building boost at a stand still

[t3rse]

Ok, here's my question: Stutter box, I'm sure you all know what I'm talking about, aka, two-stage rev limiter. How does this build boost? If you are bouncing at, lets say, 5000 rpm, is it the exhaust gases and unspent fuel during the cutout that cause the turbine to spin?

Also, what about retarding the timing dramatically during this. Would this aid in producing boost before providing a load?

[turbovanman²]

Your not bouncing the rpm, its just stable. When I am at the drags, the GN guys 2 foot it and you can hear the turbo spooling and the rpm is stuck at say 3000 rpm-your foot is at the floor, the light goes and they release the rpm lock and boom, there gone.

I get confused about this one, I had to advance my cam to get my stage III wheel to spool so ???????????????

[tryingbe]

t3rse. Auto or Manual are you talking about?

[t3rse]

My friends DSM has a stutter box. It will make 10psi at 5k, but it does bounce. It is only a spark cut, and it doesn't bounce much, but there is a hell of a lot of unspent gas particulate exiting the pipe.

I figured ignition retard in order to produce hotter gasses to artificially load the turbo.

I'll try and make me one, and see how it turns out.

[t3rse]

manual...makes things a little more complicated eh...

[BadAssPerformance]

Boost is usually made under load, but I have seen a couple turbo mopars that will make boost by free revving.

I carefully hold mine at 5k and then floor it when i launch... no boost before launch, but tons after! :thumb:

[Frank]

Myself and Ken can build 6psi on our cars. Just wait till I get the LW intake!


Frank

[87csx2.4]

Ok, here's my question: Stutter box, I'm sure you all know what I'm talking about, aka, two-stage rev limiter. How does this build boost? If you are bouncing at, lets say, 5000 rpm, is it the exhaust gases and unspent fuel during the cutout that cause the turbine to spin?

Also, what about retarding the timing dramatically during this. Would this aid in producing boost before providing a load?To build good boost quick on the line with an auto and say a hybrid 50 trim you have to have a stall of at least 3500 rpm.Ive got my 2 step setup so when you hit the brake the 2 step is on, then I start to spool on pre stage roll in to stage and hammer the throttle still holding the brake.The 2 step kicks in at 4000 rpm by then im sitting at 10 to 12 psi and holding let off the brake and it goes full timing.So your actually building boost before the 2 step kicks in,the 2 step will hold the boost level but also cuts every other cylinder so you dont pull through the traps then the light turns green let off the brake and go full power.2 steps are awesome for the track especially with an auto.

[glhs875]

To build good boost quick on the line with an auto and say a hybrid 50 trim you have to have a stall of at least 3500 rpm.Ive got my 2 step setup so when you hit the brake the 2 step is on, then I start to spool on pre stage roll in to stage and hammer the throttle still holding the brake.The 2 step kicks in at 4000 rpm by then im sitting at 10 to 12 psi and holding let off the brake and it goes full timing.So your actually building boost before the 2 step kicks in,the 2 step will hold the boost level but also cuts every other cylinder so you dont pull through the traps then the light turns green let off the brake and go full power.2 steps are awesome for the track especially with an auto.

Amen!:thumb:

[tryingbe]

Slip the clutch.

[t3rse]

^ good point.

Anyways, I have an SDS standalone comp in my car, which lets me tweak everything. For shits and giggles, I set the revlimiter at 4k today, and bouncing it off of fuel cut, it made about 12psi, at 3k about 8, and 5.5k about 15. I'm going to do a little more research, but I want to see if I can fool my sds unit into cutting the fuel early using a pot switch adjustment, until I let the clutch off of a micro switch which I will install.

oh yeah, it shoots fire when it hits cut, much fun :D

[86Shelby]

oh yeah, it shoots fire when it hits cut, much fun :D

So does my friends WRX. Awesome seeing a 10" flame come shooting out the exhaust.:nod:

[David Bohrer]

I can do it by doing a chop throttle action with the right foot! It took alot of practice but, I am fairly consistent now. I bounce the rpms between 5500-6000 and start to slip the clutch at the last yellow and maintain 5k during slippage and voila! I leave with 5 pounds and have full boost by the end of clutch slippage. Granted full boost in first gear is only 12 psi of boost.

[87csx2.4]

^ good point.

Anyways, I have an SDS standalone comp in my car, which lets me tweak everything. For shits and giggles, I set the revlimiter at 4k today, and bouncing it off of fuel cut, it made about 12psi, at 3k about 8, and 5.5k about 15. I'm going to do a little more research, but I want to see if I can fool my sds unit into cutting the fuel early using a pot switch adjustment, until I let the clutch off of a micro switch which I will install.

oh yeah, it shoots fire when it hits cut, much fun :DWhich sds are you using the em4f you can run with msd dis2.Its got a two stage and hotter spark I got mine off ebay fairly cheap.

