# Link G4 Worthwhile?



## sh3lldon (Nov 11, 2017)

I am considering purchasing a Link G4 for my R33 GTR

Currently the car is standard except for HKS Sports Cat and Tomei TI Expreme Cat back, I do intend to modify further in the future so the Link would be required at some stage

as a note I am not expecting for it to increase my power by masses on a standard car just to refine what is there and map for our fuel etc

Being new to Nissans I have a couple of questions

- is it worthwhile addition on essentially a standard car at this time

- Who is recommended to fit and map the Link system? I am based in central scotland but have no issues travelling south to get it done

- If it is something I go for are there any other additions that are worthwhile being done at the same time?

Thanks in advance


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## CRDR32 (Oct 22, 2017)

For what its worth, I'm getting a Link fitted next year (due to budgets). A good friend has one fitted to his RX7 and the functionality is really impressive. Its also very user friendly and with the data logging features you can constantly refine your map. The more you drive it, the better it gets! There is also a very help forum for the Link community as well. 
When I do get mine I'm also going to pull the CAS out of my engine and install a trigger kit from NZ Wiring. Something that my current 'chipped' (old tech) ECU won't accept.
I've heard good things about Haltech also, but I have seen the Link stuff in action. There's probably not much between them tbh


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## sh3lldon (Nov 11, 2017)

Thanks hopefully some info from owners currently running it


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## joshuaho96 (Jul 14, 2016)

The Link ECU doesn't work with the stock twin MAF system. If you want to keep the MAFs for driveability reasons get a Haltech Elite.

If you want to keep ITBs don't get rid of the MAFs. It takes a ton of work to get speed density working right with ITBs.


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## AlexJ (Apr 3, 2003)

sh3lldon said:


> Being new to Nissans I have a couple of questions
> 
> - is it worthwhile addition on essentially a standard car at this time
> 
> ...


just for clarity the g4 is the previous generation link ecu, the current pnp model is the g4+ which added some important stuff.

is it worth it on a stock car? no, a chip tune is plenty imo.

if you want a g4+ anyway then look at rod bell, mgt or abbey (in order of distance from you)

if you do go for it then add a canbus lambda sensor, oil pressure protection, boost control (open loop).

Most aftermarket ecu's dont support MAFs. Not a huge issue imo. Someone who knows rb26s and the link ecu will know how to map it so that the ITBs are not an issue. Essentially you map fuelling against throttle (like n/a ITB cars) and lambda target and ignition timing against MAP.


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## joshuaho96 (Jul 14, 2016)

I'm not really a fan of using TPS as a load signal, really only works at WOT or some variant thereof. MAP + TPS blending is rare as an OEM solution for a reason, the only car I can think of with ITBs and no MAF is the 4AGE 20V Blacktop.

Modern MAF sensors can be really, really good. They can even sense reversion in the latest hot film sensors like the ones in the R35, although it's up to the ECU to make sense of the signal. If you're not after a big power build it's better to just take some of the restriction and keep the MAFs. MAP sensor is still valuable data for the ECU for boost control and transient response but there is really no world in which TPS is the ideal load sensor.


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## sh3lldon (Nov 11, 2017)

thanks for the info guys some food for thought.


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## FRRACER (Jun 23, 2013)

Link suffers more from timing scatter than a Haltech something to consider. As a result you are advised to get a aem trigger disc or one of the tuners will offer a trigger kit.


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## CRDR32 (Oct 22, 2017)

FRRACER said:


> Link suffers more from timing scatter than a Haltech something to consider. As a result you are advised to get a aem trigger disc or one of the tuners will offer a trigger kit.


This is what I'm going to do when I get my ECU. When you consider the outlay of getting a new ECU, the wiring, the new plus additional sensors and then dyno time, you're daft not to while you're in there and its in bits.


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## joshuaho96 (Jul 14, 2016)

CRDR32 said:


> This is what I'm going to do when I get my ECU. When you consider the outlay of getting a new ECU, the wiring, the new plus additional sensors and then dyno time, you're daft not to while you're in there and its in bits.


