As far as tuning for power is concerned, would tuning for a richer AFR with more timing make more power, or the opposite (leaner AFR's with lower timing)?

Reason I ask... I recently added a few mods and have noticed the car running way leaner than it used to. Pulled a degree or two of timing in some spots it was knocking and it now pulls like an f'n freight train but is running VERY lean at WOT (AFRs stay around 11.8-12 from peak torque up until a little before 7k when it richens up).

I'm not hitting any more than one or two counts of knock (most recent log was one count before peak torque and two ~7400).

My concern is that even though it feels great, I'm not sure how safe it is to be running that lean on 92oct, regardless of the lack of knock. Also, I don't want to lose any power (even though if it'll save my engine's life, I'm all for it).

If I was to richen it up to ~11.5-11.7 at peak torque and taper it down to ~11.1 at 7k and add in some timing, I'm hoping that I'd either retain the same "power" (no time to get on the dyno to really compare, all I have right now is EvoScan's estimation) or even gain a bit with the addition of more timing and at the same time add some reliability... does this seem right?

If this helps any, here's my power mods list (before and after):

Before - TurboXS TBE, Buschur filter, Hallman Pro@~22psi, ETS U/LICP, Walbro 255

Added - eBay O2 housing, Buschur intake pipe

TIA for any help.

 

you shouldn't loose much power by richening it up a bit.

just try it and see

 

try to run a flat 11.5-11.6 afr... safe and will make you smile =-)


Cheers!

 

That's right where I am running my car now. I am going to bring it up to roughly 11.7-11.8 to see if i can have just a touch more fun.. (Although my fun might be pulling the motor soon, he he..)

 

Over compensating for increased timing lead with more fuel is not a good way to go. It will cause, over time, carbon build up in the combustion chamber, top of the pistons and around the valves. Run a consistent AFR in all gears with more conservative timing. As you increase in rpm, your VE will fall drastically. No need to run it richer than peak torque. If anything you will need it to taper up leaner as you increase rpm and boost tapers.
My two cents.

 

I wouldnt call 12:1 VERY lean. I am not sure what you are running for octane there but as long as you dont knock, or knock minimally you are fine.

 

For forced induction:
0.80 Lambda = Rich Best Torque (safe, and nearing peak torque)
0.82 Lambda = Best Torque (absolute maximum torque)

The lambda of air needed to completely burn one pound of pure gasoline is 14.7 lbs. This means that a lambda of 1.0 for 100% gasoline is 14.7AFR

So 1.0 Lambda, for gasoline, is 14.7AFR

This means rich best torque = 0.80 x 14.7 = 11.76 AFR. There is no point in tuning richer than this unless your fuel is so bad, you are getting severe detonation. Otherwise it just makes you slow and wastes gas. Most people tune for 11.5 or 11.7 on pump gas, because it is very safe and makes a lot of torque with little or no detonation.

When it comes to race gas or high octane gasoline, it has much better detonation resistance and you can tune for best torque, or 0.82 x 14.7 = 12.0:1

 

Shamelesscookie,

I won't disagree and I won't accept it as gospel. It makes a good place to start your tuning.

 

err on the rich side, its better to waste a bit of fuel than to put a hole in your piston.

I tune for 11.0 at peak boost tapering to 11.3-11.5 to 6500 rpm then to 11.6 above 6500

thats just my opinion

 

Just to counteract those that are posting rich-biased thoughts (not for argument's sake):

I frequently run 12.3-12.5:1 at 29psi on 93oct with WI at roadraces. My car has perfect compression and runs great. Don't be fooled, I have tons of modifications, but know that 12.5:1 isn't the "Devil". That being said, unless you're into experimenting, the 11.7ish:1 was sound advice.

EDIT: oh yeah, and don't be afraid to taper up to 12:1 or so up top where boost falls off (w/ the stock turbo)

 

What sort of EGTs do you hit. I have run similar AFRs playing with my tune and was getting out of safe AFRs, then again it was also due to lack of timing.

I dont see a reason not to lean the car out as long as you dont knock and you are running safe EGTs.

 

Evo 9s are a different story than the previous ones so those with previous models shouldn't suggest to this guy with an evo9 unless you're suggesting an evo9 number.

I think Honki meant don't be afraid to taper up up top? I agree with others saying this. When your VE drops the rate the fuel burns is slower so some can lean AFR to bring the burn speed back up. (or just increase timing more)

 

Awesome info guys, thanks.

Looks like I'll shoot for ~11.7 all the way through and see if I can't add a little of the timing I had to take out back in. I'll experiement with leaning it a bit up top also to see what happens.

 

I also tune a little rich at peak torque just to keep things safe.

 

I tune for 11.7 across the board. On the dyno you wont see a big difference in power between 11.2 and 11.7 to be honest...maybe a few hp but if the timing is good and there isnt any knock its not like you find 20hp or something between the 2. I prefer a little leaner for the same reasons that DTM listed.

I have tuned at 12:1 on pump with no difference in knock threshhold, and I have tuned at 11.1 and noticed a drop in power on the same car but couldnt add timing to make up for it. Every one is a little different in what it will allow. Fuel is the biggest key since not all 92 or 93 are created equal. You will notice a difference in spool though depending on how lean or rich it is at peak torque. A little leaner on spool up tapering into your AFR across the board is my philosophy.