Bit of a thread dig but still relevant, has anyone played with the timing retard aspect of the launch control? I've had a fiddle with the rev limiter part but am thinking I might be able to build a small amount of boost (3-5 PSI or so) by fiddling with the ignition timing part. Anyone done it with any success?
Its a bit of a misnomer, Launch Control. It will work on any engine but a simple clutch switched rev limiter will achieve that. The limiter only engages with a clutch switch, AND the car below a set speed threshold otherwise launch will invoke any time the clutch is down and result in stalls. This is good for NA launching as it takes the time delay away from the throttle foot and the possibility of clutching it in between that silly practice of "blipping" the throttle and stalling. The same feature is modified for flat shifting when a full ignition cut is invoked ABOVE a specified road speed and rpm threshold. Anti-lag is the cool feature you hear on so many WRC rally cars to keep the turbo spooled as long as possible on throttle off/overrun with plenty of banging, farting and flames. Its a very easy feature to invoke but requires Fly-By-Wire throttle arrangement to work as bucketloads of throttle need to be fed to the engine while the fuel is increased and the timing is grossly retarded. Anti-lag is also a part of launching where you just mash the throttle and the ECU will grossly retard ignition timing and increase fuel delivery which skyrockets EGT's but spools the turbo nicely and rpm is set by soft cutting ignition all while stationary. A reasonably useless feature on a potent turbo car as once the clutch is lifted, full engine torque is available and so instant wheelspin and necessary sudden off-throttle, needed to control wheelspin/engine speed, and therefore boost loss is the result. Youd be quicker to control a launch with clutch slip. The final outcome that actually works is launch control, anti-lag, flat shift and traction control all integrated which "if" you get it right, will result in unbeatable launches which are usually repeatable. HOWEVER, different ECU's employ different coding strategies and even F1 and WRC teams dont get it right. Witness the number of WRC cars that stall on launch! TC is notoriously difficult to programme when integrated with launch control.
Why do you need to retard timing? I have traction control, with full throttle shift in the Z. It has two settings for driving on wet or dry roads. The launch RPM can be set at whatever RPM you want & is adjustable. The RPM for full throttle shift can be set at whatever RPM you want as well & is also adjustable. The amount of 'slip' which means wheel spin, can be set anywhere from 0% (no wheel spin), up to 20% & is adjustable in 1% steps. This great where you can stand on the pedal halfway through a turn & have a fair idea how far the rear end will step out. None of this is controlled by ignition cut.
Fuel cut onstranly is a very agricultural and potentially damaging strategy for power cut. Especially in turbocharged engines, due to residual fuel on port walls (wall wetting (xTau)) being pulled into the cylinders during engine periods AFTER fuel cut can result in dangerous enleanment detonations that you will never know is happening. Not to mention loss of boost and violent re-application of power over the hysteresis of the fuel or ignition only cutting strategy that actually extends the loss of traction event beyond what it otherwise would have been. The kind of timing retard Im speaking of is in the magnitude of approaching 90Deg atdc that requires a decent processor to achieve. In concert with a progressive fuel AND ignition cut results in a seamless and progressive loss in power and reapplication with minimal cut in boost. Not just a sucession of sudden engine cut and full power re-application of power over a specified hysteresis which in the TC world is equivalent to "limiter bashing" at traffic light derbies. So its kind of fun for a while but if you actually want to achieve some more positive that just a simple "too much right foot" aid to help prevent you looping it on a slippery corner exit, then you need to progress to something far more sophisticated than a plain fuel only power cut. If you are invoking TC and other engine power cut functions as a method of increased performance, a plain power cut is seriously lacking and can and does result in engine damage!
There is nothing agricultural about this traction control system. The system works by monitoring the speed of all four wheels using the ABS system. When wheel spin is detected the engine power is reduced, by cutting a single injector pulse, until grip is resumed. This occurs in a thousandth of a second, and appears to the driver as a slight misfire with no loss in acceleration. Maximum acceleration is achieved by limiting the slip between the tyre and the road. The point at which a tyre is just beginning to slip against the road gives the maximum coefficient of friction value. The idea of cutting fuel to an engine sets alarm bells ringing in engine builders, as they all know that running a lean combustion mode will elevate in-cylinder temperatures very rapidly. The denser the air/fuel charge, the more heat the lean burn can generate. Therefore it is vital that a fuel cut system will not cause a lean burn. Traction Control prevents lean burn by removing 100% of the pulsed fuel delivery – essentially the affected cylinder takes a gulp of fresh air; the in-cylinder temperature remains virtually unaffected. Prolonged fuel cut on one particular cylinder would cause scavenging of the petrol lining the inlet tracts, and when the next full fuel pulse arrived, it would be partially reduced in quantity by the re-wetting of these tracts. Traction Control rotates cylinder cutting to prevent this situation from occurring.
I think you should read posts more thoroughly yourself with xTau. You may be slightly less so supportive of fuel only cut once you understant what its effects on fuel cutting are. I also "think" I know how a basic TC system works. Engine damage is a REAL issue. There isnt any intelligent tuner that would invoke fuel only fuel cut strategy and keep a straight face. I use microsquirt on that bike in my sig and Adaptronic for everything else.
So trying to drag this back to 2 step rev limiters. I'm not talking about anti-lag or traction control. I was reading around the webs about people delaying the ignition timing slightly so that when the exhaust valve opens there's still pressure in the cylinder which then enables the turbo to spool up slightly under no engine load effectively giving you some positive boost on the line. Anyone done this or know someone who's step this up on their own Z? I'm trying to find some rough guidelines so I don't do my usual thing of completely fucking it up
Yes Racelogic traction control with full throttle shift & digital adjuster. Nissan ECU with NIStune. This system can operate using fuel or ignition cut.
Oopps! Pulling ignition out to reduce torque and spool a turbo free revving isnt just a "slightly" adjustment. Well not of you consider at least 60 degrees of retard or more is slight! You need to cut engine torque to the point that the vast majority of your heat energy just goes out the tailpipe, spooling the turbo and the engine just bumps on the limiter!!! I spent hours configuring launch control (NO TC) into a modest (140Kw) 1.5L turbo 4 and all I achieved was lots of boost at 3500rpm and once the clutch was hit, it just instantly limiter bashed until road speed equalled wheel speed @ target limit RPM, or I just lifted off and pedalled it the old fashioned way which kinda defeated the whole purpose of invoking launch control in the fist place!!!! Lower the target limited speed and when it hooked up, often boost was already lost and it just drove on as if youd just rolled onto the throttle at that low speed and once spooled, fried tyres again! I was actually far faster lifting off with launch control disabled. I sold the car before i bothered to fit my wheel speed sensors and invoke a proper launch/TC scheme!! As I mentioned, ts a very tricky thing to get right and even at the highest level of motorsport, they dont often get it "just right"
Tbh it wasn't all that great apart from w*nk factor. The feature pack made tuning a lot easier though.
