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cmracing · 03-22-2017, 12:07 PM

Lower compression/horse power engines have a wider A/F range that they will operate in than high compression/horse power engines do.

You may find that the low power combo will tolerate an A/F swing of .6 total (.3 A/F rich or lean from mean) and be just fine, may not even show on the timeslip.

A high power combo may barf if it is run too rich (and that can be .2 A/F from mean). I'm not talking down a little bit in power, I am talking about it being flatter than flat and not moving in the first 60/330 ft.......

So, to be safe, vary it .2 A/F up or down and keep track of conditions. Learn what your combo likes.

I don't travel much so I make very few changes during the season. Unless I go to Numidia which has a much higher altitude than the other tracks I race at, I really don't touch the tune. Rarely do we get huge swings in temp/humidity around here, but it does happen.

I lock down the wide open throttle correction at 2%. After a pass I look at what it tried to correct. If I see it pinned at +2% or -2% I may make a slight change. Usually it will show nothing on the timeslip, but I am after consistency which I have no problem with using EFI.

I don't believe in the "fast tune" or "killer tune". I give the engine what it wants each and every pass. Every 500-600 passes it gets pulled and freshened. Bearings and rings/pistons tell me if they are happy and after 20 years of this they (and my wallet) have always been happy!

03-22-2017, 12:07 PM	#92
cmracing Member Join Date: Aug 2016 Posts: 173 Likes: 113 Liked 62 Times in 29 Posts	Re: Fuel injection? Open or Closed loop? Lower compression/horse power engines have a wider A/F range that they will operate in than high compression/horse power engines do. You may find that the low power combo will tolerate an A/F swing of .6 total (.3 A/F rich or lean from mean) and be just fine, may not even show on the timeslip. A high power combo may barf if it is run too rich (and that can be .2 A/F from mean). I'm not talking down a little bit in power, I am talking about it being flatter than flat and not moving in the first 60/330 ft....... So, to be safe, vary it .2 A/F up or down and keep track of conditions. Learn what your combo likes. I don't travel much so I make very few changes during the season. Unless I go to Numidia which has a much higher altitude than the other tracks I race at, I really don't touch the tune. Rarely do we get huge swings in temp/humidity around here, but it does happen. I lock down the wide open throttle correction at 2%. After a pass I look at what it tried to correct. If I see it pinned at +2% or -2% I may make a slight change. Usually it will show nothing on the timeslip, but I am after consistency which I have no problem with using EFI. I don't believe in the "fast tune" or "killer tune". I give the engine what it wants each and every pass. Every 500-600 passes it gets pulled and freshened. Bearings and rings/pistons tell me if they are happy and after 20 years of this they (and my wallet) have always been happy!