[t3rse]

em3f, and I could shell out for for a msd6al (I have a 6a now) so I could put one of the god forsaken pills in it (or cut one up and make a pot switch control), but I don't really have the money now, so I'd rather rig something. I also like bouncing on fuel cut, as it washes down the cylinders with buttloads of fuel and keeps everything nice and rich (you wouldn't think a fuel cutout would do that, but read SDS info).

autometer also makes a box that plugs in between the coil and msd unit for about a 100 with multiple spark cut points and a "test" button that makes the revlimit half of what is set, but once again, these things have to be stupid simple, I just need to figure out how it works.

I also thought about building a serial passthrough to put between the SDS comp and controller to intercept signals and basically hack the damn thing. I could then use another computer to change the fuel maps/timing maps on the fly.

[8valves]

The two step is great, AEM EMS' anti-lag is even better! This is allowing a lot of EVO/DSM guys to launch at 15 + psi on turbos as large as Garrett GT42R's.

It all depends on how much traction you have as well. In my buddy Chad's Integra on street tires we only cut the timing at about 2800-3000 rpms just to get 3 or so psi. Anything higher and it was pointless as the car will just let the tires go immediately.

You need to see exactly how much you can hook right away to determine what rpm to have the cut at.

And yes, leaving all the fuel in it and pulling timing back hard will cause mass flames (and boost) due to the combustion continuing as it exits the manifold and through the pipes. That heat energy is what drives the turbine wheel harder to boost at a standstill.

Aaron Miller

[87csx2.4]

Yeah Ive been able to get close to 15 psi setting my msd at 4200 rpm,Ive only had my car to the track once with slicks.I was afraid I was going to break the input shaft in the trans.Ive got a fix for that though and Im fixing to cut her loose in the spring.:evil:

[t3rse]

What is this fix you speak of?

Honestly, my car won't hook at any boost off the line. I can build 3 psi by holding the throttle at 4k with out blowing fuel through it, and it just smokes the tires. Then again, I only have 3 functional gears right now and my tires are shot...hehe

Right now its more for entertainment: being able to blast a shockwave at mustangs at stoplights.

I am going to go ahead and attempt to build a serial intercept for the SDS. I'll intercept the signals going from the controller to the computer to determine what memory locations hold what data. My plan is to build a simple traction control: I can monitor RPMs and hook an accelerometer to the computer (intercepting one) and calculate fuel requirements or possibly hook a ball valve bypass to the grainger and use a silenoid to control boost from the computer. It will be an interesting project either way.

Thanks for all of your input fellas.

[87csx2.4]

What is this fix you speak of?
904 input shaft from the rwd trans.

[Mario]

So who's running the MDS 6AL with the two step module?

[Speedeuphoria]

I lucked out when I bought my DIS2 of ebay, ended up getting the programable one(didnt know there were differences).

The programable Dis2 has 3 limiters instead of 2 for the regular dis2(max rev limit, burnout limit and launch limit). The difference is the launch limiter wich can pull timing also and progressivly brings the timing back up to what it is set at via a delay(amount of time that you set it for(up to 2.5 seconds in .010 intervals).

So with a trans brake and the dis2 setup you can have great success. Hold a button to activate the launch limiter and trans brake(build boost quickly due to the 2 step and retarded timing), let off the button, trans engages and car starts moving, the timing is still retarded so power is down to a managable level and the timing is brought back progressively. This combined w/ speed based boost control is what should provide great consistent times on any tire.

If you have seen the SMP car and watch the launch you can see what I'm talking about.

[Mario]

Thanks for info. That does look like a better unit. Maybe Aaron will chime in here as well for some additional info.

Hopefully I can get one of these for around $200. Any higher and I think I'll hold off until I go for the aem ems.

[cordes]

I can free rev and get about 3PSI in the omni. I also run the BB code from moparchem.com and the staging mod will build some decent boost. Rob just posted up a cal that will pull timing along with the staging mod. I haven't got it to work yet, but when I do look out!

[Mario]

So maybe I don't need that then....hmm. I'm getting ahead of myself. I need to focus on getting everything together now I guess.

[cordes]

So maybe I don't need that then....hmm. I'm getting ahead of myself. I need to focus on getting everything together now I guess.

For those running stock electronics, I think a 2 step might not be needed. Some are putting out enough boost for a decent launch with just the staging mod. if/when the retard function works also, it will certainly eliminate the need for it.

I would certainly want one if I was not running stock electronics though. It does make a big difference.