If your rev limit never exceeds 8000 RPM timing scatter is irrelevant with a good CAS + an ECU that is designed to read it properly. If you plan on going further then yes a trigger kit makes sense but most ECUs these days are plug and play, only thing you need to run is a MAP sensor.


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## Manzgtr (Jan 11, 2012)

buy it


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## CRDR32 (Oct 22, 2017)

joshuaho96 said:


> If your rev limit never exceeds 8000 RPM timing scatter is irrelevant with a good CAS + an ECU that is designed to read it properly. If you plan on going further then yes a trigger kit makes sense but most ECUs these days are plug and play, only thing you need to run is a MAP sensor.


I've got an ex-track car imported from the motherland. Its got a HKS chip upgraded ECU and the HKS VPC. The MAF's are long gone and the turbos have been replaced by two big laggy SOB's. Its ported to within an inch of its life, has cams and 750cc injectors. Its also meant to have been bored and stroked, but I wont know that until I pull the engine next winter to see what I've actually bought!! Plus a lot of CAS units on these cars are now 20yrs old, they will inevitably start to fail, so instead of buying a brand new one for £300+ I'm going trigger kit personally, when the time comes.
From what I can see its all been properly done, its just old tech. Its been tracked, so if it was going to poo itself, it would've done it by now. 
But, I don't like not knowing what the fueling is doing so a wideband is going in this weekend and also a 2nd hand newer CAS as shes a pain to start sometimes and she's been giving me other 'bad CAS' symptoms as well. Hence the need for some new technology on her, where I can wire in Oil & Water temp & pressure safety limits.
Other than that, when she does fire up and run, OH MY GOD...... One eye on the road, one eye on the revs, and the third tightly clenched!!!!


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## joshuaho96 (Jul 14, 2016)

If you have gigantic turbos you should be going with a single throttle body anyways, the ITBs become a restriction for big power builds. Then you can use pure speed density too.


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## FRRACER (Jun 23, 2013)

joshuaho96 said:


> If you have gigantic turbos you should be going with a single throttle body anyways, the ITBs become a restriction for big power builds. Then you can use pure speed density too.


Is ITB a restriction? 100mm vs 6x45 or enlarged 48mm?

https://youtu.be/uS3yHPfT9I8


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## joshuaho96 (Jul 14, 2016)

FRRACER said:


> Is ITB a restriction? 100mm vs 6x45 or enlarged 48mm?
> 
> https://youtu.be/uS3yHPfT9I8


I think as long as you're somewhere in the ballpark of what the RB26 was "intended" to run for power (~600-700 hp in race trim?) the ITBs are probably going to be better. But I imagine that eventually (like 1000 crank horsepower) you want to run a single throttle body as the throttle body itself becomes a noticeable restriction.


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## FRRACER (Jun 23, 2013)

joshuaho96 said:


> I think as long as you're somewhere in the ballpark of what the RB26 was "intended" to run for power (~600-700 hp in race trim?) the ITBs are probably going to be better. But I imagine that eventually (like 1000 crank horsepower) you want to run a single throttle body as the throttle body itself becomes a noticeable restriction.


Single throttle is easy to tune but that does not always mean it’s a better choice. STD ITB can be machined out to 48mm which again over 6 of them is plenty for even 1000/1200hp.


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## joshuaho96 (Jul 14, 2016)

I would wonder how you would actually make a big power engine run well in open-loop with ITBs. No MAF has enough range at the high end without major compromises at the low end. MAP sensors will tell you how much boost the plenum is seeing but I don't know how you'd measure the actual pressure of the air in the cylinder due to the "vacuum leak" that you would get from the other cylinders.

I suspect the only solution there is alpha-N at the high end with boost compensation using the MAP sensor.


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## AlexJ (Apr 3, 2003)

given that two z32 MAFs can read over 1000bhp with decent low end resolution - how much do you count as big power?


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## CRDR32 (Oct 22, 2017)

FRRACER said:


> Single throttle is easy to tune but that does not always mean it’s a better choice. STD ITB can be machined out to 48mm which again over 6 of them is plenty for even 1000/1200hp.


