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.

[Ed Wright]

Darrel, you have not had problems with Sunoco passing fuel check? Maybe it's better now. I tried that stuff when it first became "the official fuel of NHRA", to prevent hauling fuel in my trailer. Saftey issue. Lost two qualifying runs, at two different races. Bought the fuel from Sunoco at that track. Maybe it's better now.

C11, in my LT1 SS car, runs the same times between 12.8-1 and 13.0-1. Maybe half a MPH faster at 13.2-1 above 7500. I use Speed Density mode, Open Loop.

[Darrel Goheen]

Originally Posted by Ed Wright

Darrel, you have not had problems with Sunoco passing fuel check? Maybe it's better now. I tried that stuff when it first became "the official fuel of NHRA", to prevent hauling fuel in my trailer. Saftey issue. Lost two qualifying runs, at two different races. Bought the fuel from Sunoco at that track. Maybe it's better now.

C11, in my LT1 SS car, runs the same times between 12.8-1 and 13.0-1. Maybe half a MPH faster at 13.2-1 above 7500. I use Speed Density mode, Open Loop.

I have never failed a fuel check with Sunoco or VP. Remember I've only been doing this Stock thing for a couple of years. In the Nova 402 I drove for most of 2 seasons we normally used VP C12 but changed back and forth with Sunoco Supreme 3 times and could see no performance difference. I'm not planning on buying C11 (because of price) even if it means not racing Super Stock unless somehow, magically I obtain some outside funding or if I can find a tune that will qualify in bad air. Last weekend in Topeka it ran a best of 10.58 on C11 in good air and a best of 10.73 (SS/IA index is 10.70) in worse air with 15-20 mph head wind and 75 lbs. heavy. All I care about at this point is being able to run the index. I'll be trying some Supreme next weekend to see if it's closer to C11 in ET. This is in my Firebird LS1 Stock car that I want to run in SS. I've been running Turbo Blue in my Camaro LT1 Stock car. I'll also try Supreme in the Camaro for ET comparison.

I thought you were using closed loop now?

[Ed Wright]

Played with closed loop, saw no need. Once I ran in enough different conditions to get runs in enough different Baro conditions, to get each cell corrected, logs always show correct air/fuel anyway. If it were in Closed Loop, it would not be making any corrections anyway.
The manifold air temp sensor helps consistency a lot. All weekend at Houston recently, it varied exactly one hundredth. First three passes over two days at No Problem Raceway last week, it only varied four thousandths, then it broke a lifter. Did not repeat that close without the manifold air temp.