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Old 11-22-2007, 01:10 AM   #1
Teh Legacy
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Default Launch Control - Fuel vs. Ignition Cut.

I did a bit of searching, but I didn't come up with a clear answer. What are the pros and cons of going with the different types of launch control? I am not running Nitrous or Methanol, so would it hurt to run ignition cut? Does one provide better performance over the other?
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Old 11-22-2007, 11:51 AM   #2
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they say fuel cut is safer for your engine... thats what I use
ignition cut sounds way loud and agressive.

Also, theres some issue when using nitrous, that you cant use
one of them... its in the manual!

Last edited by lcesardo; 11-22-2007 at 12:01 PM.
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Old 11-22-2007, 11:56 AM   #3
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Ignition cut is more fun it generates more boost and makes a lot of noise but is hard on your engine and exhaust system. I see 20psi+ between shifts.

Injector cut is plenty for me... holds 14psi+ between shifts and generates something like 8psi from a dig.
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Old 11-22-2007, 12:08 PM   #4
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If you aren't using nitrous, you fuel cut. It's not as harsh on the engine, header, turbo, etc as you aren't dumping all the unburnt fuel into the exhaust.

If you are using nitrous, you need to use ignition cut. Think about running nitrous...you need to add fuel with it or things go boom! Now think about using fuel cut with nitrous....
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Old 11-22-2007, 05:51 PM   #5
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Will ignition cut hurt the engine if it's built? (Weisco coated pistons, Eagle rods, ARP head studs, etc.) The exhaust is catless, so I'm not particularly worried about clogging the cats. Exhaust setup is a wrapped Perrin EL header and Invidia TBE with resonator.
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Old 11-22-2007, 06:11 PM   #6
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Don't run ignition cut. Unless you want split shims and burned valves. Unless you want to rebuild your engine soon.
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Old 11-22-2007, 10:02 PM   #7
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From your other thread in PPB, your high 60 ft time is a result of wheel spin. You need to lower your LC and leave it on fuel cut in my opinion.
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Old 11-23-2007, 05:31 PM   #8
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Quote:
Originally Posted by Gethin View Post
Don't run ignition cut. Unless you want split shims and burned valves. Unless you want to rebuild your engine soon.
don't forget bore wash!
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Old 11-23-2007, 05:49 PM   #9
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Okay, okay, so no ignition cut unless I'm running nitrous. Got it. What about meth / alky?

Does not using ignition cut hold true while using C16 as well?
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Old 11-24-2007, 02:39 AM   #10
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I always use ign cut. No problems so far (where did I put that piece of wood????)

But I almost never use it anyway. I only recently started REALLY playing with it and really am only using flat foot shifting.
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Old 11-24-2007, 10:19 AM   #11
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Quote:
Originally Posted by SloRice View Post
If you aren't using nitrous, you fuel cut. It's not as harsh on the engine, header, turbo, etc as you aren't dumping all the unburnt fuel into the exhaust.

If you are using nitrous, you need to use ignition cut. Think about running nitrous...you need to add fuel with it or things go boom! Now think about using fuel cut with nitrous....
This is also the same for alky injection. If you shut down injectors while the alky is spraying your going to have a big problem.
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Old 11-24-2007, 10:36 AM   #12
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^ Hmm now you have me scared, I have my smc alky set to start spraying around 14psi and max 24psi, and hold about 14psi between shifts with injector cut LC/FFS.

What kind of wear/damage can be expected with long-term use of ignition-cut launch control when using "built heads" ? Besides blowing out exhaust gaskets, egt probes, etc.

