Spark cut instead of fuel cut?

Apollo8642 · Post by **Apollo8642** » Thu Jul 21, 2011 9:48 am

Is there a possible way to cut spark instead of fuel at rev limit threw Nistune?

Another thing would it be possible to convert maf to map sensor some how threw Nistune?

thanks

Matt · Post by **Matt** » Thu Jul 21, 2011 12:48 pm

No for both. This is standard Nissan functionality and Nistune provides the mechanism to remap but unless there was some major code rewriting inside the Nissan ECU for both features its not possible at this stage

Apollo8642 · Post by **Apollo8642** » Thu Jul 21, 2011 1:22 pm

Thanks Matt

Apollo8642 · Post by **Apollo8642** » Fri Jul 22, 2011 6:19 am

is any one using any type of fuel cut defender out there?

s200rat · Post by **s200rat** » Fri Jul 22, 2011 6:57 pm

you dont need a fuel cut defender, nistune can be used to remove and set new fuel cut limits

Apollo8642 · Post by **Apollo8642** » Sat Jul 23, 2011 3:26 am

Well that's the issue I would like to cut spark not the fuel, having a turbo. I was hoping matt could make that some sort of an option in the future.

Fusion Ed · Post by **Fusion Ed** » Sun Jul 24, 2011 6:54 am

Then fit something like a Bee-R rev limiter, and set it lower than the ECU rev limit.

skyline_stu · Post by **skyline_stu** » Tue Aug 23, 2011 3:48 pm

Why are people SO badly wanting spark cut ???

Don't you realize that it can cause -

1. Cat Converter damage
2. Turbocharger damage from backfiring
3. Excessive emmisions

In 20+yrs tuning, I've NEVER seen an OEM system use spark cut limiting on a turbo car - with almost none using it on NA vehicles..(we're not talking about centrifigal rotor buttons here)
Keep with the fuel cut limiting and be happy knowing your engine [and turbo] should live a long and safe life !!

Stu

Apollo8642 · Post by **Apollo8642** » Wed Aug 24, 2011 3:29 am

I've seen both sides of the talk, fuel cut or spark cut. For the daily driver low boost fuel cut maybe okay for a motor that is pushing the edge of it's stock built performance levels, but once you have a built motor that is pushing over double or more of what it was ment to do stock then that's where things can change. Your now dealing with more heat and changes in the motor that you don't see in the stock system.

The thing that fuel cut can cause is detonation, and some times pre ignition, depending on what environment you have your car in, and I have seen melted, and damaged pistons from a fuel cut problems, and logs to back it up from a friends 2jz. Love seeing those sparkling spark plugs.

One, who runs a cat racing on a track, hell I don't run one at all for matter.
Two, if you think your damaging a turbo cause your back firing you have bigger issues and you better check your tune and build. I think it's more of an issue for ball bearing turbos then the journal type. Having a fuel cut defender that is ajustable is just important so your controlling how much fuel is being dumped, limiting back fires.
Three, really if your worried about emmisions then buy a Nissan Leaf, more power more gas, more emmisions, specially with the forced induction motors.

OEM turbo cars are built with safe guards in mind, and are made for a small window of performance, horse power and emmisions. Once you start changing those setting e.i. timing, fuel, igition ect. for more horse power you lose those oem factory safe guards your now taking the motor above and beyond what it was made to do from the factory. NA cars have the same setup but fuel cut won't hurt the NA motor.

skyline_stu · Post by **skyline_stu** » Wed Aug 24, 2011 1:51 pm

Here's a bit more detailed info for you to think about..

Is there a possible way to cut spark instead of fuel at rev limit threw Nistune?
Another thing would it be possible to convert maf to map sensor some how threw Nistune?
thanks

Cant see the mention of RACE cars in the original posting....

Apollo8642 wrote: The thing that fuel cut can cause is detonation, and some times pre ignition, depending on what environment you have your car in, and I have seen melted, and damaged pistons from a fuel cut problems, and logs to back it up from a friends 2jz. Love seeing those sparkling spark plugs.

Go ahead, please explain your theories behind this.. Just remember, we're talking about NISSAN's on this forum.. I'll bet money the 2J's running a cheap 'n nasty aftermarket system, with SOFT and HARD RPM limiting?? U gets what u pay for!! Many replacement ECU's do a pretty terrible job of soft RPM limiting. There needs to be cyclical rotation of cut cylinders if soft limiting is employed, with the correct RPM hysteresis employed. Something that EVERY CHEAP ECU DOES NOT DO... Over many years, I've fixed broken engines, turbo's and mufflers where the individuals didn't understand the configuration and limitations of thier system.

Spark cut doesn't work too well on vehicles employing a WASTE SPARK arrangements either.
I'll take you up on your offer and look at your 2J logs.

One, who runs a cat racing on a track, hell I don't run one at all for matter.

I do on my street and strip vehicles, so do all of my clients and many professional associates.. You should run a cat if your vehicle requires a one for road use. Doing this crazy stuff just makes it harder for all those out there wanting to do it right... It's the 0.5% that flaunt the rules and wreck it for the rest of the us trying to excell in our industry.

