I'm trying to educate myself and learn more about my FD. So far, others have tuned it, but I'd like to learn more about it myself. At the moment, my A/F ratio is at about 11 for most of my curve. I know this robs me of some power, but how lean can I go without killing my engine?

 

I hear venting the stock BOV will help balance the a/f ratio..........

 

11.5 is the leanest i would go

in anycase, venting the bov probally wont do anything seeing as we have map and not maf sensors.

 

Venting the stock BOV wont help since it is not setup as a diverter valve (such as DSM's). 11:5-12:1 is about where you want your air fuel ratio at. Running your car leaner isn't going to increase your power, its just going to hurt, more fuel is better, too much fuel is bad. What kind of setup are you running anyways that others have to tune it?

 

Venting the stock BOV wont help since it is not setup as a diverter valve (such as DSM's). 11:5-12:1 is about where you want your air fuel ratio at. Running your car leaner isn't going to increase your power, its just going to hurt, more fuel is better, too much fuel is bad. What kind of setup are you running anyways that others have to tune it? If it was professionally dyno tuned, your car should be just where it should be. I dont understand how someone else could tune your car otherwise unless your using other peoples fuel maps or something, which is not a good way to go.

 

Rotaries don't make a ton of power by leaning them out much further than that. My buddy Eric's car only picked up 7whp going from 11:1 to 12.5:1. It's not worth it. If you're at 11:1 that's fine, keep it there.

 

Everyone's car is different. Not too sure what was on your buddy's car, but only a 7 RWHP when going leaner (over 11.1 to 12.5) is poor. May have been some other issues.

My experience is good power is available leaning from 11.1 to 11.6 / 11.8. That is my limit, but I feel confident about my set up.

YMMV. Use caution, the leaner you run, the less tolerance you have for an anomaly, i.e., overboost, timing error, etc.

 

I dont think we have timing problems....

 

Go to the ECU section and research.

 

Well, if a trailing spark plug fires before a leading spark plug, then it's not really the best thing for your motor.

Don't believe me? Go swap your plug wires and see how many miles you can drive .

 

Even though I dont know exactly what would happen if someone were to do that (I can take a wild guess though), I dont think we should say that. Hopefully no one is gullible enough to try it just to see what happens.

**ludeowner goes to swap his leading and trailing plug wires**

 

Within a fairly short period of time, your plugs will fire over (or near enough to) the apex seals as it crosses the plugs......upon motor teardown you will most likely find your apex seal springs flat. No compression is a bad thing.

That's why when you're doing your own plugs, always do one wire at a time. The leading plugs fire off of the same coil, so swap those bad boys to your heart's content.....

 

Actually I just checked and my A/F is at 12. Is that too lean?

 

FYI - I'm measuring A/F at the tailpipe and not the downpipe...if that helps any.

 

So are we talkin' 12.0 the entire time you're on boost? Also, how much boost? It's a little borderline.....on the dyno you'd prolly be showing 11.5s, which is fine. You should be ok, but a little more fuel would be a good thing.

 

What's a stock midpipe? Cat converter? If you are measuring at the tailpipe and have the stock converter in place, there will be a small impact on the accuracy of the A/F (since you are injecting air into the exhaust).

 

I'm at 1 bar, pushing 360rwhp. 14 A/F @4100 rpm, 13 A/F @5000 rpm, 12.5 A/F @5500 rpm, 11.9 A/F @6000-7500 rpm.

 

That actually sounds like a pretty decent tune. Tho I'm too much of a ***** to go that lean down low

 

Thats a kaboom tune. You're way lean at peak torque. You could probably get away going the other way (ie 11.0-11.5 through peak torque, then up to 12.0 in the high revs)

 

Homie - when you say "stock midpipe" what do you mean? Are you meaning catalytic converter?

 

No cat ! HKS downpipe and I just put on a Pettit midpipe w/resonator. The cats are all out now baby!

 

Go with what Marshall said. You need to richen up the area on the map that corresponds with your dyno plots peak torque. If its at 5000 rpms, then that is where you need to be 11.4 or richer depending on your car. Assuming your running twins sequentially, 5000 is around the peak torque and your pretty damn lean (13 to 1) at that point. Richen that thing up to to 5000 rpms and you can raper it off to redline with maybe 11.8 to 11.6 at that point.

Right now your playing with a time bomb and need to tell the "tuner" to add some fuel or its rebuild time.

Tim

 

One other point......measuring from the tailpipe is fine, but make sure that you don't have an exhaust leak. This can cause you to show a richer reading than you're actually getting from your motor......

 

I am not sure how a leak will make you read richer or leaner (leaner was said before). Air will not leak in, exhaust gas will leak out, but if it is going to read richer the assumption would have to be that just the O2 is leaking out? I don't see how that can happen.

Maybe I am not seeing/understanding something...

 

When you're tuning on a dyno, typically they provide a wideband for you. This is what they use to determine your Air/Fuel ratio. When you have an exhaust leak, some of the exhaust can leak out before it reaches the wideband. The wideband will see less exhaust coming out. Since it can only give a reading based on what it can see, the mixture it sees could be leaner/richer than things actually are. When you're tuning based off of an inaccurate reading bad things could happen.