A/F ratio, how lean is too lean??

[vlado11]

I'm thinking about installing a slip-on exhaust on my k8 suzuki gsx-r1000, that would eliminate the heavy stock cat converter, give me a cleaner look, better sound, and save some weight. The bike has closed-loop FI system, with a narrow band o2 sensor located on the cat converter. The slip-on exhauset does have a bung for the o2 sensor. From the factory, for optimal emissions the air/fuel ratio is set at the stoichiometric 14.7:1. This is little lean to begin with (optimal for performance is said to be between 13.8 and 14.2) and some claim that eliminating the cat would make the bike run even leaner.

So, could anyone speculate how lean is too lean (what a/f ratio) before one should start worrying about engine damage on the long run. I am planning on having the bike dynoed afterward to see the fuel curve, but I do not want to invest in unreliable FI tunning devices such as a power commander, unless I have to.

thanks for any input on this

 

[Eddie]

I think Suzuki tuners would be best able to answer that question. Stoichiometric ratio is ~ 14.7:1 I believe, so I would guess something over 15:5 is getting risky. Ed

 

[1sttruck]

Lean it out until you hole a piston, then richen it back up a tad.

A plug test is cheaper to do :^)

 

[punisher]

Something to consider is that reducing backpressure on a fuel injected engine (even old style non feedback mechical injection)doesn't cause the "leanout" to the same extent you get on a carbed system. Your FI system will richen the mix under load conditions anyway, it doesn't run at stoiciometric all the time. Since you have an O2 sensor providing feedback, I wouldn't worry about it.

 

[sunruh]

too lean is 1% CO. at that point you will start burning parts.

optimum is usually between 6 and 3% CO. depends on the motor.

 

[1sttruck]

So, a typical emissions test can be used to verify final settings ?

 

[sunruh]

i dont know about a typical emissions test. i use a EGA while on a dyno.

 

[PT1]

If you eliminate the o2 sensor you will have issues unless you use a fuel management device like a PCIII to re-map it.Like said before consult a tuner who has experience with your bike.

 

[artificialist]

Sure, if it measures airflow directly with a hot wire or vane airflow sensor. Then the air in is matched with an exact (or really close) amount of fuel.

Now when you get into speed density or alpha-N EFI (Using manifold pressure and/or throttle position exclusively), that is where lean-out is experienced if there is no 02 sensor. When the engine exhales better, it pulls a stronger vacuum. The computer then reads that higher vacuum it assumes the engine not carrying as much of a load, so the level of fuel injected is reduced. In the process, if the spark is electronically controlled, it will be advanced further. That is why reprogramming is sometimes essential to keep the engine from self-destruction.

The other thing that happens with lean AFR is that the spark may not be able to light the air fuel mixture. You will get a misfire.

 

[mechtech2]

Part throttle is OK at 14.7 to one.
But full throttle can and should be richer.
Are you sure the full throttle is adjusted for 14.7, or only the cruise setting?

 

[SD26]

We've always tuned for performance at 12.8 to 13.5:1. There are some options for Suzuki's that don't require you to buy anything. Some dealers have a simple FI box to add a little fueling. Some dyno folks might have a Factory Pro Teka box to do some better tuning. Most dyno guys will try to sell you a Power Commander. Very common piece, but they can be unreliable in some applications.