I've read that the drivability of high boost single throttle plates is pretty crap. Hence why Nissan spent a small fortune on refining a perfecting the 6 ITB's in order to get better response throughout the rev range. Anyway, each to their own, I'm happy with top mount twins and ITB's at the moment. All I'm after is 'grin factor' and she has it in spades at the moment!


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## joshuaho96 (Jul 14, 2016)

AlexJ said:


> given that two z32 MAFs can read over 1000bhp with decent low end resolution - how much do you count as big power?


My understanding was Z32 MAFs were good for about 800, not 1000. And if you're after some crazy 1000+hp 3.2L drag build you probably need some kind of PWM based MAF instead of voltage.

Obviously, the number of people that would actually build that kind of engine are few and far between but hey.

If it came down to personal choice I would probably say -9s and keep the MAFs with a Haltech but having a car that behaves well on the street is my primary concern so...


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## FRRACER (Jun 23, 2013)

Those 1980s mafs need to be scrspped. R35 style ones are the way forward same with injectors.


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## joshuaho96 (Jul 14, 2016)

Agreed, I'm just saying that I'd rather have MAF for a street car, especially to retain the ITBs.


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## mambastu (Feb 13, 2002)

I've recently moved to a G4+ and I would say that you need to budget for a crank trigger kit as part of the conversion due the rpm fluctuations. An AEM type CAS disk didn't help with mine. If you want to future proof then fit one but if you're not going nuts with power then a normal MAF Power FC is cheap and will do the job. A Power FC D-Jetro will be better with a single TB car.

A lot of balls about ITB's on this thread. The standard 45mm throttlebodies have a greater surface area than a single 100mm TB when fully open. The only reasons to change to a single TB are to get the best out of a D-Jetro, reduce weight or complexity or use a drive by wire throttle.


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## Timtrim (May 6, 2016)

Only herd good things


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## Lith (Oct 5, 2006)

mambastu said:


> you need to budget for a crank trigger kit as part of the conversion due the rpm fluctuations. An AEM type CAS disk didn't help with mine.


OP - ignore this. It sounds like Link brought this guys attention to a pre-existing mechanical problem and for some reason decided to blame the Link. It's a bit like a cancer patient telling you not to go to the Doctors because you end up with cancer.

You DO NOT need to go a crank trigger setup to get sensible triggering with a Link.


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## mambastu (Feb 13, 2002)

Lith said:


> OP - ignore this. It sounds like Link brought this guys attention to a pre-existing mechanical problem and for some reason decided to blame the Link. It's a bit like a cancer patient telling you not to go to the Doctors because you end up with cancer.
> 
> You DO NOT need to go a crank trigger setup to get sensible triggering with a Link.


This is a forum where people air their experiences. If it doesn't agree with your 'opinion' and you don't like it then feel free to head back to SAU where your objectionable way of posting might be more appreciated.

I have new cams (no end wear) and on the dyno Abbey tried my original CAS, my re-wheeled 24-1 CAS and their known good CAS. Cam belt re-tensioned a few times to see if it reduced the problem. The reality is that I have an up to 500rpm variation from 6800 upwards.I currently have a 6500rpm rev limit set while I sort out a crank trigger. 
I have no vested interest in damning the Link. I paid for it with my own money and I think its a really good Ecu with great features and PC-link is excellent but I can see the problem on my datalogs. Abbey had no vested interest in pushing for me to buy a trigger kit because they know I do most of my mechanical work and I bought the trigger kit from source.

I was aware of this going in to it as I research the hell out of everything so you should be aware of this potential issue as it may affect you. It certainly seems to affect a lot of other people and people that tune them are aware of the issue. 
If I fit the trigger kit and it doesn't resolve the issue I'll happily put up my hand and update this post.


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## Lith (Oct 5, 2006)

mambastu said:


> This is a forum where people air their experiences. If it doesn't agree with your 'opinion' and you don't like it then feel free to head back to SAU where your objectionable way of posting might be more appreciated.