Two, if you think your damaging a turbo cause your back firing you have bigger issues and you better check your tune and build. I think it's more of an issue for ball bearing turbos then the journal type. Having a fuel cut defender that is ajustable is just important so your controlling how much fuel is being dumped, limiting back fires.

Please enlighten me about these 'bigger issues', I've worked in Turbo R&D. I'm failing to understand your point with ball vs bushed turbo's WRT spark cut rpm limiting.. If anything, the ball bearing core should handle it better, with the ability to deal with the increased thrust loading. Unburnt fuel, correctly mixed with air, often spontaneously ignites in the turbine housing/down pipe, or when spark comes on again, or if the parts are at the fuels' autoignition temperature.. This often causes extremely high load reverse rotation. This was a primary reason for turbo manufacturers to employ lefthand threads that tighten under reverse rotation. See the attached picture of a compressor wheel that experienced this EXACT mode of failure. I keep it to show people what spark cut REALLY does to your turbo. Fuel cut defender ??? WTF. Seriously, WTF!! These have no place or requirement on heavily MODIFIED vehicles, with aftermarket or factory management system.. Even on a factory ECU, when remapping, you should raise the boost or airflow cut, aleviating the need for a FCD. Matt mentioned this too. I'm somehow misssing the connection between FCD's and spark RPM limiting

OEM turbo cars are built with safe guards in mind, and are made for a small window of performance, horse power and emmisions. Once you start changing those setting e.i. timing, fuel, igition ect. for more horse power you lose those oem factory safe guards your now taking the motor above and beyond what it was made to do from the factory. NA cars have the same setup but fuel cut won't hurt the NA motor.

Just so you know, my Nistune Launch control system uses a fuel cut strategy! I'm yet to see any problems with damaged engines from a correctly employed fuel cut RPM limiter , even under boost. If you have ever configured antilag or launch control on any turbo car, you'd find that a spark cut prevents the antilag from operating as intended - it just backfires constantly. Launch control, on turbo cars, (with pump fuels) typically bog severly upon disengagement utilizing spark cutting methods. Most add on traction control systems cut out individual injectors (exactly like a fuel cut) to limit power.

** Note that Antilag and launch control are completly different beasts.**

Granted, a standard engine, powered up with add ons, does loose the safety margin. It becomes even more important to employ the correct techniques in an attempt to make your engine last.

FYI, changing from MAF to MAP is possible, but the gains don't outweigh the cost and technical difficulties involved. I'd rather a Mass Air system over a Speed density any day! Finer control, better repeatibility. The correct MAF doesn't limit power. You should go do some real world testing !! The calculated TP is NOT linear when referenced to rpm. JECS did this to make the maps more compact. Eg, A TP of 48 @2000rpm is not the same TP load as 48 @ 5000. Recoding every ECU's firmware would take forever to allow MAP sensing.

I'm not trying to turn this into a mine's bigger/better/faster pissing contest, just providing correct and factual information in an area where people just simply do not understand how and why it works.

So I'll say it again, "CORRECTLY CONFIGURED, A FUEL CUT RPM LIMIT, TURBO OR NA, WON'T HURT YOUR ENGINE. THIS IS WHY OEM's USE IT"

Stu Cornall

Apollo8642 · Post by **Apollo8642** » Tue Sep 13, 2011 8:48 am

You have some fair points. I've seen and heard about more engine damage from fuel starvation then back fires from the exhaust that hurt turbo's.

I would much rather replace a turbine wheel then a piston or two, hell ask a rotory guy what he's rather have fuel cut of spark cut that might also give you an answer. Again check your tunes if your having that issue.

Sorrry I don't have access to the maps for the 2jz I have a video of it running on the track

skyline_stu · Post by **skyline_stu** » Tue Sep 13, 2011 11:27 am

And I'll bet the Rotor's were using microtech's... They cut half the injectors off on their 1st step of rev limiting - which is a bad thing, the solution is only to use the hard cut (cuts all injectors) - but to be expected of those 'finest quality ecu's'.
They are that bad that there is no injector compensation table, we all(?) know what a problem the wrong latency causes !!!.

Latency should be ONE OF THE FIRST THING SET whenever tuning an EFI system.

I have never had a rotor fail with a MoTeC or Autronic ECU on limiter.

Apollo8642 · Post by **Apollo8642** » Tue Sep 13, 2011 12:16 pm

Anyways... with most of my friends that have drift cars we all spend a lot of time near red line and a lot of time hitting it. Leaning out a heavy boosted motor will do damage, hell if you lean out a NA motor to much you an do the same thing. If you have 20+ years tuning then you'd know that.

skylinegtrhr · Post by **skylinegtrhr** » Wed Sep 14, 2011 2:01 am

We have AE86 with S14 SR20DET drift spec (310 Wheel PS) for full two seasons and not one problem with Nissan OEM "fuel" rev limiter.

CoZZm0 · Post by **CoZZm0** » Wed Sep 14, 2011 5:49 pm

I've seen this point made all the time, fuel cut causes lean out causes motor damage etc etc... but how is it a lean out if there is no fuel to burn lean? No fuel, no bang. The AFR will always show lean on the limiter because for that cycle when fuel isn't injected, the motor becomes an air pump and nothing more right ?

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