Tuners Please Step In. Question on AFR

[SSGT_B]

Ive been tuning Corvettes since 05. Built and tuned my own twin turbo Vette. Im confused at some posts Ive been reading lately. So here gos my stupid question of the year.

Now that Im able to actually see the AFR of my bike while riding I can verify that its pig rich. At least in the car world it is. Is there and difference in running afr for a bike? I ask because a few post I have read people are saying that their bikes were changing afr due to density altitude. here is the quote

" The Air Fuel Ratio on a normally aspirated Busa changed accordingly from 13.0 - 13.2 all the way up to 13.6. That's overly fat to dangerously lean and on the edge of detonation"

Since when has anything under 1 lambda , or 14.7 AFR fat?? Do bikes run that different from cars that they need to be this rich? I have always noticed that I smell bad of fuel after a ride and now I know why but the question remains. Nothing will replace a dyne tune but I have the ability to log, chart, and adjust to a degree my AFR. So what is the deal for bikes? my cruising AFR yesterday was better 12.5-13.5 AFR. Thats too rich to me for non loaded cruising. Thanks

 

[RedBull]

 

[Mythos]

Now that Im able to actually see the AFR of my bike while riding I can verify that its pig rich. At least in the car world it is. Is there and difference in running afr for a bike?

Yes. 14.7 is the ideal AFR for cars but that is quite lean for running a bike. It might be ok for cruising the highway but I would not go that lean on the top end or even midrange.

" The Air Fuel Ratio on a normally aspirated Busa changed accordingly from 13.0 - 13.2 all the way up to 13.6. That's overly fat to dangerously lean and on the edge of detonation"

I only have experience tuning my Gen1 ZX-14 but 13s are not "pig rich." That's about where you want to be if you want hp without getting too risky about running lean. 12.00 is rich. 14 is lean although I have heard of people using that AFR for their cruising zone. High rpm, that lean could result in burning valves or something. I'm not sure what the ideal AFR us for the busa but Gen1 ZX-14 is 12.5~13.

Also, my 14 is constantly wandering back and forth within about a half an AFR number with AutoTune and this is running on level ground. The only time the AFR is stable is after I have been cruising for a couple seconds and AutoTune has the time to narrow down the A/f mixture. If racing, turn AutoTune off. It's great for tuning runs or cruising but it's too slow to keep the AFR perfect in closed loop. Tune open loop and then shut AutoTune off for optimum results. I've never tried that myself. I think the AFR is still going to wander because the ECU will adjust fueling for various reasons. Stock equipment for correcting AFR on cars is a lot faster than what bikes have. Anyway---what I'm saying is I think the AFR is going bounce around a half AFR no matter what you do.

I like my map with multiple target AFRs for various TPs and rpm zones a tiny bit better than my straight 13 AFR map. I have not learned all the secrets for choosing the best AFR for specific zones. Rich for best torque, lean for best hp is all I have been told....and quite lean (AFR 14) for highway cruise zone is acceptable.

my cruising AFR yesterday was better 12.5-13.5 AFR. Thats too rich to me for non loaded cruising.

You can go leaner for cruising. As mentioned before, I would not go leaner than 14. It might be ok....I have heard of a guy who tunes very lean for cruising. I can't remember what number he shoots for. Personally, I would not want to experiment with mixtures leaner than 14 without getting expert advice.

If you'r using AutoTune, here's the whole story. There is some info that i believe is pretty specific to the ZX-14 but I plan to follow the same general procedure for my busa :

http://zx14ninjaforum.com/messages.cfm?threadid=82EE3378-978F-4244-17A47B554179390E

 

[sixpack577]

Powehouse??
Boosted Cycles??
What's the verdict?

 

[SSGT_B]

Thanks for the information. Like I said all my tuning has been turbo cars or big cam cars. I mostly tuned for e85 + methanol but have tuned gas too. Bike tuning is new to me and I don’t want to goof it up and eat a motor before I am able to get it done right. I’m tat guy who can’t leave stuff alone lol

 

[POWERHOUSE]

The norm for any motorcycle is 13.2. You can lean on that number for steady state or cruise situations, generally going 13.5 - 13.7. Over 14 is starting to go too lean, you will lose power, but is fine for an unloaded engine - for example, a bike that is idling. Certain models have exceptions, like Kawasakis, which tend to make the most power around 12.8 - 13.0, a little richer than most other bikes. 15:1 is too lean, getting close to a lean misfire, which might occur at 16:1. The most power on a normally aspirated bike is usually attained between 13.2 - 13.5; again, there are exceptions to this. What is nice about a custom dyno tune is the ability of the tuner to target multiple afrs within the same fuel map. Someone that wants the best highway fuel economy can have that and also the most power by targeting and tuning certain areas differently.

 

[SSGT_B]

Thank you Frank. Think I’ll stop tinkering and leave my tuning to only cars. Hopefully I can get the bike up your way this summer. I’m sure you can work magic on it. Ultimately I am looking for the highway mileage without loosing much power, but misty importantly, a smooth transition across the board. Thanks again for the clarification.

 

[RansomT]

The differences are actually 2 fold. Modern sport bikes have a way more efficient head that cars and bikes have a difference in cam timing than cars because of the much higher RPM they make peak power. The cam differences show up as overlap and creates a indicted false rich reading. So a bike a low load and idle may show a 13.5:1, in reality it's closer to 14.5:1. The head comes into play with higher RPMS and load, a pump gas tune of 13.1-13.2:1 would cause havoc on a lot of sports cars, but is just right on a sport bike.

 

[mjl3truck]

AFRs are like grandma’s undies, depends.

 

[BusaWhipped]

I have my 6th gear highway cruising throttle position/rpm tuned to 14.5:1. Anything else non boost is at 13.8. anything that gets into boost is 11.5.