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ALS Anti-Lag on LINK ECUs

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Hi guys, I have quite some experience setting up anti-lag for rally cars but usually on GEMS/Simtek (I believe GEMS also designed AEM).

With the GEMS you have the option of any combination of Fuel Limit (skipping fuel injection events) and Spark Limit (as well as obviously ignition retatd) as a means to reduce torque with als on or off when running a jacked open throttle.

I believe Motec used to force you choose whether to use fuel limit OR spark limit as did Pectel.

Usually fuel limit alone is fine and I consider spark limit a 'last resort' to prevent push on when running a lot of JOT.

The LINK however seems to only have the option of spark limit. The beauty of fuel limit is you can control heat (both of the exhaust valves and of the manifold/turbo). With only using retard and spark cut you're forcing the engine to burn all of the fuel with no 'fresh air' mixed in (as would be the case using fuel limit) and by spark cutting you're forcing the combustion into the exhaust manifold with isn't great for the valvetrain if you're using bucket and shim.

Please can someone explain the thought process behind only offering spark cut for ALS and how to control heat with large JOT to get effective ALS on LINK without burning up the turbo.

Cheers.

I dont have a huge catalog of experience with ALS, only done a couple of club level rally cars but never had any trouble achieving the required antilag effect and no difficulty controlling heat. Just the fuel trim and cut table seemed to give me enough adjustability. The cyclic idle is done with fuel cut for obvious reasons.

The only reason we dont have fuel cut as an option for the ALS is that until now no one has asked for it as far as I know. I didnt even think it would be effective.

Im not sure if Im understanding what you are saying fully - but whether you cut fuel or ign you've still got the same amount of "fresh air" passing through. Just with fuel cut you will have less fuel in the manifold to burn. So wouldnt just putting -ve numbers in the antilag fuel trim table have the same net effect?

I suspect if you really want some fuel cut with antilag then you could use a virtual aux and a GP RPM limit table set to advanced mode to add a fixed % fuel cut when antilag is active.

I dont have a huge catalog of experience with ALS, only done a couple of club level rally cars but never had any trouble achieving the required antilag effect and no difficulty controlling heat. Just the fuel trim and cut table seemed to give me enough adjustability. The cyclic idle is done with fuel cut for obvious reasons.

I have never found a need to add additional fuel, having your fuelling come from the main fuel map with no additional enrichment has always worked just fine for me.

The only reason we dont have fuel cut as an option for the ALS is that until now no one has asked for it as far as I know. I didnt even think it would be effective.

Works fine. If I take all the fuel limit out and resume normal timing, my STi would idle at about 4000rpm (because of JOT). With ALS OFF I run no retard and as much as 80% fuel limit on the lowest TPS row (tapering as throttle is applied). I'm still a bit confused how LINK controls large JOT with ALS off but seems it's done automatically with the cyclic idle function (what's the difference between cyclic idle and cool down)? With ALS ON I have maybe still as much as 40% fuel limit on the lowest TPS row with a fair bit of ignition retard (values in the ignition retard maps are deducted from the main ignition map so a value of -40 in the ALS retard map might result in something like spark at 10 degrees ATDC depending on the value in your main map). I presume LINK works the same and that values in the ALS retard map must be preceded with a '-' minus? Few ECU companies seem to explain properly whether these values are ABSOLUTE or to be deducted from the main ignition map - Cosworth couldn't even tell me for Pectel so you're left to log it to figure out what it's actually doing.

Im not sure if Im understanding what you are saying fully - but whether you cut fuel or ign you've still got the same amount of "fresh air" passing through. Just with fuel cut you will have less fuel in the manifold to burn. So wouldnt just putting -ve numbers in the antilag fuel trim table have the same net effect?

Ah, perhaps. Like I said, I've never played with the fuelling enrichment with ALS on as from the way of working I'm used to (fuel cut) then taking fuel out by VE trim would result in a lean condition of those fuel injection events with are lit up in the cylinder. You are of course right that pulling fuel out will result in less fuel in the manifold from those cylinders which are NOT fired but what of those cylinders which ARE fired, would the leaner mixture still apply to them? Also, as I said, my aim is to control heat (both of the exhaust valves and of the manifold/turbo). Spark cut may help the valves themselves but it sure isn't helping the manifold and turbine; the aggressive explosions caused by spark cut gives the turbine a sudden kick which can snap the shaft and can lift valves and throw shims.

I suspect if you really want some fuel cut with antilag then you could use a virtual aux and a GP RPM limit table set to advanced mode to add a fixed % fuel cut when antilag is active

Sounds complicated I don't know how you'd begin to set an rpm limit which works works at all engine speeds - sounds like a contradiction in terms.

This is a very old statement from Pat Herborn (of Syvecs):

Now let's consider the car going down a stage, with ALS on. We now want a completely different operation when the throttle is "shut". We want the turbo to make boost, so we have to drive the turbine, and for that we need exhaust gas. Lots of it, and preferably hot. Logically, then, one could just use an ignition cut, so the fuel lights up in the manifold, but then it won't be long until the turbine turns into a molten lump of metal. You can't run the ALS like this without fragging something so we need to try to maintain the drive to the turbine without melting it, so we need less heat, but if we lose heat then the energy available to the turbine per unit mass exhaust gas also goes down. Solution is to increase the mass of exhaust gas available, so you have the same energy, but less heat. You could now run ignition retard instead of cut; the engine absorbs some of the heat (mostly in the exhaust valves, which get a right bashing). We still have a problem; now the turbine is relatively happy but the exhaust valves are not. We need even less heat, but at the same time we don't want to lose energy. So we jack the throttle further, increasing the mass flow further, so we can have less heat per unit mass, but just flow more mass. We can keep the heat down by simply forgetting to inject fuel. If there's no fuel there it cannot create heat. So we need a fuel cut table.

It sounds to me like cyclic idle does exactly what you are asking for. It will apply an adaptive fuel cut to achieve whatever "idle speed" you want with the throttle jacked open (the target idle speed is the setting "cyclic idle limit").

"I presume LINK works the same and that values in the ALS retard map must be preceded with a '-' minus? Few ECU companies seem to explain properly whether these values are ABSOLUTE or to be deducted from the main ignition map - Cosworth couldn't even tell me for Pectel so you're left to log it to figure out what it's actually doing."

The numbers in the "retard table" will mean different things depending on what mode you set for the "AL Ign Retard Mode". If its set to "degrees", then it is "added to" the currently commanded ign timing (so a value of -10 in the table would retard the timing 10 deg off the main ignition table). If it is set to "degrees absolute" then it overrides everything. -ve numbers mean ATDC, +ve numbers mean BTDC in this mode, so if you had a value of -10 in the table your ign timing would be 10ATDC. Finally there is a "percent mode", where a percentage is added or subtracted for the commanded timing.

Note the help file explains all these settings and gives some example set-ups. If you click on any setting and hit F1 you will usually get enough info to understand how it works.

Here's the explanation of the retard mode:

And here is the explanation of how the number in the retard table work:

Thanks, for that explanation but still sounds as though cyclic idle is only active with ALS OFF, so still no fuel limit with ALS ON. I'd have to get a thermocouple in the up pipe and actually try it to see how much abuse it gives the turbine but I've had some bad experiences with spark cut which have put me off using it. I don't even like it for flatshift.

It's nice to have the options of absolute retard but not necessary IMO.

As you can probably tell, I haven't delved into it too deep on the LINK as I was put off by the lack of fuel limit and this was a customers car which is only used for track days and he just wanted it setting up for the noise as much as anything so I only opened the idle speed control valve with ALS on and didn't jack the throttle a lot in the end.