Air Fuel Ratio chart

[David]

Thought some of you guys could use this:




From the Motec site:

peak power at Lambda between 0.84 and 0.90 (non-turbo obviously)
best economy at Lambda equal to 1.05
optimal emissions at Lambda slightly lower than 1

[jcc911]

So with a low boost aplication (on a 3.0 SC) I would want the ration to be between 12.5 and 13.2? Is this on boost or through out the RPM range?

[David]

That's just on boost. Since it's air-cooled, I'd go 11.8 at full boost to be safe.

[911nut]

We all run rich because we assume that air flow is not equal to all cylinders.
If we were building race engines that had to develop max power with the highest possible economy, we'd flow the intake and heads until everything was near equal and run an afr of 12 - 12.5 because that's where max torque is made, regardless of whether the engine is turbocharged or not.

[Benny771]

Originally Posted by 125shifter

That's just on boost. Since it's air-cooled, I'd go 11.8 at full boost to be safe.

Whats the "easiest" way to check this?

Some type of analyzer i can buy?

[David]

The easiest is to take it to a tuner shop and have them put it on a dyno with a lambda sensor in the exhaust pipe.

There are stand alone lambda sensors you can install. I think they're anywhere from $400 to $2000.

[Benny771]

Originally Posted by 125shifter

The easiest is to take it to a tuner shop and have them put it on a dyno with a lambda sensor in the exhaust pipe.

There are stand alone lambda sensors you can install. I think they're anywhere from $400 to $2000.

What about those tail pipe sniffer thingies?

[HelmetHead]

Why Yes Thank You....I do need this! Lambda sensor came in today!

[911st]

Here is a Co to AFR chart: The MG & MGB Experience: Library: CO% to Air Fuel Ratio (AFR) Table


I believe max TQ is at about 13/1 to 13.2/1 for a normally aspirated 911 motor. I have seen a turbo at 13/1 but that takes a lot of heat management and race fuel.

Many tuned performance turbos run in the 12.2/1 range that have more accurate fueling and adaptive systems to protect the motor.

Many turbo cars that come from the factory like WRX's will often run in the mid 10's in stock form on boost. My guess is to protect the motor from detonation.

I believe we tend to want to run in the mid 11's at TQ peak where risk of detonation is highest.

Not an exert on this, just what I believe so far.

[911st]

Using the Co chart, setting idle CO at 3.5% gets us a 13.2 AFR and should achieve the best pre-boost performance. Stock Co gets us around a 14/1 AFR which is better for idle and cruse AFR.

Unfortunately the 3.3 930's do not have acceleration enrichment,just boost enrichment, so it comes to a decision between performance or efficient cruse MPG. The 3.0 Turbos did have acceleration enrichment with loss of manifold vacuum.

Getting a more ideal pre boost AFR and ignition advance can noticeably improve off idle performance.

[David]

Originally Posted by HelmetHead

Why Yes Thank You....I do need this! Lambda sensor came in today!

Tuning drive tomorrow evening?

[HelmetHead]

Perhaps later in the evening...I got the Kiddo solo tomorrow.

[Richard930]

Benny771 - where are you located? I've got an Innovate LM-2 AFR meter on order and will be willing to 'consult' with it, for a small fee of course!

[dicklague]

check out the Daytona Sensors Wego IV. Pelican now sells them. I have one and it is a great AFR unit with data logging.