Agreed, if it was presented your post as an opinion or some observations of behaviour I probably wouldn't have said much (if anything) but you stated it as though it's a fact... which I strongly disagree with.



> If I fit the trigger kit and it doesn't resolve the issue I'll happily put up my hand and update this post.


That's the trick here - and why I commented on the post. It WILL (well it should) fix the issue. That's because there is an issue with your triggering and it has nothing to do with what ECU you are running. You've told someone else they HAVE to buy a trigger kit because they have a Link because you had triggering issues, oh yeah and you also happen to have a Link.

They only need to fix their car's triggering if they have triggering issues, and that applies regardless of what ECU they have - if the triggering is inaccurate then the ECU cannot possibly have an accurate gauge of where the crank is at. A smooth rpm graph is more to do with data filtering than accuracy, smooth data doesn't mean accurate by any stretch.

Don't get confused about the point of my post - I'm not upset at all, I don't own Link nor have any interest in it, nor am I trying to defend stock CASs. This was nothing personally in regards to you, this was purely trying to put a stop to bad info propagating. I don't see any need in leaving because you don't like being corrected when you make incorrect statements.

For anyone who does have a mechanical triggering issue and can't justify a full crank trigger kit then these are a much more affordable and simple to implement solution (as long as your ECU has configurable triggering): https://www.nzwiring.com/index.php/services/custom-components/rb-cam-trigger-kits/


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## joshuaho96 (Jul 14, 2016)

If reducing the resolution of the CAS wheel manages to resolve a "noise" issue the problem is the ECU, not the CAS itself. I'm also not a fan of variable reluctance sensors, they tend to require more work from the ECU to interpret the data in the first place and are very sensitive to noise, most manufacturers recommended twisting the differential wires and shielding them with copper grounded to the chassis. Keep in mind that Nissan was not entirely stupid to use this optical system, the high resolution allowed for extremely fast engine start (this reduces emissions) and as long as the entire system is in good working condition you will have accurate cam-based ignition timing as the ECU knows what tooth to look for to trigger the coils.

Timing scatter otherwise is a function of timing belt stretch between the crank and cam leading to inaccurate crank signal. The only way to fix that is to read the signal at the crank. Everything else is just filtering the signal to make an educated guess as to what the engine is actually doing. If you really wanted to I'm sure you could actually guess to what extent inconsistent belt stretch is impacting the accuracy of the "crank" signal on the CAS, it's just not worthwhile to spend all of that time figuring it out when you could get a trigger kit and be done.


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## Lith (Oct 5, 2006)

joshuaho96 said:


> If reducing the resolution of the CAS wheel manages to resolve a "noise" issue the problem is the ECU, not the CAS itself.


Agreed, entirely. I'm not going to argue too hard on how much of an issue the Link has (or hasn't) with processing signals from a 360deg opto sensor as I don't have enough to say either way but realise there is always the possibility given how common the issues are. The discussion here however isn't really talking about that, I was simply debating the point that you HAVE to go to a crank setup with a Link... bearing in mind what has already been mentioned was someone having issues with the 24 tooth trigger disc.



> I'm also not a fan of variable reluctance sensors, they tend to require more work from the ECU to interpret the data in the first place and are very sensitive to noise, most manufacturers recommended twisting the differential wires and shielding them with copper grounded to the chassis. Keep in mind that Nissan was not entirely stupid to use this optical system


Yeah definitely a valid point, agreed. Would be nice to have an aftermarket opto trigger setup - maybe there is? 



> the high resolution allowed for extremely fast engine start (this reduces emissions) and as long as the entire system is in good working condition you will have accurate cam-based ignition timing as the ECU knows what tooth to look for to trigger the coils.


Agreed too, shifting a bit from the scope of this discussion - though I guess with a crank trigger setup you can still use the cam sensor to find which cylinder you are on. A lot of crank trigger setups only seem to use the cam angle sensor for #1 TDC sync, however.



> Timing scatter otherwise is a function of timing belt stretch between the crank and cam leading to inaccurate crank signal. The only way to fix that is to read the signal at the crank.


