR, or use with different fuel. maybe the software does? (that you run on your computer to set up the LM2) But if you select the LM2 to display Lambda, instead of AFR, then you should be able to see what's going on. If Lambda is 1, then it's Stoich
I can tell you one thing After using a 4 gas ****yzer for years you will never get a carbureted engine to run properly at 14.1-14.7 especially with distributor ignition . The leaner you go the more spark you need that's why the went to coil on plug ignition or waste spark systems If you can get down in the low 13's you are doing good! Sent from my iPhone using The H.A.M.B. mobile app
Autolite 2100. Stock issue for trucks big and small, with 1.02" venturi. Very responsive with low end torque. What I did, was jet down till the 60 mph or so AFR was in lean best cruise 15.5 to 16.0, no surging or misfire. Smaller jets though, also reduce the WOT fuel ratio. Drilling the pvcr's slightly brings everything back to safe without affecting the new lean cruise ratio. It runs real good now. Saw pretty significant changes based on temperatures too, as running tests from around 40° to 70°F, have it dialed in fairly close to the edge in cruise, nice and rich for power. Went down 5 jet sizes from stock. Will probably have to jet back up 2 or 3 sizes from summer to winter I'd think. Fuel blends change there too.
The Jalopy Journal
