What's the ideal A/F vs boost curve look like?

[born2drv]

I'm thinking say:

16 AF @ idle / vaccuum
14 AF @ 0 boost
13.0 @ 5psi
12.5 @ 10psi
11.5 @ 15psi (assuming max boost at 15psi)

?

How do you figure out what is ideal? Is it good enough to vary based on psi or should you vary based on load/rpm instead? Some combination of the 2? Any help would be appreciated!

 

[robbo185]

14.5-15 is good for idle/cruising
11.5-low 12's is good for wot

i base mine on just making the right curve for wot.....tune for the a/f ratio you want. 11.8 for me and i only tune 3000 rpm and above because ecu takes care of anything lower than 70% throttle and it will make it as close to 14.8 as possible

 

[dbsupra90]

idle and cruise mid 14:1 is perfect. the ecu will do this for you in closed loop.

open loop off boost i usually shoot for mid 12:1 to 13:1. this is safe off boost and will help spool.

under boost i shoot for 11.5-11.8:1

i use this method whether its 5psi or 25psi, 100rwhp or 1,000rwhp.

 

[MK3Brent]

Hehe Dave...
"it doesn't matter if it's 5 pounds or 25 pounds...
AFR's are AFR's"

 

[Rajunz]

idle and cruise mid 14:1 is perfect. the ecu will do this for you in closed loop.

open loop off boost i usually shoot for mid 12:1 to 13:1. this is safe off boost and will help spool.

under boost i shoot for 11.5-11.8:1

i use this method whether its 5psi or 25psi, 100rwhp or 1,000rwhp.

I'm curious about this statement......................what would be considered open loop off boost
. I always thought it went into open loop under boost???

 

[tissimo]

I tuned 14.7-16 in low vac areas..

at 0 psi I go for 13.0-13.5
0-5 psi taper to 12.5
5-8 go 12.5 tapered to my target A/f under boost
8+ target a/f (11.3 on my personaly car.. i go concervative)

 

[cjsupra90]

I'm curious about this statement......................what would be considered open loop off boost
. I always thought it went into open loop under boost???

Yes, it does go into open loop while under boost, but ECU's kick out of closed loop control above a certian throttle point and a certian engine load. Typically this change over point is in the 5 to 8 in/hg vacuum range (75 to 85 kPa) and above usually 60 to 70% throttle.

 

[dbsupra90]

I'm curious about this statement......................what would be considered open loop off boost
. I always thought it went into open loop under boost???

thats funny. i didnt realize this was an old thread and started reading the responses. i saw mine and thought hey thats exactly how i do it! oh wait, that is me lol.

anyway, anytime you are at 75%+ throttle and not boosting i call off boost open loop. example- say im leaving a stoplight and 1500 i hammer down. from 1500-3200 rpm im not making boost (or just starting to) so i tune a little more lean.