I have sti heads w/shimless buckets, oversize supertech ss valves, supertech dual springs, ti retainers, etc etc.
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Old 11-24-2007, 11:23 AM   #13
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Originally Posted by jabbott View Post
This is also the same for alky injection. If you shut down injectors while the alky is spraying your going to have a big problem.
it's not nearly as bad as it is with nitrous, particularly "wet" nitrous.
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Old 11-24-2007, 08:12 PM   #14
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it's not nearly as bad as it is with nitrous, particularly "wet" nitrous.
yes but it causes the same problem. Instead of shutting down the cylinder it causes a severe lean condition, because the cylinder is running on just the alky being sprayed into it.
Lets say at wot the alky is equal to 30% of your fuel. Turn the injector off and thats equal to a non alky engine turing the injectors down 70%. Lean condition would be an understatement.
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Old 11-25-2007, 06:56 AM   #15
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yes but it causes the same problem. Instead of shutting down the cylinder it causes a severe lean condition, because the cylinder is running on just the alky being sprayed into it.
Lets say at wot the alky is equal to 30% of your fuel. Turn the injector off and thats equal to a non alky engine turing the injectors down 70%. Lean condition would be an understatement.
keep in mind there's "lean," which is volatile, runs hot and is prone to detting, and "lean" which will not combust at all.

by the time you inject 30% alchy:fuel ratio you'd better know what you're doing--typical targets are half that much.
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Old 11-25-2007, 07:09 AM   #16
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ignition cut is actually safer in the long term for your engine.

When you use a fuel cut limiter, you can run into lean conditions which can cause detonation and damage your engine as a result (bearings and piston rings mostly).

With an ignition cut, the most that can happen is your car runs a little richer if you hit the limiter.

Lastly, regardless of the way you implement your rev limiter, it is best not to hit it for sustained periods.

P.S. Just because an igbnition cut rev limiter is easier on your engine, doesn't mean it is good to sit on the limiter. The extra fuel will ignite in the exhaust and can cause undue stress of your turbo and lead to premature failure.
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Old 11-25-2007, 11:47 AM   #17
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I use ignition cut, I just didnt like knowing i was spooling the turbo and also cutting fuel. Injection cut is much smoother sounding, but Ignition cut blows flames out of my exhaust
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Old 11-25-2007, 12:36 PM   #18
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Looks like we may have a good debate here.
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Old 11-25-2007, 01:23 PM   #19
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Originally Posted by wrxsti.l View Post
ignition cut is actually safer in the long term for your engine.

When you use a fuel cut limiter, you can run into lean conditions which can cause detonation and damage your engine as a result (bearings and piston rings mostly).
i totally disagree.

this is an unfortunately common misconception about fuel cut.

first of all, injectors are either ON or OFF. there is no "medium."

if you can explain to me how an injector which is completely turned OFF for a combustion event can cause a lean mixture in the chamber, i'll be very impressed. (a mixture without fuel is not a "lean mixture" in my book--it's called AIR and it has infinite octane.)

note that i am NOT talking about what you may READ on a wideband o2 sensor, which not only has its own latency issues, but is also way downstream from the chamber itself--i'm talking about putting anything remotely close to a combustible charge in the chamber.

the only fuel you're going to see in a cylinder with zero pulse width on the injector is that which is wetting the walls of the head intake passages and intake valve. with air rushing past it at hundreds of mph, how much do you think is left behind there? how does that compare to the maximum combustible gasoline AFR?

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With an ignition cut, the most that can happen is your car runs a little richer if you hit the limiter.
no. as explained elsewhere, with ign cut, you have a perfectly combustible air fuel mixture IN the chamber (which will wet the cylinder walls with raw fuel), then in the 1000*F exhaust manifold a few milliseconds later. sooner or later you WILL get a HUGE afterfire which CAN and HAS lifted exhaust valves off their lifters. compared to the valvetrain, the turbo is the LEAST of your worries.

look around this site for people who did massive and catastrophic top end damage after the utec's launch control was released. pay particular attention to the mode of limiting. you WILL see a pattern emerge. what made matters much worse for many of them was the very delicate shim over bucket design in the 02 and early 03 model years, but make no mistake valvetrain damage can happen to ANY car with huge afterfires in the exhaust manifold. obviously high tension springs, and shim under bucket (or better still, shimless buckets) will reduce your risk, but it can never be eliminated.

also, if you have any cats in your car and you're dumping raw fuel into them, don't expect them to last. there's a reason why oem ecus are so sensitive to misfires, and it's the same reason why you'll never see an ign cut rev limit on any USDM production car built in the last 10+ years. too much raw fuel will destroy the catalytic reaction and possibly MELT the cat substrate itself.

