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Old 05-28-2006, 03:50 AM   #1
gaby
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Default Launch Control

Anyone using launch control?
If so , with the ignition or fuel cut and what rpms?
I try mine with my set up (18g) and Created 8psi of boost at 4500 rpms.
before the burn, yes, I do have an STI tranny.
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Old 05-28-2006, 01:21 PM   #2
wrxpeed
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Yes i use it. Use fuel cut unless you're spraying. your clutch and Drivetrain will hate you, just a warning.

I rock LC on a stock clutch and tranny in an '02, not a single problem, its all how you drive. I launch on little boost though, maybe 2-5 PSI.
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Old 05-30-2006, 04:56 PM   #3
ride5000
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fuel cut for sure.

i've been using it for years. stock clutches help.

try 5500 rpms..
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Old 05-31-2006, 01:27 AM   #4
gaby
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Good deal. Thanks.
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Old 05-31-2006, 02:04 AM   #5
gaby
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Good deal. Thanks.
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Old 06-01-2006, 09:02 AM   #6
MRF582
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Fuel cut vs Ignition cut. What are the pros and cons? The only thing I think I know is that fuel cut has a chance of leaning out the motor during the 'fuel cut' and can cause severe detonation.
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Old 06-01-2006, 11:39 AM   #7
mick_the_ginge
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Yes the motor goes lean using fuel cut but as it only happens when you press the throttle the engine is under little to no load so it is not that much of an issue.

If you can live with HUGE after fire then use ignition cut. However I have seen 40 counts of knock from the bang from the after fire. Yuck. Personally I run fuel cut, don't use it for launching, just flat foot shifting.
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Old 06-01-2006, 12:41 PM   #8
jstbstn
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I've tried fuel cut but haven't played with ignition cut yet. I did notice with fuel cut that the next couple lines of datalog are scary lean... should this be a worry or not? I didn't see any knock when I had it turned on but it was only for a couple pulls.
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Old 06-01-2006, 03:35 PM   #9
gaby
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So you guys have been sucesfull with the flat foot shifting, at what rpms?
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Old 06-01-2006, 06:32 PM   #10
Lost_Pete
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The way injection launch control works is that it cuts all the fuel to various cylinders when you hit the RPM limit. So a cylinder that has all the fuel cut just pumps air. The other cylinders that are running have their proper allocation of fuel. However this excess air will cause any O2 sensor to indicate that the engine is running lean.
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Old 06-01-2006, 08:53 PM   #11
MRF582
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^^ So it seems like fuel cut is not damaging to the engine even if the 02 sensor indicates a lean AF.

Will the ECU stop injector flow as soon as fuel cut is hit even if an injector to a particular cylinder is the middle of spraying? Or will it stop the next injector in line from spraying. If it's the latter, that would mean fuel cut is not any more or any less damaging than ignition cut with regard to air/fuel.
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Old 06-01-2006, 10:10 PM   #12
Lost_Pete
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Both the ECU and the UTEC only stop complete cycles of injector pulses. i.e. It doesn't stop the injectors part way through their injector duration (cycle)

In addition the cylinders that are being fuel cut are rotated. i.e. It is not always the same cylinder.

regards
Pete
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Old 06-01-2006, 10:45 PM   #13
MRF582
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Thanks Pete. That's cleared up.
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Old 06-01-2006, 11:03 PM   #14
jstbstn
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so in essence it's a false lean condition and down time to get a proper reading back at the sensor by moving the air out of the pipe and waiting for actual exhaust gas to reach the sensor again?
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Old 06-02-2006, 08:38 AM   #15
ride5000
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yes.

you cannot have detonation if there is no fuel in the chamber. compressed air has pretty high octane.

and fuel cut is SAFER than ignition cut due to the lack of afterfire which can backpressure the exhaust valves and unload the lifter, which then drops a shim in your valvetrain.

always use fuel cut unless you MUST use ign. cut. jm2c.

ken
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