that air fuel ratio is dangerously lean to most engines... a NA motor should see 13.0 at WOT... a turbo engine should see at least 12.5 or richer at WOT... basically the higher the EGTs the engine produces, the richer the mixture has to be to quench the combustion temperatures... golden rule, above 1,700 degrees... you melting the internals.

here is the worse part, the leaner mixture is actually producing more power than the 12.5 they suggested would... but it is not safe as the EGT (exhaust gas temperature) values climb very high at WOT load... the leaner the mixture the hotter the flame front and more violent the explosion, so long as the engine can hold this without puking its guts out, more power will be made... great thing is, we know this engine can hold alot more power, bad thing is, the aluminum pistons will expand more than they where designed to with elevated combustion chamber temps possibly creating some big problems.

the ECU has a long term and short term fuel adaptive. short term is adjusted when you drive around at non WOT condition (regular driving) based on 02 readings (most ECU's will allow a 25% trim + or - ). then when you finish your driving the short term adaptives for the different RPMs you drove at are stored in the long term adaptive memory. not having the catalysts in place means the upstream o2 sensor (fuel trim for optimal fuel mileage is recorded by this) is seeing the same value as the downstream o2 sensor (fuel trim for optimal catalyst efficiency is recorded by this). this gets sent back to the ECU as a failing catalyst at which point the ECU will elevate the EGT temperatures to attempt to bring the catalyst temperatures up so that it may do its job of burning off impurities... how does it do this ? by leaning out the mixture = raised EGTs = hotter cat...

now, although the adaptives are ONLY adjusted during non WOT conditions... they are applied to WOT conditions... so there is where i think you are getting your leaner than healthy mixture at WOT... the system is trying to raise the efficiency of the catalyst (which is not there but the system does not know this).

i've fought stock ECU programming for years and its not pretty but very doable...

use a Apexi Super AFC to counter act the programming, you can adjust up to 30 percent trim + or - with it... setting the hi/lo throttle switch off to 90% TPS signal before it goes between the hi/lo map on the AFC, i have been able to counter act the stock ECUs attempts to trim the fuel to raise the EGTs for the catalysts sake... i do this by connecting a OBD2 meter to the car and watching the short term adaptive at different RPMs, and i just counter act the ECUs cuts with the AFCs lo throttle map 1% by 1% until the stock ECU runs out of room to adjust... then i use the AFCs hi throttle map to tune the car to a perfect air fuel ratio which does not need to be monitored Vs the fuel trim of the stock ECU as the hi map is only active at WOT where the stock ECU does not adjust based on o2 feedback...

done right the results are spectacular... i was able to tune my brothers Eagle Talon TSI (front wheel drive + automatic !) after we put a large turbo on it and oversized injectors to run perfect at idle with the stock ECU (larger injectors with stock ECU = way rich all over) and still be able to pull off a 13.2 in the 1/4 on drag radials...

one thing to be careful with... you are messing with the ignition timing as well when making adjustments with a SAFC as it messes with the signal the MAF sees which is used in calculation of the ignition table as well...

i have also done research on using a Greddy Emanage Ultimate and Greddy Emanage Basic on the cross.. the Ultimate is out as it is very car specific according to greddy engineers but they are confident the basic will work. i am confident the basic unit can trim fuel and add it too just like the AFC does but i do not know if the ignition control part of the greddy unit will work on the cross even though the wiring they describe for v6 with individual firing is what the crossy uses (coil on plug system)...