Timing scatter CAN be function of timing belt stretch but I suspect the vast majority of cases which are blamed on timing belt stretch are actually a result of the worn star socket setup which Nissans use to transfer drive from the cam to the trigger disc. That is why the NZWiring cam trigger solution works so well despite being still being a 24-tooth cam driven solution, as it does away with any of the Nissan's parts and just bolts directly to the cam wheel - eliminating any wear and chance of movement relative to the actual cam angle.



> Everything else is just filtering the signal to make an educated guess as to what the engine is actually doing.


Agreed. I don't know what Link does, and I don't know what other ECU manufacturers do but I do think there is a reasonable chance that some manufacturers may do heavy filtering of the crank trigger input when configured for a Nissan CAS. That does reduce the potential range of error from the signal but also reduces the accuracy of the signal, so on the off-chance there is no "play" in the cam belt or star socket that would cause erratic timing. They have basically done the equivalent of drastically reducing the tooth count in order to achieve a smoother signal, which will result in a smoother looking rpm log/power curve/drive etc but partly because the error is more consistent as opposed to non-existent. 

It seems the Links are probably a lot more trusting of the signal and that of course has obvious real world implications when the signal is erratic. It doesn't mean you will have issues unless there is any erratic signalling, and a crank trigger setup is not the only valid solution.



> If you really wanted to I'm sure you could actually guess to what extent inconsistent belt stretch is impacting the accuracy of the "crank" signal on the CAS, it's just not worthwhile to spend all of that time figuring it out when you could get a trigger kit and be done.


Refer to my comments above on what I suspect (and in every case I've had the chance to, proven) is the actual cause for a lot of RB timing scatter issues.


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## joshuaho96 (Jul 14, 2016)

Yeah, if there's slop between the CAS and the piece that drives it then that can be a problem too, but that's more a maintenance problem due to the sheer age of these engines as opposed to a design flaw. I'm sure that replacing the worn parts would fix the problem in that case just as well as using the NZ Wiring kit.


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## Sub Boy (Jan 28, 2008)

I also would like to point out, Haltechs, Motecs, EMUs all encounter the same issues with timing scatter via the factory CAS.....so don't anyone think it is only Link.
Can't say we have ever seen one however that didn't fix the issue with a 24+1 replacement CAS disk


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## joshuaho96 (Jul 14, 2016)

Do you have evidence of this? Posts like this suggest to me that some ECUs have more work done to them (filtering, plausibility checks, etc) to read the CAS properly than others: https://www.sau.com.au/forums/topic...n-rb2630/?page=3&tab=comments#comment-6366796

"I'm having this trigger issue at 5000rpm on my rb26 and need to get hold of a 24 slot trigger disc for my cas. I'm having the problem as im running a vipec v44 ecu. For people's information we tried haltech platinum series ecu and its able to read the signal no problems so its an ecu dependant problem"

7k cut off g4+ plug in, cas issues - G4+ - Link Engine Management

"r33 gtst series2 g4+ plug in cas issue I have a rb26 head on an rb25 we are trying to make snowy mountains 1000 next week

we cant rev it past 7000rpm there is timing scatter and JEM ingulburn pluged in a haltech and could rev it to 8500rpm no issues

how can I resolve this issue with the link g4+ plus plug in

we tried new cas ,new coil pack harness , more earth straps and still it got worse could there be a way to locate the issue"

I'm guessing that Link's ECU is more used to larger gaps between teeth so small inconsistencies in timing from tooth to tooth don't have big impacts on the calculated RPM. You could accomplish the same thing with a low pass filter applied to RPM.

As Lith has mentioned I suspect that part of the timing scatter problem is that the cam -> CAS drive mechanisms in most engines is starting to wear out. JWT makes a part specifically to help remedy this, mostly just because Nissan won't sell their part separately. Jim Wolf Technology website

Edit: I'm willing to bet that if you keep the CAS drive + CAS sensor working properly and you use an OEM or Nismo timing belt that you will never need a trigger kit for stock rev limit (8250 rpm fuel cut, should pull some timing after 8000 RPM to soften the cut). If you want to go over the stock rev limit then I would expect to need a trigger kit as the tolerance stack probably becomes too much to handle.


