Air Fuel Ratio Discussion...

[S197 GT]

I figured Air Fuel Ratios would be a good topic to discuss.

Some of the things I'd like to look into are:

• How Lean is Too Lean
• How Rich is Too Rich
• What are Contributing Factors of Being Rich/Lean
• What are Things to Troubleshoot in a Rich/Lean Condition
• What are Acceptable Ranges in Being Rich/Lean
• What are the Negative Effects of Being Too Rich/Lean
• Air Fuel Ratios at: Idle, Cruise, Part Throttle, Wide Open Throttle

 

[travelers]

That it is. Now we need Dyno Joe to chime in here with his vast knowledge of A/F.

 

[cekim]

I figured Air Fuel Ratios would be a good topic to discuss.

Some of the things I'd like to look into are:

• How Lean is Too Lean
• How Rich is Too Rich

at WOT:
For N/A ~12-13
For FI ~11-12 (more boost goes towards 11 - less towards 12)

• What are Contributing Factors of Being Rich/Lean

Rich = too much fuel
lean = too much air
J/K - sorry had to...

other than "tune" calling for the wrong thing...:
1. lean - unmetered air entering the intake (air leaking in after the MAF in the intake path)
2. lean - bad/mis calibrated MAF
3. lean - too much timing
4. lean - low fuel pressure
5. rich - bad/mis calibrated MAF
6. rich - fouled plug (not firing/burning the gas)

• What are Things to Troubleshoot in a Rich/Lean Condition

See above:
1. tune wrong (just plain wrong, or failed to account for IAT?)
2. MAF bad/mis-calibrated
3. missing clynders
4. insufficient fuel flow/pressure
5. air leaks in intake after MAF
6. engine temperature

• What are Acceptable Ranges in Being Rich/Lean

See ranges at top for WOT - when in closed loop (idle/cruise), the PCM will try to bring you up to ~14 - 14.7. Of course the A/F will fluctuate any time you change the pedal position rapidly - all of the values stated thus far are typical "targets" for a given state (closed loop or WOT).

• What are the Negative Effects of Being Too Rich/Lean

Rich:
fouled plugs, wash cylinders (break down lubrication of rings and grind cylnder walls), foul cats, generally contaminate oil/lubrication

Lean:
overheat engine, burn piston/valve/spark plug components, detonate (break everything... )

• Air Fuel Ratios at: Idle, Cruise, Part Throttle, Wide Open Throttle

See above - WOT is different for N/A vs FI. At part throttle/idle/cruise you are closed loop and will be high 13 to mid 14's

(to get around "post too short")

 

[S197 GT]

Thanks for the reply Mike...

Can you elaborate more on what is too rich or too lean??

Reason I'm asking is that I'm seeing 10.2-10.8 at WOT right now. So I'm running rich. I'd like to know where is the cutoff for an acceptable rich condition?

Is 10.2 too rich? I'd like it up around 11.2-11.5.

 

[Hawgman]

11.5 to 12.5 is the "accepted" safe range for a FI car at WOT, but it is not the steadfast rule. I know people that run leaner than that in the higher RPM ranges and it makes me cringe. But they do their own tuning and swear by their tuning and research. RoyB is running in the mid to high 13s on his car.

 

[cekim]

Thanks for the reply Mike...

Can you elaborate more on what is too rich or too lean??

Reason I'm asking is that I'm seeing 10.2-10.8 at WOT right now. So I'm running rich. I'd like to know where is the cutoff for an acceptable rich condition?

Is 10.2 too rich? I'd like it up around 11.2-11.5.

Assuming there aren't any instrumentation errors (i.e. your A/F is being measured reported correctly, wideband is calibrated etc... )

Then I would say that 10.2 is "too rich"...

Do you get black smoke when you stomp on it?

 

[cekim]

11.5 to 12.5 is the "accepted" safe range for a FI car at WOT, but it is not the steadfast rule. I know people that run leaner than that in the higher RPM ranges and it makes me cringe. But they do their own tuning and swear by their tuning and research. RoyB is running in the mid to high 13s on his car.

They usually also do custom head work too...

