Setting the launch control in MPTune

[Force Fed Mopar]

Is there a scientific way of figuring out which spark cut fraction to use, or is it just trial and error for each engine? My 2.5 is blowing through the base setting of 4k rpm and a 5/7 spark cut.

[ShelGame]

I think it's trial and error. With a lot of anti-lag, and building boost, I think it's going to be difficult to keep the RPM under control @ WOT. If necessary, we can increase the fractions available to cut more spark events.

On my car, with a Mitsu turbo, I can't go WOT and keep the RPM under control. It starts building boost and blows past the limiter.

I also had the idea to get rid of the user-selectable fraction and have it be adaptive. It would then keep increasing the fraction until it gets the RPM in control.

[turbovanman²]

What's a good baseline for setting a staging limiter for my van? Do I pick spark or fuel cut out and I want bang bang, :nod:

[wheming]

Is there any risk of damage with those? The bang bang video seems pretty violent at least on the exhaust. What is going on in the cylinder & turbine housing during those events? Just so severely retarded that it fires when the exhaust valve opens?
I'd like to know more, and clear up my ignorance of it.

[ShelGame]

What's a good baseline for setting a staging limiter for my van? Do I pick spark or fuel cut out and I want bang bang, :nod:

Bang-Bang only works with spark cut.

I'd start with 5/7 spark cut, -4 deg antilag, have the antilag RPM set about 6-800 rpm lower than your staging rpm, cutoff @ 2mph.

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Is there any risk of damage with those? The bang bang video seems pretty violent at least on the exhaust. What is going on in the cylinder & turbine housing during those events? Just so severely retarded that it fires when the exhaust valve opens?
I'd like to know more, and clear up my ignorance of it.

Yes, probably.

The spark is cut, but the fuel is not. When the spark is turned back on, it is retarded to the setpoint, and as a result much of the combustion happens in the exhaust manifold. It's great for spooling (and breaking, as you can imagine) turbos.

Use at your own risk.

[wheming]

Thanks for the explanation.

[zin]

I also had the idea to get rid of the user-selectable fraction and have it be adaptive. It would then keep increasing the fraction until it gets the RPM in control.

I think this is the best option, not enough folks know what to do or how changing this option would be of benefit. Making it "automatic" would encourage its use more.

Mike

[ShelGame]

I think this is the best option, not enough folks know what to do or how changing this option would be of benefit. Making it "automatic" would encourage its use more.

Mike

As soon as I get the GLH (aka, BoostButton development car) done, I'll try it.

[turbovanman²]

Hmmmm, thanks.

[Ondonti]

Its pretty easy to tune, especially if you creep into making it work like Shelgame posted.

Bang Bang is rough, especially if you get aggressive with it. The last two times I have activated mine in the Junkyard, I blew my exhaust apart. When I had first set it up, I was open downpipe. Since then I pulled off the turbo and band clamped the full exhaust together. I am worried that if the exhaust was welded it would still break apart. Mine is still set to cutting 4/5 events which also results in backfires if you flatshift (Megasquirt).

Safe for your parts setup is not bang bang, but whatever is able to control rpms and then you can think about antilag. I don't need boost to leave hard and if you want to protect axles you will be slipping the clutch enough to build boost.

I am not sure if the actual bang hurts the turbo like it does welds on the exhaust but excessive heat is not a friend of your turbo. Bigtime rally racing or open wheel turbos that go through very high temps are not made of the same materials as we all use. Thinking the bearings on the your turbo could see some unhappiness if the bang bang is strong enough to break the oil film. Who knows about that. Gonna be application (oil pressure, etc) specific too.

BTW, I have heard that electronic cutouts do not like antilag (proably when closed) and I would assume aluminum exhaust might be unhappy. I have not put in the research to really say. I find this depressing. :(

[22shelby]

Sorry to bring back an old thread but a question to add to this.. my launch control always seems to be activated below the cut of mph.. can be sitting in park.. all enabling switches off (brake switch, ac, cruise..) have no effet.. just Rev the engine up and it's active... do I need to set the mph to 0 for the switches to activate the LC?

[ShelGame]

If you have no switches set, it will cutoff on ONLY MPH. So, yes, it will be on anytime below the cutoff speed. If you want to be able to turn it on/off, set a switch and wire it in. Then you can enable/disable the launch control when you want.

[22shelby]

Ahh ok.. simply checking the brake switch flag won't switch it on or off... if I want it on the brake switch I have to wire it into the sbec harness?? Is there a dedicated pin on the 60 way for it? I'm running an auto... 91 sbec...

[ShelGame]

No, if you select the brake switch, the staging limiter will be active only when the brake pedal is pressed.

Though, there seems to be an issue with that in the SBEC. Not sure why, but it doesn't always work right.

[22shelby]

Yeah.. even when I select just the brake switch the 2 step is alway active.. I'm going to play with it tonight.. try differ switches... plus I need to fix my speed sensor... it's putting out some real wierd random outputs...thanks for clarifying for me (us) Rob!!

[shackwrrr]

I just removed my turbo after extensive use of the bang bang limiter with lots of spark retard and the turbo side to side play is not much more than when I installed the turbo but there is a lot more in/out play than before. I believe that on a larger turbo this would be less of an issue.

You can set the bang bang limiter up but use very little spark retard and the rpm control will be much better without hurting the turbo. The only way I get it real harsh is to use -16 degrees of timing. If you set it to 0 there will be no damage to the turbo and rpm's will stay steady without pushing through the limiter.

[22shelby]

This right here is great info!!!