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Old 01-09-2011, 12:02 PM   #1
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Default Launch Control. Cut fuel or cut spark?

When setting up launch control, I am not sure if I should configure it to cut extra spark events or cut extra fuel events. From what I've read, either can work. If I cut spark, then afterfire can build boost. If I cut fuel, the enleanment will raise my EGTs and build some boost.

Cutting spark seems better to me- I have not heard of anyone saying that they wrecked their turbines or valves from afterfire.

What are your thoughts? I only want to build 6psi or so.
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Old 01-09-2011, 12:12 PM   #2
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You have to cut spark first and then fuel shortly after. You need the fuel to get farther into the exhaust and then ignite to create boost. I'm making 5PSI and it holds at 4500RPM. Used it all summer, just make sure you don't sit there for a long time because your exhaust gas temps are going to go through the roof.
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Old 01-09-2011, 12:27 PM   #3
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Cut fuel shortly after meaning in higher RPMs? Is this so I can hold at an RPM WOT?
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Old 01-09-2011, 12:41 PM   #4
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Yes cut at a slightly higher RPM. I think I have ignition cut at 4300rpm and fuel cut at 4500rpm (don't quote me on that, I'd have to look at my tune which is on my laptop). At least on the AEM EMS, the point of launch control is to hold the car at a steady RPM on WOT, and to make boost while doing it. I use my car for drag racing so this ensures I get the same launch every time. It's also a fantastic way to leave a strip of rubber down the street. Oh also, you'll need to have some way to disengage/engage the launch control. I hooked my clutch switch up to the AEM and put a little toggle switch inbetween near my shifter. So if the toggle switch is on and the clutch is in, launch control is engaged. Once the clutch comes out it goes out of LC mode and takes off.
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Old 01-09-2011, 01:26 PM   #5
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I cut spark and fuel and made 4psi. I would then step off the clutch and do a huuuuuuuge burnout the entire way through first gear.

Cutting spark only just makes a bunch of noise and builds way too much boost.
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Old 01-09-2011, 11:21 PM   #6
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I cut fuel and spark from 6 of 7 events at the same RPM. at small throttle angles it's very quiet. at larger ones it gets noisier.

like sav says, cutting (most) spark is noisy as hell with backfires.
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Old 01-10-2011, 08:42 PM   #7
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Hydra 2.6 has a RPM x %age cut table for fuel and spark launch control. Alas, 2.5 was easier to set up :(

I got it to build about 3psi with 80% spark cut 60%fuel cut. AFR is 20:1 when building boost but **** that shouldn't be bad because there's no spark either.

I did not get any afterfires which is what I think I need to build more boost. I also need afterfires to impress my passengers, nearby small children, and also to induce the west baltimore slum denizens to duck and cover.
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