Definative A/F - CO2 - and Lambda testing thread
 

Okay.... a lot of reading, but not a lot of understanding :)

I have managed to aquire an exhaust gas tester that does CO2, O2, Lambda and A/F measurements. The sensor is inserted up the (in my case single) exhaust pipe. I run headers that do not currently have provision for an O2 sensor. The unit is able to be fitted to the car and used in "mobile" mode.

I understand that I'm looking for about 14.7 for A/F readings, but is this at idle, under load, high revs? Currently I have everything looking quite good at idle, but at WOT the mix goes very rich.

I'd love some good practicle advice on the figures I should be looking at throughout the rev range

Engine is my (very sweet :) ) 2.7RS rep on webers with PMO recommended jet and veturi setup.

Thanks

C'mon... I know there are some Gurus out there just busting to talk tech with me!!

I don't have experience with the gas readings. I could look up some book info if nobody comes forth with hard experience though.

under acceleration the circuit dumps a lot of fuel cooling the combustion temps. Cool combustion is inefficent combustion, but that's life in the carb world. What's important is that it accelerates the way you want. I'm presently involved in the acceleration myself.

Do you have a problem with your carb or ignition settings?

Hi Ron. It seems to be running great. I have a mild transition issue from the idles to mains but I'm fairly sure that is just a case of coming up from 55 to 60. There is a mild/occassional pop on deceleration. I guess I'm looking to make sense of the readings I get from the analyser.

Greetings. great is a wonderful thing with nice carbs. gotta love it.

I'd probably start a log of a bunch of different settings in an orderly way and record the meter readings for each setting. The engine should really warmed up about 8-10miles of highway driving. I'd wait it out till that point for the hard info. I wouldn't even be concerned about the main circuit for now. I'd be concerned with the various idle jet settings and your acceleration circuit.. and at what rpm's the secondaries come on.

Maybe someone like Sherwood, JW, Quiet Boom, Grady, etc will jump in and give and be able to offer some advise on this. I'll wait this thread out till tonight/ 16hrs to offer my approach.

meanwhile.. what distributor are you using? vacuum retard plugged in? initial&total timing? Spark Plugs #'s? current idle mix settings? Are they all the same settings? Have you tried different settings? what happened at different settings? Are you doing all this yourself? Have you had performance carbs in the past? if so did you operate on them yourself? How is a cold start? at what ambiant temps? What venturi size? What ignition? What are you using the car for? What design is the fuel feed?

it's a 911 carb eating MFI world imo.

Ha! :p

Ditto HA! :D (edit) Tom Wilkinson has cars that run each system. I'm going to send him a link to this thread. I'd welcome either of his cars in my garage anytime...

At idle you want to around 14.7, mayber slightly richer depending on if you have to deal with emissions testing.
At part throttle cruise you want to be around 14.7, maybe even a little leaner.
At full throttle you want ot be rich. Around 13 to one is max torque, 12.5 to one is better if you have problems with pinging or are running high boost levels.

John,

I agree with Ronin, lets establish a base-line first. Be very patient as it will take some time and resist the temptation to jump into changes. Part of what you are doing here is finding the consistency of measurement of your new tool. If possible, compare it to other’s exhaust analyzers. Note both the absolute numbers and the consistency.

For there to be a meaningful interchange you will need to document and post everything. There isn’t a seemingly insignificant detail that isn’t potentially very important.

The first things to do are to document several compression and cylinder leak tests interspersed with some spirited highway driving. Next will be to make you (us) an accurate distributor advance document. Additionally you want to make absolutely sure of the jets, venturi, etc. in the carbs. For this exercise, actually measure the jets; don’t rely on the stamped numbers.

You want to make sure there isn’t any possibility of an ignition issue. Even the slightest bad component can lead you (us) down the wrong path.

Best,
Grady


BTW, I’m really sorry we didn’t connect at Ventura. It’s a pain when the brain wants to do one thing and the bod says no.
G.

The relationship between air fuel ratio and engine performance is well understood, and, for the hard-core engineer, a copy of "The internal combustion engine in theory and practice" by Taylor is an overload of fabulous data. Slightly less geeky is "internal combustion engines" by Haywood.

Basically, 14.7 to 1 is the "chemically correct" air fuel ratio for gasoline that exactly consumes all of the oxygen in the air when burning the fuel. It matters for emissions, but otherwise, it's just a benchmark.

Assuming you're not knock limited, 12.5 to 1 is max power, full stop, no questions asked.

On boosted or knock limited engines, you can increase power by increasing boost and adding fuel to prevent knock. This works up to about 10 to 1 air fuel ratio.

At idle, it's all about idle quality, and somewhere between 14.7 to 1 and 12.5 to 1 is optimal.

In cruise, it's all about economy and, 16 or 17 to one is best, but you need to use lots of vacuum spark advance to prevent misfire. Leaner is better as long as you get smooth running.

For transients, tipping into the gas, etc. You want to stay above 14.7 and below 12.5 to one for best response. This is accelerator pump territory, and it's all about tuning the flat spots.

So, for a naturally aspirated engine, you'd like full throttle runs to peg at 12.5 to 1 across the whole RPM band. And, you can try tip-in from 1000 rpm, 2000 rpm, etc. slow and fast tip in and make sure the guage doesn't go lean of 14.7 or rich of 12.5 (on the rich end of that range). Cruise on the expressway, make sure you're in the 15 + range.

Also, the cylinders run hottest slightly rich of 14.7 to one, so stay out of that range for cruise.

Great stuff guys, thank you. I'm currently "out bush" for the week with work, but look forward to playing with the car this weekend, I'll post a complete list of settings etc...