Some fascinating reading out there from the mid 80's and onward...

 

[S197 GT]

Assuming there aren't any instrumentation errors (i.e. your A/F is being measured reported correctly, wideband is calibrated etc... )

Then I would say that 10.2 is "too rich"...

Do you get black smoke when you stomp on it?

Nope, no smoke when I nail it.

 

[cheftjpeck]

cool very informative

 

[cekim]

Nope, no smoke when I nail it.

hmm, well we should get Joe to weigh in, but I guess I would expect some bus-like behavior at the tail-pipe as you approach 10...

Go yank a plug and get some pics...

Cats?

 

[S197 GT]

hmm, well we should get Joe to weigh in, but I guess I would expect some bus-like behavior at the tail-pipe as you approach 10...

Go yank a plug and get some pics...

Cats?

Nope, no badass deisel clouds of smoke!

I just got some new plugs and I was going to pull the current ones to check them out next weekend.

Nope, I don't have cats.

 

[MikeVistaBlue06]

I figured Air Fuel Ratios would be a good topic to discuss.

• How Lean is Too Lean

Anything leaner than 14.7:1; 14.7:1 is stoichiometric.

• How Rich is Too Rich

Anything that is numerically lower than 11:1

• What are Contributing Factors of Being Rich/Lean

Rich: Too much gas or not enough air

Lean: To little gas or too much air (usually the first one)

• What are Things to Troubleshoot in a Rich/Lean Condition

Rich: spark plugs will have a dry black soot on them--ditto for the tailpipes after a good cruise. When you romp it it will bellow black smoke.

Lean: Spark plugs will look too clean or may "blister." Detonation or spark knock (BADDDDDD & IT KILLS ENGINES!!!). No residue at all in the tailpipes. Backfire.

• What are Acceptable Ranges in Being Rich/Lean

Cruising (Rich): 14:1
WOT (Rich): 11:1

Lean: You don't want to go there! Better a tad rich than lean IMHO!

• What are the Negative Effects of Being Too Rich/Lean

Rich: Fouling spark plugs. Overheating catalytic converter (also plugging it up!). "James Bond" black cloud effect when you romp it. Killing your gas mileage. Poor driveability if it is really rich. Oil dilution if it is really rich (gasoline running by piston rings).

Lean: Blowing your engine (burn pistons, detonation-->busted piston and/or rods!)!! Poor driveability.

• Air Fuel Ratios at: Idle, Cruise, Part Throttle, Wide Open Throttle

Idle: 14.7:1
Cruise: 14.7:1
Part Throttle (same as cruise) 14:7:1
WOT: 11:1

Hope this helps.

Mike

 

[Slofoot]

Nick, I don't think you are rich to the point of hurting anything but you are leaving quite a few ponies on the table especially at your boost level. For example, after installing my GT500 pumps I ran at the track quite a bit running 11.50's to 11.60's. I made a couple of pulls to check my A/F after a month or so and it was in the lower 10's at WOT. Joe at Dynospeed pulled some fuel to get me to 11.5-11.8 at WOT and I went to consistent 11.30's and picked up around 20 rwhp and about the same tq numbers as well.

 

[MikeVistaBlue06]

BTW, My dad used to intentionally set his carb rich at idle. He'd then install sparkplugs at the end of the tailpipes and be able to spark'em when he was cruisin and throw out 2ft long plumes of flame, or so he told me!

He said it was the shit at nightime!

Mike

 

[S197 GT]

Thanks guys for your input.

Kevin, I know I'm losing out on some horses, which is why I've been trying to make some time to meet with Adam and get this dialed in.

He made me a tune that gave me a lot more power, but it was hesitating, so if only I could get that tune dialed in! It would hesitate, but then it would pull like a freight train!!!

 

[travelers]

BTW, My dad used to intentionally set his carb rich at idle. He'd then install sparkplugs at the end of the tailpipes and be able to spark'em when he was cruisin and throw out 2ft long plumes of flame, or so he told me!

He said it was the shit at nightime!

Mike

The old lead sleds had them. They were really cool at night. You got to see it.

 

[ZmanM3]

Very informative thread.