boosted951

I have a copy of my dyno sheet that the previous owner gave me. I have been doing some research on the A/F ratios and wanted to see how far off mine was. I do have an Apexi S-AFC II and the previous owner said he has it set where at 4000 rpm...he has it set to a maximum 50% to run rich. He said on the dyno sheet that it was running a little lean on the top end and that is why he had it running rich. I realize I do need larger fuel injectors. Maybe a FPR etc... Any advice on how to tune the afc without detonating my engine? I have not attemted to adjust the AFC just to play it safe. Any suggetstions or opinions would be appreciated.. I am running 16psi of boost with the mods listed below. Am I hurting the engine going lean at the top end? Should I not rev that high? Anyone up for a Dyno day here in Atlanta sometime soon? I realize that is the best way to tune the car...on a Dyno and with a wideband.... I do have a A/F guage, installed, but it is not hooked up.... P.S. I also have this posted on the 951 turbo forum....

C2 Turbo

Well i'll try to give you some insight before someone more knowledgable person chips in.Before you start interpretting the A/F ratios,you need to know what the trem " Lean " and " Rich" means.
Rich: Enough fuel but little air and thus is safe for the engine.
Lean:Enough air but less fuel and thus dangerous for an engine.
Ideally tuners like to keep the A/F ratio right around 12:1 esp up top and in you case from 3500 rpm-4500 rpm you get too rich and then as you go further up on rpm's the car gets quite a bit leaner which doesn't look too good.Any time you are running rich you lose power so by leaning out the A/F right around 3.5k-4.5K RPM you surely will gain some extra ponies but at the same time i definately will richen the car a bit esp up top.
Hope it helps.

eman930

I have heard for performance reasons its always better to run just a little rich, more power

adrial

As the boost is ramping up, it seems you want to run it a little leaner than 12, 12.5:1 to get the turbo spooled up faster (hotter exhaust gas-->better for turbo spool)... Beyond spoolup, 12, 12.5:1 is a good area to shoot for.

10:1 is way too rich.

A930Rocket

Actually, a little lean gives more power, but too lean and no power.

boosted951

thanks guys

Willard Bridgham 3

The problem with changing the injectors on these cars is that they are 4.5 ohm and nobody makes them but bosch. If you change the injectors with the stock DME/KLR, you'll have to either add some resistance or reduce it. Engine managment systems will let you choose injector resistance

If you want more fuel, change the fuel pump to a higher volume pump and never mind the fpr and injectors until you go to the dyno again.

Dyno tuning is incremental.

Sam Lin

Wrong Willard, a different fuel pump won't do a thing for him, he's maxing out injector duty cycle and not fuel pump. Only way to solve that is change fuel pressure or injectors.

Stoichiometric is 14.7:1, and depending on a/f or f/a ratio, higher or lower is rich/lean. Usually, rich is lower, lean is higher. Max power occurs around 12.5-13:1.

Sam

Willard Bridgham 3

I disagree, Sam, he needs more fuel and a higher flow fuel pump will give it to him and keep the injector duty cycle the same.

Sam Lin

Would you like to explain how more fuel is going to get into the cylinders when pressure and injector openings are the same?

Sam

Willard Bridgham 3

As in all larger pumps, pressure is higher, flow is higher.
At equal pressure, flow is higher for larger pumps
At equal flow, pressure is higher for larger pumps
Check some pump curves.........this is characteristic of turbomachinery in general.

Sam Lin

Do you understand how the stock fuel system works? In it, the pump makes zero difference in pressure, and he does not need more pump flow, he needs more injector flow. Do some research before you post.

Sam

Willard Bridgham 3

Yes, I do understand how the fuel system works.

Where do you suggest the pressure/flow in the system comes from?

Let me suggest the pump.....

Sam Lin

Pressure comes from the pump, but the stock pump is already enough to hold even double the stock pressure. The pressure is LIMITED by the fuel pressure regulator, which relieves excess pressure by venting fuel back to the tank. If that is not changed, no pump will ever be able to raise the pressure. This is called a return fuel system, check them out some time.

Sam

Willard Bridgham 3

Back to my point about turbomachinery: larger pump=more flow and more pressure, same piping system.

You should study more about pumps and fluids.