Yes and no..

The problem with being lean in the open loop portions of the tune, is that the ECM is acting per algorithms based on the way the engine was set up, at the time of the tune... It is not getting real time feedback from the O2 sensors in the open loop. The ECM thinks it is in OEM trim, with an OEM tune... it doesn't know if it's lean or not...

So if you are riding hard and aggressive, you will be in the open loop portions of the tune. If you have gone stage I, adding airflow to the engine, the ECM will NOT be compensating for that extra airflow, like in the closed loop portions of the tune. Without feedback from the O2 sensors, it will change fuel per algorithms based on your OEM air flow... If it's a little lean in OEM trim in the open loop, it will be much leaner in open loop if you add airflow and don't re-tune.

The open loop portion of the tune is the high RPM, high load areas of the tune. Where AFR can be most critical....

The ECM has features to try to protect the engine, like the Twin Cam Ion-Sensing System that senses a spark knock event. It will remove timing (up to 4° I believe) when it senses a knock event... That should help protect the engine, but it's no guarantee. There are other things monitored by the ECM that may also detune the engine in an attempt to save it.. but I am not well versed in them.

If you don't re-tune after a stage I. the question is.. how lean is too lean, and at what point is the engine damaged..??

If you ride conservatively, and don't lug your engine, you probably won't harm you engine for small amount of time you spend in the open loop... If you "ride-it-like-you-stole-it", you could do damage to the engine in the open loop... There are too many variables to say for certain what will, and what won't, cause engine damage..

That's why, with Twin Cams, I always say it's best to retune after even a Stage I

However, if the M8 is richer in the open loop, then that could allow for a bigger cushion to add more air, without causing damage for most riders profiles... I don't have enough info about M8 tunes to know if that's the case, but based on what I've read, it's safer to go Stage I without a re-tune on an M8, than it was for a Twin Cam....

 

I suggest posting these types of questions where in the forum on this site where the experts / professionals live..or just follow the manufacturers requirements as they are professionals too believe it or not

Ignition/Tuner/ECM/Fuel Injection

Need advice on ignition issues? Questions about a tuner? Have questions about a EFI calibration or Fuel Injection? Tips on Engine Diagnostics, how to get codes, and what they mean. Find your answers here.

 

I posted this in another related thread. Here is some data on the subject:

https://www.dkcustomproducts.com/mil...-dk-m8-rpt.htm

 

Old school tuner