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## FRRACER (Jun 23, 2013)

joshuaho96 said:


> Do you have evidence of this? Posts like this suggest to me that some ECUs have more work done to them (filtering, plausibility checks, etc) to read the CAS properly than others: https://www.sau.com.au/forums/topic...n-rb2630/?page=3&tab=comments#comment-6366796
> 
> "I'm having this trigger issue at 5000rpm on my rb26 and need to get hold of a 24 slot trigger disc for my cas. I'm having the problem as im running a vipec v44 ecu. For people's information we tried haltech platinum series ecu and its able to read the signal no problems so its an ecu dependant problem"
> 
> ...



I have said this all along link is prone to having issues with timing scatter and having seen the words Link ECU and Trigget Kit I***8217;m the same sentance pushed out certainly by Uk tuners I decided to go towards a Haltech. I run an Elite with a new Nissan CAS. Rev limit 8700 rpm no issues. Adam at JEM is a good guy and knows his stuff you are in safe hands.


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## proline (Nov 21, 2002)

Is there a way to determine if there is likely to be an ignition scatter problem with the Link G4+ BEFORE fitting e.g. using timing light.


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## joshuaho96 (Jul 14, 2016)

proline said:


> Is there a way to determine if there is likely to be an ignition scatter problem with the Link G4+ BEFORE fitting e.g. using timing light.


Timing light won't help, that's one layer of abstraction up. If you're on the PowerFC or stock ECU or something like that you won't be able to see the actual signal.

There are a few ways I can think of to figure this out, depending on how sure you want to be. If you have an oscilloscope and you want to make a harness and you have a dyno (or the problem shows up just revving in idle) then you could measure the pulse train and do some math yourself to see the calculated RPM from sample to sample. I don't have the data to say what you should expect but with 2 degree resolution I would expect a good amount of noise. It would be interesting to see how closely Link G4+ measured RPM correlates with this raw RPM data.

Another option is to check the CAS drive as previously mentioned for free play, binding, etc... and the timing belt for proper origin and tension. Depending on what tools you have at hand and what you feel more comfortable doing one of these will probably be easier/faster/cheaper than the other.


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## proline (Nov 21, 2002)

Ok - thanks for that - looks like it will be the second option. Does ensuring everything is mechanically sound guarantee that there will be no ignition scatter issues or can that only be achieved by installing crank trigger / NZ Wiring options? I am trying to avoid problems with the dyno session after the initial install. 

The tuner will not be installing the Link. Would it be possible to test for scatter after the initial install with the car running on more or less a base map. Obviously this wouldn't be an option if the car needed to be under load but I'm not clear if it would be possible to detect the problem otherwise?


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## Lith (Oct 5, 2006)

The Link actually records a trigger warning if it believes there is an issue, though it has to be pretty bad to reach that point. The rpm logging can be pretty erratic as you pull through the rpm if there is a problem, as well. Realistically the most accurate way is by having a crank trigger setup as well and comparing the results, however that is pretty obviously not going to be useful :/


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## joshuaho96 (Jul 14, 2016)

It should be possible to test the Link for scatter with a base map, you need both load and RPM to kill an engine. I would just start slow and run conservative settings (10 deg btdc, 11:1 AFR on boost) for your test and start with testing in neutral. A smooth increase in neutral from idle to 8000 RPM on a warm engine will probably show the problem if it exists.


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## proline (Nov 21, 2002)

That sounds doable and would potentially save a wasted dyno session. If I understand correctly I will be able to test using a base map with the car in neutral and stationary (obviously). If I want to test on the road I will need to use conservative settings like those you have indicated to avoid engine damage. If it is not already clear this is not my area of expertise!


