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Old 03-22-2012, 02:14 AM   #1
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Default Spark Cut safe? The LIMITER THREAD

So I thought I'd start a spark cut thread, which could be an overall rev limiter / launch control / flat shift thread because searching here I didn't find near enough info and when turning to the famous google not much more came up.
I recently setup my launch control/flatshift and anyone who has a way to control fuel or spark probably has at least messed with their revlimiter.

After searching for quite a while, I couldn't find the real issues that come from spark cut. Obviously the more ignition events you cut the more explosions you'll get from the unburnt fuel which will destroy cats/mufflers *shrug* but could engine damage occur? Any proof of turbo destruction?

https://www.miataturbo.net/showthrea...launch+control ---Same question but I hoping to gain more specific info

https://www.miataturbo.net/showthrea...launch+control --- DXO posts about his turbine being destroyed and another due to spark cut, but both turbines happen to be 16g's, and my 2860rs has an inconel turbine wheel...

I'd hate to cut fuel(mostly pertaining to revlimiter), especially under boost because when running untimed batch, cutting fuel will certainly make it lean.

It really seems like the lesser of 2 evil's but it seems spark cut is safer if you're responsible with it (and not constantly shooting flames).

It also seems that explosions that powerful can't be good for "things"
How strong are factory exhaust valves? Stainless ones?

And anyone have insight as to durability of stronger wheels? Or weaker ones?

Lets hear your FACTS and opinions. But please no "I've been running ______ for _______ long and everything still works"
Thanks!!
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Old 03-29-2012, 10:45 PM   #2
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im interested in this too. i have mine to spark cut but im not running any cats so id imagine the pops im so fond of dont have enough resistance to do any damage.
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Old 03-29-2012, 11:38 PM   #3
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Its not the best idea in the world when you have a turbo.
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Old 03-30-2012, 01:20 AM   #4
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You are igniting fuel at your turbine wheel. Its bad for it.
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Old 03-16-2015, 06:01 PM   #5
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I couldn't find other topic for this but what would be safest way to run spark cut? I blew my old bp engine with over revs/pinging due to incorrect rev limiter settings.



Does these settings apply first fuel cut and then spark cut? And how many sparks will it cut (4 out of 5, 7 out of 9 etc) ?
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Old 03-16-2015, 06:18 PM   #6
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FWIW, I've always done a fuel cut with a 200 RPM window. No spark cut at all. No idea if that's good or bad, but it's what I've always done and it's worked for me.
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Old 03-16-2015, 06:55 PM   #7
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i had spark cut only on my rev limiter. for beak in reasons i had the rpm set at 4000rpm. it sounded like the world exploded. BAG BAG
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Old 03-16-2015, 07:27 PM   #8
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Quote:
Originally Posted by hustler View Post
Its not the best idea in the world when you have a turbo.
Quote:
Originally Posted by Bryce View Post
You are igniting fuel at your turbine wheel. Its bad for it.
Yes but how bad...are we looking at OEM expectations? Where it needs to last for 300k miles? Or are we talking 10-15 launches. Because I'm probably ok blowing up my $100 turbo if I get 3-4 years of spark cut launches.

I couldn't get fuel cut to sit at the same rpm the way spark cut does, but I also need to play with it some more.
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Old 03-16-2015, 07:38 PM   #9
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Quote:
Originally Posted by aidandj View Post
Yes but how bad...are we looking at OEM expectations? Where it needs to last for 300k miles? Or are we talking 10-15 launches. Because I'm probably ok blowing up my $100 turbo if I get 3-4 years of spark cut launches.

I couldn't get fuel cut to sit at the same rpm the way spark cut does, but I also need to play with it some more.
It's pretty hard on the turbo, even for a DIY only last a few years build. If you didn't set it up correctly, and gave me the car, I could blow the turbo with it in one night. It needs to be setup correctly (cuts JUST enough to spool the turbo, no more) and you only do it for 2-3 seconds before shutting it down. EGT's shoot through the moon with launch control enabled.

I had it on my car when I was N/A. I purposly removed it before I put the turbo on so I wouldn't be tempted to use it. There aren't many things I would purposely do to slow down my turbo miata, but I did that cause I knew it would shorten the life of my turbo.
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Old 03-16-2015, 07:41 PM   #10
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Interesting. What things do you have to setup? How much to retard?

When I used fuel cut last it would surge and fluctuate like 200-300 rpms. With spark cut it just sits on the limiter.
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Old 03-16-2015, 07:44 PM   #11
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I'm no expert, but you can change how many sparks it cuts, and at what RPM, and the retard amount, and mix that in with a fuel cut too.

I was talking about launch control BTW.

For a rev limiter, why NOT do a fuel cut? Who cares if it moves around a bit? If you want it to bounce less, change the "200" to 100 or something.
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Old 03-16-2015, 07:46 PM   #12
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I'm talking about launch control too. My bad. Using MS3 I only see options for changing to spark cut, nothing about how many sparks etc. I did change it to 100 but its more of a slow up and down surge, not just sitting there. I'll take some video later if I can.
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Old 03-17-2015, 12:21 PM   #13
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Old thread is old, but subbed anyway for good discussion. I don't want my turbine wheel to fall off
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Old 03-17-2015, 12:22 PM   #14
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Haha I didn't even look at the first post date.
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Old 03-17-2015, 12:25 PM   #15
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Quote:
Originally Posted by sasu` View Post
I couldn't find other topic for this but what would be safest way to run spark cut? I blew my old bp engine with over revs/pinging due to incorrect rev limiter settings.

Does these settings apply first fuel cut and then spark cut? And how many sparks will it cut (4 out of 5, 7 out of 9 etc) ?
it's cutting both fuel and spark, and you dont have progressive turned on.


this is how I saw progressive work last I fooled with it on the bench (ms2):

Let's say the hysteresis is 1000 rpm and hard is 7300.

So at 6300RPM it drops cly 1, then at 6500 it drops cly 3, then at 7000 it drops cly 4, then at 7300 (hard) it drops the last: cly 2.

Last edited by Braineack; 03-17-2015 at 12:53 PM.
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Old 03-18-2015, 04:12 AM   #16
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Quote:
Originally Posted by aidandj View Post
I'm talking about launch control too. My bad. Using MS3 I only see options for changing to spark cut, nothing about how many sparks etc. I did change it to 100 but its more of a slow up and down surge, not just sitting there. I'll take some video later if I can.
Yes fuel cut is going to go up and down for it to work. It has to shut the fuel OFF. Spark cut is smoother, but hell on turbo. Racecar, spark cut. DD, nope!
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