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Old 05-06-2011, 03:14 PM   #1
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Default What kind of rev limiter should I be using?

The Megasquirt rev limiter settings have had me confused for a while, and I haven't been able to find a lot of beginner info on it. I'm looking for some help trying to pick which method of rev limiting makes sense for me setup, particularly if I end up trying the launch control or flat shift features later.

The car is a '95 with a DIYPNP running as a full standalone. MS2/Extra version 3.1.1 loaded at the moment. It's running the stock cat which I'm trying to keep working as long as possible (MD emissions testing with a tailpipe sniffer). The powertain is effectively stock (aside from the ECU). No turbo to worry about keeping spooled up.

If at all possible I'd like to keep the limiter as "soft" as possible so if I have a brainfart and hit it on a long stretch while autocrossing I don't unbalance the car too badly. I'd rather keep valves from floating if it comes down to it, though. It doesn't seem like flat shifting would be that useful, either if it couldn't keep the RPMs relatively steady.

All I can tell so far is that spark cuts seem like a really bad idea if you're running a cat, but I seem to have found some conflicting advice on that too. Should I be looking at a straight fuel cut, or would something else work better?
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Old 05-06-2011, 03:25 PM   #2
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I've been using straight fuel cut....hope someone chimes in regarding the fuel/spark combo cuts and if there's any reason to use that instead.
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Old 05-06-2011, 03:41 PM   #3
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to keep it soft use fuel only and be less aggressive with the "pull X from y events" and maybe less agressive with the spark reatard.

but it will make launch control weak, iirc.
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Old 05-06-2011, 03:53 PM   #4
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Originally Posted by Braineack View Post
to keep it soft use fuel only and be less aggressive with the "pull X from y events" and maybe less agressive with the spark reatard.

but it will make launch control weak, iirc.
If I do Fuel Cut only the cut X from Y event are greyed out. Are you saying to try Fuel&spark cut option but cut very few spark event?
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Old 05-06-2011, 03:55 PM   #5
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maybe. been a long time since I fooled with it.

but being able to change those values helps tune the speed/agressiveness in which the cut gives.

tuning the soft cut so it drops a crap ton of timing really helps you anticipate the hard limiter as well.
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Old 05-06-2011, 04:03 PM   #6
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Any idea how fine the line is between a less aggressive number of spark cuts and a cat-killing number of cuts is?
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Old 05-06-2011, 04:13 PM   #7
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if you do fuel and spark it shouldn't be a problem.
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Old 05-06-2011, 04:59 PM   #8
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OK, that kind of makes sense. If you do a spark cut only you're still dumping in fuel which screws up the cat. If you cut the fuel first it's OK to cut spark, though, since you've cut not only the fuel for combustion but the unburned fuel as well. Right?

So it's the Spark cut by itself that kills cats, not Fuel and spark cut.
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Old 05-06-2011, 05:01 PM   #9
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correct. if you cut spark, and keep fueling, once you spark agian, you shoot out flames.
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