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## joshuaho96 (Jul 14, 2016)

Yeah, you would just have to be careful with how you use the throttle. I don't have the Link base map but I assume the stock timing values in the base map are conservative. Your primary concern will be fueling, start at idle and make sure you stay around 0.95 to 1 in lambda or 14.0 to 14.7 AFR with gasoline. Open the throttle very slowly and back off if you find that the engine is starting to lean out, add fuel/VE at the load/RPM cell where you started leaning out. 

This all assumes you're running in neutral. It won't take much throttle to have enough air to reach redline in neutral. But as you approach full throttle and and you start approaching full load you want to target more like 11:1 or 12:1 AFR to keep combustion temperatures down and avoid pre-ignition from excessive temperature or spark knock.

If you're still on the stock ECU you can use Consult to look at position and reference signals supposedly, if you see a lot of RPM variation then you know you have a problem.


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## proline (Nov 21, 2002)

Yes I do have a standard ECU (with Middlehurst 1Bar chip). I have uploaded a chart of RPM v Time Interval (0.035s) taken from a recent road run. This was logged using a Consult plug and ECUTalk. It's top gear acceleration over 4.5 seconds but unfortunately only to a max of 7250 rpm. Not sure yet but I don't expect to be going much above 7500rpm (certainly not above 8000rpm) after the upgrades.










Link: Scatter

If this is a valid test of scatter then to my untrained eye it doesn't look that bad compared to other examples I have seen. There's certainly some fluctuation but as I understand it this is always present it's just how bad it is.

Would welcome your thoughts.


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## joshuaho96 (Jul 14, 2016)

Seems ok, hard for me to say.


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## Sub Boy (Jan 28, 2008)

Count the amount of crank trigger or CAS replacement kits on the market for RB's (and other engines).....they are not made just because Link has an issue with the CAS.


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## joshuaho96 (Jul 14, 2016)

I agree, but there are a lot of things that are changed for convenience. The optical CAS system is solid but lots of people don't want to deal with fixing it or their ECU isn't really designed to read it.

I think a trigger kit is 100% worth it if you run over stock rev limit. But if you're within the bound of stock rev limit it's arguably easier to run an ECU that doesn't struggle with reading a high resolution sensor and keeping the CAS drive mechanism + timing belt in good repair vs tearing out things that you may not be able to revert to stock easily.


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## Sub Boy (Jan 28, 2008)

joshuaho96 said:


> I agree, but there are a lot of things that are changed for convenience. The optical CAS system is solid but lots of people don't want to deal with fixing it or their ECU isn't really designed to read it.
> 
> I think a trigger kit is 100% worth it if you run over stock rev limit. But if you're within the bound of stock rev limit it's arguably easier to run an ECU that doesn't struggle with reading a high resolution sensor and keeping the CAS drive mechanism + timing belt in good repair vs tearing out things that you may not be able to revert to stock easily.


I guarantee that 99% of people that buy trigger kits are not looking to run past factory rev limits


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## Lith (Oct 5, 2006)

joshuaho96 said:


> Do you have evidence of this? Posts like this suggest to me that some ECUs have more work done to them (filtering, plausibility checks, etc) to read the CAS properly than others: https://www.sau.com.au/forums/topic...n-rb2630/?page=3&tab=comments#comment-6366796
> 
> "I'm having this trigger issue at 5000rpm on my rb26 and need to get hold of a 24 slot trigger disc for my cas. I'm having the problem as im running a vipec v44 ecu. For people's information we tried haltech platinum series ecu and its able to read the signal no problems so its an ecu dependant problem"


I don't know for sure, and to be fair - either side of this argument is postulating about the cause but I think I mentioned it earlier but I think there is a VERY strong possibility that the Haltech is just doing heavy filtering. The trick with this is it doesn't mean it fixes the issue, it just makes it look prettier or hides the symptoms. The more steady state the rpm are the more accurate it will be, in the same way as going to a 24-tooth (or less!) trigger wheel would do but in transient conditions it would be drifting further off reality. It'll be less erratic, but is consistent timing/fueling better even if its way off the mark?


