I have a s5 n/a with a Apex'i S-AFC II that I need to get tuned and was wanting to know what is the ideal AFR that I should aim for. Should I try to make the AFR flat across all the rpms or should it have different AFR at different rpms?

~George

 

Well i don't know too much about N/a AFR's but EGT's you want to be around 760C at WOT

I think for an N/a you don't want to go higher than 13'ish AFR

 

Hmm.. Interesting question.

The obvious answer for most power is, lean as you can get it without pinging. I am not terribly sure how bad pre-ignition is for an N/A, but my guess is, its not half as damaging as it is for a boosted application.

 

I will usually misfire well before I detonate on my n/a.

Tune for best power if you are on a dyno. If you have a wideband and no dyno, tune for high 12's to 13:1

 

Thanks for the help guys, so you think high 12's to 13:1 would be the best for all around performance in an n/a.

I not real sure what 1987RX7guy was talking with EGT's and the 760C; would someone fill me in please?

 

EGT is Exhaust Gas Temprature.

Its another way to measure mixtures.. Lean mixtures = higher EGTs..

 

I tune for 13.2 on WOT and 14.7 on cruise

And running "just lean enough not to ping" isnt a problem on an N/A really. As previously stated, you will missfire an N/A before you ping, and you're not making really fantastic power there either.

 

right.

base run, then go rich, then go leaner, see where you make the best power. stick it there. not necesarily a specific afr. my buddy went to a dyno "tuner" shop here, and the RETARDS tune only to AFR. they do some runs and Ted tells them to go richer up high, it picks up a few hp. well that doesn't matter they tune to afr. they stick it back to 11.5:1 (their forced induction general purpose afr) and that's it. btw, their afr tuning actually shaved like 6-10lbs of torque off of the low end 3-5k rpm range. bunch of idiots...

 

Oh yeh, disconnect your airpump line while tuning, and find another way to open your aux ports. That split air getting into your exhaustr will throw the wideband WAYYY off :O

 

In my findings, I get peak acceleration with 13.6-13.8 AFR's at peak torque, dropping to 13.4-13.6 AFR's at peak power.

The richer/leaner fuelings depends on the level of porting, and I have different base AFR values for BP/PP engines.

I tune for ~15.5-~15.7 AFR's under cruise, just on the edge of bucking, to maximise fuel economy and keep carbon production to a minimum.

 

See, I tried running at the edge of bucking at cruise, and my fuel economy went *down* - I've found that slightly lean of stoich seems to be getting me the best range.

-=Russ=-

 

does timing affect your afr at all with a stock ecu? i just advanced mine 30* and it has much more power up top. its an n/a

 

for the 15.5-15.7 AFR's, was there air from the air-pump going into your exhaust ports at that time, or did you have it disconnected? I'm asking because if there WAS air going in there, your actual AFR was more like 13.5-13.7.... (according to some testing I did with the wideband, and disconnecting and reconnecting the air pump, I'm sure you knew this already) and you didn't specify one way or the other

Another question, at low load and high revs, what afr's do you generally tune for? Meaning I'm at 5000-6000 rpms, and just cracking the throttle open enough to maintain those revs.

 

Give me a little credit here, of course I knew this.
I always disconnect the air pump if tuning a stock-ish car.

If its a motor I've built, you can bet that the exhaust sleeves have had the fresh air feed holes welded shut with a plug of stainless and then ground smooth again, an aluminum plug pressed into the exhaust port feed, and then four aluminum plugs pressed into the holes below the exhaust ports.



Depends on the motor. Little below stoich, usually.

 

I don't have the air pump line going to the exhaust, it just blows in the engine bay and my aux ports work fine.

 

OK, well I'm new here, didn't know you from anyone else. I know better now


OK, I'll have to try that, right now we're tuning for stoich there, and we get a little surging whenever the computer over-compensates and goes a little leaner... (haven't tuned the map, so letting the computer run closed-loop to get some datapoints with the wideband). I guess I'll drop it to like 14.4 or 14.5 at those points, and see what happens.... I'm running even leaner at the very bottom of the map (lowest load) and low revs (below 2800) and that seems ok (15.2:1).