Fuel injection? Open or Closed loop?

[Darrel Goheen]

Originally Posted by pbp1

At the end of the discussion, all that matters is that you find what A/F reading makes your car run the best no matter where you put the sensor.

How much to you change the target AF at a time when trying to find the best AFR? Thanks.

[cmracing]

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!

[Darrel Goheen]

Thanks for the info. I really appreciate it. I don't know if my engines are considered low or high hp or somewhere between. They are both Stock Eliminator engines. One is a LT1 and one is LS1. I'm assuming they are considered low hp. I really don't even know where to start on WOT AFR. I have them both on 12.7 after about 6000 rpm and about 12.1 on launch (3500) and then take fuel away to 12.7. The O2 sensors on both cars are in a header tube.

[cmracing]

You're a 'tweener, which is just fine.

They can probably tolerate 12.1 A/F at the launch, but play-around. See what happens as it approaches 12.5 to 12.8 at the hit. If the 60's don't like it, go the other way.

I imagine you run C11. You can normally go up to 13.0 A/F with that fuel without hurting power. Heck, I have seen up to 14.0 A/F and not hurt the engine, but it did slow down. Again, find out what it likes. Some engines like a flat fuel curve from start to finish, others like to change A/F though the pass. With EFI we are free to experiment with just a few keystrokes!

I have found the higher the octane, the leaner it likes. I have not used oxygenated fuels so I can't speak for tuning them.

[Darrel Goheen]

Thanks. I plan to run Sunoco Turbo Blue. That's what I've been running in the Camaro LT1. I'm still using C-11 in the LS1 but plan on switching to Turbo Blue at the next race.

[cmracing]

How does the LT1 compare to the LS1? The LS engines have a terrific head, but have they been killed with HP? Do they hold-up without oil pressure issues? I have seen several munch cam bearings for no reason..... And these were just 500-600 hp street engines spinning less than 7000.

[Darrel Goheen]

Sorry to say, but I don't know a lot about either engine.