stutterbox launch boost with AVC-R bc

[92tsiawd84]

I installed an Apexi AVC-R bc tonight but I haven't had much time to screw around with it. I probly am not going to mess with it until I get my boost creep fixed though. I was thinking tonight about the scramble setting. I was wondering if I could hook it up to my cruise control switch (like my stutterbox) and it let me build more boost before I launch. I was thinking of having my scramble setting around 25-30psi so I will hold ~17psi on the stutter box at the line. Then, when the clutch is released, it would jump back to my regular setting of 17psi and I will have full boost off the line. Could this work? If not, how would I build more boost on the line with my stutterbox.

 

[92tsiawd84]

BTW, it is a msd dis2 I am using the stutterbox feature for.

 

[DSM90AWD]

You won't get that much boost from studderboxing (new word ). Boost is limited by engine load.. and with the clutch in.. load is virtually 0. If you were to slip the clutch a little and hold the brake.. could get more boost (at the expense of a clutch).

The boost controller regulates boost in excess of a specified value. In "studderbox" mode.. your W/G is closed so the controller would have no impact.

BTW.. on my car I get ~5psi at the intake manifold studderboxing at 5500 RPM.

 

[kpt4321]

The load is more than zero, because it must have some load if it is building boost. The way the stutterbox works is designed to load up the engine, to some degree.

However, you have the right idea. When stutterboxing, the boost is determined by engine load, and is going to (usually) be below 8 or 10 psi, depending on the setup (small turbo = more boost). That means that your fancy boost controller won't help you at all.

Also, even if you could, I don't think you would want 17 psi when you launched. Without a stutterbox, building only a couple psi due to clutch-slip, I could EASILY get my car sideways out of the box. I can imagine how nasty 17 psi would be, you probably wouldn't fare so well.

 

[DSMJim]

Originally posted by kpt4321
The load is more than zero, because it must have some load if it is building boost. The way the stutterbox works is designed to load up the engine, to some degree.

Acctually there is still no load, but what is happening is what the rally guys call bang bang, just a little different..

What your two step is doing is dropping spark from 1 cylinder every firing rotation. So that cylinder is not firing which is what keeps your motor from accelerating to a higher RPM even though you have the gas to the floor. WHat happens after that cylinder goes though all 4 strokes and doesn't fire is a mixture of gas and air is shot out the exhaust port into your exhaust manifold. The mixture then lights inside your manifold because it's so hot and creates heat and pressure there which in turn spools up your turbo. Baiscally your turning your exhaust manifold into a combustion chamber and the end result is it spools your turbo with no load on the motor. This is ok to do for a very short period of time however it's very hard on turbo manifolds and turbo's, but for the short period of time we do it in drag racing it hardly matters.

What happens on rally cars why you hear the pop pop pop when they go around corners is their cars are setup to retard timing very heavily when they are off the gas and increase the injector pulse width. What happens is gas is getting sprayed in, but the spark is coming so late that the flamefront shoots out the exhaust port litterally igniting in the exhaust manifold (like whats happening with us using a stutterbox) and causing the turbo to spool, but they get 20psi of spool at idle and off throttle (or whatever they set it to as it's cockpit adjustable) so they have instant throttle responce coming around a corner. It's pretty cool stuff. If anybody can clairfy that a bit better go for it, im just going off memory from what I have learnt a few years ago. I heard that its so hard on the manifold and turbo that those parts generally last 1 race and they are totally shot from all the heat.