How To: SAFC Boost Hack

First of all, boost SAFC is a hack. It's a hack in a sense that you're not using equipment as it was intended.

Apexi intended the SAFC to be used with a throttle signal. That's fine and dandy if all you do is idle and zoom around at full throttle. That is not the case with a turbo specv (or any turbo vehicle for that matter).

In a turbo vehicle, the manifold pressure can vary at the same throttle position wildly. For example, at 30% throttle one can be at full boost on the highway, and one can be at 5 inches of vacuum in 1st gear accelerating. This creates a tuning nightmare.

SAFC is a very simple device, it has 2 maps (hi and lo), 2 load points (hi throttle and lo throttle). Below lo throttle, only low map is used, above hi throttle, high map is used, the corrections are interpolated between the low and high throttle points.

BOOST safc takes the map switching control away from your foot and places it upon the manifold pressure to switch maps. Manifold pressure is a WAY better load signal than throttle as it actually reflects what the engine is doing, instead of what your foot is doing. Way you set it up is simple, you take a MAP sensor (3 bar gm, your electronic boost gauge sender, zt2 boost sensor, some boost controllers have a remote map sensor) and hook it up to safc's throttle input.

if everything went successful, throttle signal will read above 0 when the engine is off, it will read close to 0 when the engine is idling, and it will read some arbitrary value once you are in boost. For NA folks, the engine off throttle value and full throttle value will be the same, because there is no vacuum under full throttle (well, SOME, but we'll say there is none).

Now that you have it wired up and it seems to work, you need to pick high and low throttle points. This is also rather simple.

Low point will be the "engine off" throttle value, or a couple of percent below it.

High point can be anything above the low point. more explanation on this below.

Ideally, the high point will be the highest level of boost the engine will see with your tune.

By bringing HIGH point closer LOW point, you are changing how the engine will behave in part boost, this is something you will need to determine by experimenting as your setup is likely to be different from someone else's.

at first you can set the HIGH point about 5% above low point, this is a safe setting. for now. This way all of the corrections are applied completely once the HIGH point is reached (and it will be reached way before full boost, so that's good).

hopefully others will chime in to tell me if i fucked something up, but that's the gist of it.