this is very informative. for the experienced tuners.. what afr during spool up do you prefer? around 12.5 going down to around 11.7 as you hit full boost?

 

Andrew, yeah something in that range is what I employ. I turn lean spool off and control it with just the map. I have experimented with 12.5-12.8 pre spool tapering to 12 by "real" boost and then 11.7 all the rest the way to redline.

 

your afr's are irrelevant to this thread if you are using the extra cooling capacity of water injection. the whole reason to run a richer afr than 12.5:1 is to cool the intake charge and ward off knock.

try running that 12.5:1 and 29 psi boost on just pump gas and let us know how it goes :/

 

Tnx! I'll try that and see what i get.

 

I kind of agree to a point with the statement of "don't be afraid to lean things out a hair towards the upper rpm range". For the average guy on here safety is number 1, especially when having to deal with replacing a motor. That being said though, where I came from in the Honda boost world it was pretty much gospel to run a low to mid 12 afr (no leaner than 12.5afr though) during full boost even on stock internal motors, but at the same time none of those were anywhere close to 29psi. I tend to shoot for 12.5 into boost and have it start to richen up from there to a pretty steady 11.7~ish afr.

 

+1

 

Minimum timing for best torque is what I go with. The advance it takes to get there depends on afr, and many other things but primarily afr.

 

Yo justboosted02, A richer mixture doesnt cool the combustion chamber as much as people might think, if it does, its not enough for a significant difference. a richer mixture makes your burn slower, with that you hit peak cylinder pressure at a later crank angel therefore its a bit more safe. ( hitting peak cylinder pressure at a later crank angel makes it a bit more safe,) Isnt the ideal point at like 14-16*?

 

^exactly what you said. The minimal amount of more gas doesnt cool the cyl as much as people think. Gas has a very low specific heat (meaning it cant absorb very much heat, unlike water), so it will not bring down cyl temps the way most people think. Richer with less timing will actually raise EGT's (cause gas still burns in the exhaust).

 

Agreed.

 

i tune mine for 12.1 at peak torque, and slowly richen it up to 11.5 redline. this give me a +0.4 safety margin incase of crap gas what not.

 

I'm shooting for 11.7 flat... as soon as my wideband sorts it self out ill do another log

 

Leaner fueling does not equal more HP necessarily. I think of Fuel as thermal management of the combustion process. I try not to think of fuel as a way to get more power as is commonly believed. What you want to do is start out on the rich side of where you believe your engine wants to run, and lean your mixture till you come into the "window" of proper fueling. You need to be able to measure power output while your adjusting your fueling so you'll know when you have the correct fueling for your engine. It's a bell curve and you want to be on the rich side of the bell RBT (Rich Best Torque). You do the same thing to find MBT Minimum Best Timing, start on the conservative side and add timing till you hit peak power and then back off - obviously this is all more tricky with knock limited fuels.

Example

AFR DYNO POWER OUTPUT
7.0:1 95 may misfire from being too rich
9.0:1 98
10.0:1 105
10.5:1 110
11.0:1 125
11.5:1 128
12.0:1 130
12.5:1 132 Rich Best Torque
13.0:1 132
13.5:1 131
14.5:1 130
15.0:1 125
16.0:1 120
18.0:1 110
19.0:1 100
20.0:1 95 misfiring from being too lean

Note: the window from about 11:1 - 15:1 power stayed roughly about the same, give or take ~7 hp. Which engine do you think will last longer? hint 11.1

So based on the example I would say for this engine's RBT is at 12.5:1. . I made this example up for the sake of explaining proper fueling but you get the idea. Once you tune your fuel, then you tune your timing. Obviously, you may have to revisit fueling after adjusting ignition timing as well. Also when tuning on higher boost, lower octane fuels, or pushing things to the edge your "window" of proper fueling / ignition timing narrows.


My engine likes 12.2 at spoolup, quickly to 11.5:1 tapering to 11.1:1 at redline with a 25psi spike tapering to 19-20psi.

Why do the OEM's tune cars to run pig rich 9:1 AFR? Richer mixtures burn cooler and equal cooler combustion chamber temps. Cooler combustion temps = engine longevity.

 

i love the analogy of oxygen = girls, fuel = boys
when having a party you always want to make sure their is at least 1 girl for every boy. always invite way more girls than guys.
and like al parties by the end of the night (high RPM) the ratio of girls/boys decreases ( richer) because girls have left with boys and other girls left to go home, all the single geeks boys are left staying around for stupid hopes
hahahhahha

 

So I'm working on getting everything to a flat 11.7 (little bit leaner at peak torque and towards 7500)... Should I wait on doing this until I have a chance to rescale my MAF? I don't have the time right now to do o, but I'm not sure if after rescaling it if I'm going to need to retune the AFR.