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purveyor of lightness
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Discussion Starter #1
Ok nine years ago I designed my own launch control system with a Netduino, the EFI 1.2 ECU and wheelspeed sensors. Basically I had two maps on the EFI - 9160rpm rev limit and 2500rpm rev limit... switchable via an solid state relay. If the system was activated then the map would be set for the lower rev limit for 10 seconds - or until the car reached 6mph.... then it would swap to the 9k map.

Now I have the stock ECU running FastWorks and unfortunately I don't have the luxury of having external ECU rev limit control...

I stumbled across this piece of kit:
MSD 4350 Universal Launch Master, Coil-on-Plug 4-Cylinder Engines)

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It appears to tie into all four ignition signal wires (brown) as inputs and will on command either disconnect/ground the common +12v coil output line to prevent ignition.

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The question I have is what effect on the coils / ECU will this have if the switched +12volts (coming off fuse R7 in the engine bay) is pulsed/interrupted rapidly to limit revs?

I'd use a pushbutton for the initial testing but I'd later toss an Arduino or equivalent to monitor vehicle speed / show status on an RGB LED:
Red = ignition on, no rpm
Green = ready to launch / rev limited (engine running, 0 mph)
Blue = We're moving more than 6 mph - no limiter

Does this seems like a reasonable/affordable way to effect launch control? It's quite difficult to get a consistent launch with the RevX supercharger. Wheelspin/clutch burn is my enemy! Very delicate balance...

Just thinking out loud on my Dad's day :)
 

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I've designed my own traction control systems and use to sell them to racers. At the time, I was also playing around with launch control for hill climb cars. The problem I ran into with cutting the ignition system is that you still have fuel going through the system. This can create some very interesting problems when it hits the hot exhaust. Since I only had systems that were running older ignition systems; MSD, distributors and carbs, I could not get control over the fuel system. If I were to try it with a fuel injection system, I would cut the injectors to regulate the RPMs. You could install some FETs, inline with the signal to the injectors, to act as enable switches. If you do this with the coils, you will need much larger FETs. When playing around with ignition coils, I found they would draw between 30 - 50 amps to recharge.

Later,
Eldon
 

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purveyor of lightness
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Discussion Starter #3
Eldon, well it looks like fuse R7 (10amp) controls the +12v supply to both ignitors AND fuel injectors... It would be a very easy test to try the intercept there... it would kill both spark and fuel. In the meantime I think I'll just pull R7 and plunk my Fluke 87 DVM inline to see what type of current draw we're talking about.
 

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Eldon, well it looks like fuse R7 (10amp) controls the +12v supply to both ignitors AND fuel injectors... It would be a very easy test to try the intercept there... it would kill both spark and fuel. In the meantime I think I'll just pull R7 and plunk my Fluke 87 DVM inline to see what type of current draw we're talking about.
My first field engineer in the Air Force told me "There's a Fluke, and there's everything else". I've never owned anything else.

San
 

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David, If R7 controls both then that would be a good place to start. The old rule of thumb for MSD ignitions was 1 amp per 1000 RPM. That was average current and not instantaneous. The 30 - 50 amps only last for a few milliseconds which means that your DVM is not going to register the actual current.

Later,
Eldon
 

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Discussion Starter #6
I'm sure that combining the ignition/fuel cutoff will work fine but now I'm worried about the ECU throwing all sorts of codes, most notably P0351-0354 ignition coil feedback (yellow & black wires). I know that FastWorks can disable certain code reporting - just not sure it can disable all 15... or if I want it to...

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David,
From what I understand, the ECU has to see the fault for X times in a row or X times over a period attempts. So, the real question is how long will your circuit be disabling the ignition/fuel circuit. I have to agree, you might start to get several codes that are because of you.
Later,
Eldon
 

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I did launch control for several pro race series (le mans, American le mans, Pirelli World Challenge, etc), and this system is too simple to be worth the driveline damage in my opinion. You should use a flat rpm limit at first but then go to some sort of slip control (rpm vs vehicle speed, wheel speed vs. vehicle speed) for the rest of the pull.

Also, if you have a stock ECU, I'd wager my left nut this will through a code or two. The worst part about a persistent check engine light is it means you can potentially ignore new problems because you think it is the usual one.

If you look at power to weight of the Tesla P100 vs many other cars that are slower to 60mph, the difference comes entirely down to traction management. Many high performance cars can spin their tires through 60mph, so good launch control is the difference.
 

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I have to agree. This is why I was working on launch control being integrated in to the traction control system.
Later,
Eldon
 

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I have to agree. This is why I was working on launch control being integrated in to the traction control system.
Later,
Eldon
Yeah, for an NA or SC car that detail is why I think the kit above would not be a smart use of money. For turbo cars, that fuel in the exhaust you mentioned several posts up becomes a nice little afterburner since the throttle is WOT, so these two-step kits are great for spooling up big turbos, but that's where I see the sole benefit, not traction management.
 

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Raw fuel in the exhaust of a race car just makes some noise and flames. I do not believe that the CAT is going to like seeing that much raw fuel, let alone that you have a hot enough source to create detonation. You could be in for some fairly loud noises. ;-)
Later,
Eldon
 

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Raw fuel in the exhaust of a race car just makes some noise and flames. I do not believe that the CAT is going to like seeing that much raw fuel, let alone that you have a hot enough source to create detonation. You could be in for some fairly loud noises. ;-)
Later,
Eldon
The heat source comes from retarded timing on the true systems (but yeah, none of the hardware likes it for long so that's why you only use it for launch), and the one OP referred definitely is not in that category.
 

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@cyow5 My systems had the choice of timing retard or a non-repeating cylinder missfire. As long as you had good exhaust valves, the timing retard was the least problematic. Once you start missfiring a motor, there are several things that start coming in to play. One of the funest ones is screwing up multispark systems. Which is why on the MSD boxes, I went to cutting the signal to the coil instead of cutting the signal to the ignition box. It is interesting to see where the rotor will arc to inside of a normal distributor system. Not always where you thought which can lead to minor explosions in the exhaust system.
Later,
Eldon
 

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@cyow5 My systems had the choice of timing retard or a non-repeating cylinder missfire. As long as you had good exhaust valves, the timing retard was the least problematic. Once you start missfiring a motor, there are several things that start coming in to play. One of the funest ones is screwing up multispark systems. Which is why on the MSD boxes, I went to cutting the signal to the coil instead of cutting the signal to the ignition box. It is interesting to see where the rotor will arc to inside of a normal distributor system. Not always where you thought which can lead to minor explosions in the exhaust system.
Later,
Eldon
Haha, good ol' MSD boxes. I had one with a kill switch in my '94 full size blazer. If the cylinders parked juuuuust right, flipping the kill switch on would discharge the caps, fire a spark plug, and if the intake valve was open, it would backfire through the manifold and blow off a specific vacuum hose. Those whole chain of events happened multiple times. At first I didn't notice the loose hose, and it actually sucked enough air through to continue to diesel terribly while it burned the remainder of the fuel that was in the manifold. TBI would drench the intake manifold, and it would sit there clattering until it burned out. Fun truck. I miss it, haha.

Going somewhat back on topic, I worked with a twin turbo 928 once where the guy was adamant about achieving a factory-low idle despite the fact he didn't have an idle air solenoid. To prove a point, I pulled enough spark to get it to idle at about 800rpm, and the headers turned immediately cherry-red. He got used to the idea of a higher idle pretty quickly after that.
 
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