Finding MBT vs VVT.

[K4Tuning]

Hey all I have a question that maybe a more experienced tuner can help me with. Im getting ready to get back on the dyno and do some more fine tuning with my evo 9. This time around I plan on finding my low/mid range MBT ignition timing. Should this be done with the VVT disabled or does that matter much? I dont want the VVT cam advance to skew my tq numbers if im trying to find MBT. Please let me know if there is an appropriate process thankyou!

[dx4picco]

VVT must be tuned prior to that I would say.

with MAP<100kpa, more VVT advance means more overlap, and more dilution.

More dilution means slower burning mixture and more advance needed for MBT. 

At least this is how I would analyse it.

[K4Tuning]

Thanks for the reply. I do plan on building a more custom vvt map for my car at some point. For now its close to the stock table. It works fine with no issues, I just didnt know if this table should be zeroed out for finding MBT and then turned back on after MBT values are set. Or if it doesnt matter to set MBT values, I guess an added question would be, If I leave VVT working as is and set my MBT, will this change much later when I build my tuned VVT map? I see what you are saying though, Maybe the proper tune process would be as you say tune the VVT map and then find MBT. 

[Vaughan]

Ignition timing is dependent on engine speed and load, engine speed because if the engine is spinning faster you need to start the burn earlier to get peak pressure at the same angle and load because higher density of air/fuel mixture burns faster than lower.

This means that when you tune the VVT to get more air/fuel mixture into the cylinder your ideal ignition timing will need to be more retarded in the same way that running slightly more boost would want more retarded ignition timing.

[K4Tuning]

Thankyou for the response. My strategy for the next time I get on the dyno was to use the steady state function of the dyno to hold 2k, 3k, 4k, 5k rpms, and plug different values into my VVT map to build a “Best Torque” VVT map. Then after that is done, I’ll use the same dyno method do find MBT in vacuum load cells and build the lower part of the ignition map for best torque that way as well. Then after that I’ll blend into the higher boost map that already exists. If there is a more proper way to do this please let me know. Thankyou again for the response!