Tuning AFR

[gboone]

The manual says that the AFR should be tuned for what the engine wants. I manually built my AFR table based on the patterns I see in the manual's AFR table. But how do I determine what AFRs my engine wants , for best torque/power, etc., through the rpm and MAP ranges? My VE table is fairly closely dialed into my AFR table using Tuner Studio VE Analyze Live. I've converted from carburetors to EFI and still not making near the torque and power the carburetors made.

[grippo]

The manual should probably say the engine should be tuned to perform the way you want, then the resulting afrs should be put in the afr table and you can use close loop ego to keep the engine performing the way you want. If you want power you need either a dyno or make a pass at wot and datalog and look at the rpm vs times. Make a change in ve or spark table at several selected rpms and loads, then repeat the runs and see what times improved and what didn't.

You can't come up with a magic afr and set fuel according to that - every non-stock engine is different and 11.5 afr may make best power on one car and 13.5 on another.

[Bernard Fife]

Gary,

My view is that you rough tune fuel to avoid harmful conditions like detonation or extreme richness by looking at the plugs, exhaust, and listening to how the engine performs.

Then you fine tune to optimize performance. This can be maximum horsepower, bes throttle response, best fuel efficiency, 'safest' fuel, or all of these (in different areas of the fuel table). To do this, you need to study the spark plugs, and have an objective measure of the target you are tuning for. This means a drag strip, dyno, g-tech pro, a good stop-watch to check 20 to 70 time, or something like that. An experienced driver helps a lot, and will be able to feel even the effect small changes in AFR. People with less experience will have to rely more on objective measures (until they gain enough experience, knowledge and sensitivity).

Always start at low loads and rpms, tune those, then up the rpm and/or load only when those are running right ("what the engine wants"). This does three things:
1 - it hopefully prevent you from breaking engine parts,
2 - it allows you to gain experience in less crtical tuning situations,
3 - it encourages you to use the existing tuned areas to tuning the new areas (i.e. you make smooth changes in the VE/AFR tbale values as rpm and load changes).

There are a number of 'rules of thumb' that can help (12:5 at peak horsepower, 13.1:1 at peak torque for a naturally aspirated engine, etc. But as Al says, these may not be right for your engine (but they may not be a bad starting point for tuning either)).

There is more on this here: http://www.megamanual.com/begintuning.htm#symptoms, but it's not a bad idea to read that whole page as well as this: http://www.megamanual.com/ms2/tune.htm

Lance.

[gboone]

Thanks Al and Lance for the feedback. I think it's time for a dyno tune. I'll post on this forum inquiring a good procedure for dyno tuning.