kkarim

iTrader: (2)

I know there a lot of topics on this subject already, but i still haven't found a REAL answer.... Most of the answers I can find are concerning 91 California fuel.

Over here in Lebanon, we have 98 RON fuel (i think it's equivalent to the 93 US).

I've been told that my AFRs should be 13ish during spool, then 11.0-12.0 and LEANING OUT a bit (12.3-12.4) towards the redline.

Can I get some more hints please? All of the guides I found on evoM use 91 California fuel..

nothere

iTrader: (23)

generally people will say 12,13 at spoolup and 11.5 the rest of the way.
some others will say 11. all the way
you can do the afr you asked about if you have adequate cylinder cooling. meth or water, and then maybe even a bit leaner.


afr are as many as there are tuners, try the middle of the road and log, then go from there. iow give 11.5 a shot and see if it needs more fuel or not. of course you then can reduce timing to try and carry a leaner afr too. either rely on a tuner or expect to do a lot of trial and error.

justboosted02

iTrader: (31)

leaning out afr's will give you a little bit of power when they are leaned out but the power difference between say 11:1 and 12:1 wont be that different. timing makes a much bigger difference.

I shoot for 11:1 during boost spike then lean it out to 11.5:1 till 7000rpm then 11:1 to 8000rpm

BTW an afr of 12.3:1 at WOT is considered very aggressive and IMHO you are playing with fire if you get a bad tank of gas

kkarim

iTrader: (2)

Ok. A friend of mine (amateur tuner) was telling me that my afr curve should lean out by about .5 by the redline due to the reduced VE of the engine at high RPM.

Can anyone help me out here? Is he making sense?

Jack_of_Trades

iTrader: (17)

Most guys will richen up the very top end to minimize knock occurances because even a small amount of knock as such high RPM's can cause greater damage. Most tuning shops will do this for additional insurance against engine failures. Ideally, your fuel will achieve optimum power at 12.5:1 so thats your goal...an optomistic one though. You want to tune for as close to this as possible while still gaining power and avoiding knock. 11.5:1 is a more realistic target because you are using the additional fuel as a cooling agent for lower cylinder temps as well as a cushion for irregularities in the fuel mixture. I personally strive for 12.5-13:1 at peak load, 11.5-12:1 thoughout the powerband and tapering to around 11.2-11.5:1 after 6500-7000rpm 'til redline.

There is a point where more aggresive timing (or higher boost) and less fuel help but the aggresive timing/higher boost usually yields higher gains, thus the rich mixtures by most people. A more efficient/cooler air intake charge and a closer tune to 12.5:1 would yield more consistant results IMHO.

Chamama

Is it helpful in any way to richen the AFR at boost spike? I have seen maps where the spool up is at 12:1 and then at boost spike 11:1, and then leaned out to 11.5:1 tapering to 11:1 by redline.

justboosted02

iTrader: (31)

i like to keep it rich at boost spike because boost spike is notoriously uncontrollable and i like the extra safety margin. depending on weather my boost spike can vary by as much as +- 1.5 psi

Jack_of_Trades

iTrader: (17)

A lot of guys will go as lean as they can get away with at the boost spike area since its usually the peak torque area as well so they try to get the torque numbers nice and high. Like justboosted02 said, its a tricky area on some cars so adding a bit more fuel can aid in knock-free repeatability from run to run. Once a car knocks at peak torque, it can linger 'til redline which just KILLS your timing curve.

SLO-EVO

iTrader: (52)

mine is ~ 12.5 during spool up and gradually drops to ~11.5 as rpms climb/peak... as said earlier, you are going to have a big range of AFR #'s cuz everyone has an opinion on where your afr should be..