Quote:
Lastly, regardless of the way you implement your rev limiter, it is best not to hit it for sustained periods.

P.S. Just because an igbnition cut rev limiter is easier on your engine, doesn't mean it is good to sit on the limiter. The extra fuel will ignite in the exhaust and can cause undue stress of your turbo and lead to premature failure.
i'm curious what the reasons for any revlimiting being "bad" (besides turbo wear, which is a non-issue with fuel cut) are?
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Old 11-25-2007, 07:00 PM   #20
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So ok, being mostly a lanuch control n00b Can I get some clarification



Ignition cut=flames out the tailpipe and loud cracking sounds and bad for engine or top end. Dangerous in particular to the valvetrain.

Fuel cut= less harsh sounding out tail pipe and not as bad for engine (not bad at all?)

Ignition cut=builds more boost
Fuel cut=builds less boost


Can you guys clarify if all of the above is true? If not, what part isnt?


And my next question

Would ignition cut ONLY for flat foot shifting (which I would think would be a LOT shorter duration) be as dangerous as using it for launch control?
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Old 11-25-2007, 09:13 PM   #21
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I'm not sure about the sounds. I run a mix with the Hydra. 95% fuel cut and 10% ignition cut.

I make about 10psi at the line with my 35R, but I try to not stay on the LC very long. So it would probably be more if I was on it longer.

As for having different cuts for LC and FFS, I don't know of any EM that can do that. UTEC and Hydra can't for sure.
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Old 11-26-2007, 07:29 AM   #22
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Ignition cut is going to sound a lot sloppier and loud than fuel cut, because there is going to be fuel detonating and backfiring.
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Old 11-26-2007, 10:23 AM   #23
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The ricer in me wants the "CRACK CRACK CRACK" with the foot and a half flames (not big fireballs, more like the mini torch) as it cracks when I shift or launch.

HOWEVER I dont think I will be using this on launch as I am on the stock gearbox. Just for FFS I think. I think I will be setting LC for like 7100rpm (my redline anyway) and I currently have FFS set for 5500 (I shift just before redline). I may be part time ricer but I am not going to put my engine in a big risk situation to satisfy that idiotic side of myself. A little risk, sure, lets do it But not big risk, and it sounds like anything more than a split second shift of ign cut is big risk.

But I also dont want to rebuild my valvetrain yet. I need the money for the PPG gears first. Then like a year later when I do the motor I am going to do a long block with P&Pd heads (possibly cosworth or EJ207 heads with the bore matched, like TOMEI did in that recent magazine article, I need to research the best options), cams and upgraded valvetrain, so ing cut should be safe (safer anyway) at that point.

Last edited by Defiant Autospeed; 11-26-2007 at 10:55 AM.
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Old 11-28-2007, 01:46 AM   #24
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Injector cut used here - builds about 9 psi after 1 sec on launch control:
http://www.youtube.com/watch?v=K-D_xjkUQpg
http://www.youtube.com/watch?v=nU6PCMoJu0I

Stick with injector cut - it builds enough boost to get you going without potentially harming your car. I'd love to shoot flames too, but meh... not worth the pain.

Also, if you want to get down the 1/4 a bit quicker, set your flat shifting to 6000 to 6600. I've been playing around with raising my FFS to 7600 (ej207). The car just launches after shifts now since the revs bounce at 7600 while I'm completing the shift - similar to power shifting. The vids above had the FFS too low and one can see the slight delay before the acceleration resumes after shifting.
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Old 11-28-2007, 09:44 AM   #25
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Is there something different with the gearing on that JDM transmission, I am hitting 1.80 60fts with no launch control
12.4@114 is awesome.

I think I should just upgrade my valvetrain and call it a day (I wish I could. Someday. Gearbox first though.)
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