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## joz (May 29, 2017)

i like this thread.

lots of insights about the cas


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## Cris (Sep 17, 2007)

Lith said:


> I don't know for sure, and to be fair - either side of this argument is postulating about the cause but I think I mentioned it earlier but I think there is a VERY strong possibility that the Haltech is just doing heavy filtering. The trick with this is it doesn't mean it fixes the issue, it just makes it look prettier or hides the symptoms. The more steady state the rpm are the more accurate it will be, in the same way as going to a 24-tooth (or less!) trigger wheel would do but in transient conditions it would be drifting further off reality. It'll be less erratic, but is consistent timing/fueling better even if its way off the mark?


This had always been my assumption. Some ecus will apply a smoothing factor to the signal.

Whilst smoothing out the signal will make the engine work it seems like papering over the cracks. Surely fixing the problem is the answer? And don't call me Shirley.


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## joshuaho96 (Jul 14, 2016)

You only need precision to stay in the correct load cell for the timing tables. Filtering does increase SNR and can achieve that precision depending on how bad the noise is.

Trigger kits can be useful but if the CAS was untenable for a stock RB26 everyone would be running a trigger kit.


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## Lith (Oct 5, 2006)

joshuaho96 said:


> You only need precision to stay in the correct load cell for the timing tables. Filtering does increase SNR and can achieve that precision depending on how bad the noise is.


For sure, this is why I suggested that some ECUs do more signal filtering from the outset - steady state at 3500rpm between an ECU which has a fair bit of filtering and one which doesn't will make the one without such filtering look like a relative mess, which in that situation is a reasonable statement as the one with filtering WILL be much more accurate.

The trick here however, is if a car with a fair bit of power gets the throttle applied heavily at low rpm in a zone where the engine may build both boost and rpm quickly - so not just rpm, but rpm rate of change itself changes dramatically. The filtering will absorb some of the rate of change, meaning that heavy filtering will effectively trail behind what is actually happening. I suppose at least the ignition advance applied is likely to be less instead of more - which is less likely to hurt a motor, but yeah - not perfect either. The fuelling would be affected a bit too, I'd imagine.


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## AlexJ (Apr 3, 2003)

the amount of filtering required to smooth a bad CAS setup, oscillating 500rpm at 6000rpm say, will indeed dull the ecu's response to genuine fast crank accelerations. the question is, do you ever see such accelerations in the real world? a typcal dyno ramp rate of 500rpm/second is too slow for the filtering to be an issue wrt accurately representing the crank position. but this is meant to represent something like a pull in 4th gear on the road. First and second gear pulls will be quicker through the rpm. Fast enough for the filtering to mean there is a sustained and significant misrepresentation of actual crank position?

I sense Link could apply the same filtering as haltech, the dsp/mcu power is available, but they have taken a position that fidelity to the trigger signal is the higher priority. i don't think that helps them when the keyboard warriors get stuck in.

My cas scatter got worse overtime and I went to a full crank trigger kit. I feel much better but I doubt it has made much different to performance or durability of the engine.


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## joshuaho96 (Jul 14, 2016)

A basic low pass filter like a Buttersworth that you guys are thinking of is indeed only going to be able to filter high frequency data and represents a tradeoff between steady state and transient behavior outside of the simple case where noise is mostly above the signal frequencies.

But wavelet filtering is specifically designed for the problem you guys are talking about, which is transient behavior. Transient features are retained in wavelet denoise as their primary application is image processing where sharp transients usually represent edges in the image: https://www.mathworks.com/help/wavelet/ug/wavelet-denoising.html

I can't say whether Haltech is doing any of this (maybe they are, maybe they aren't) but the problem you guys are mentioning is not intractable, smartphone cameras have truly horrendous raw signal but they have incredible amounts of image signal processing behind them to clean up the image and make it into something that doesn't look half bad.

Again, I think a crank sensor kit is a great upgrade if you find that you need it, but if the stock CAS was fundamentally flawed in the context of a stock GT-R you would see just about everyone running a trigger kit.


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## Lith (Oct 5, 2006)

joshuaho96 said:


> Transient features are retained in wavelet denoise as their primary application is image processing where sharp transients usually represent edges in the image:
> 
> I can't say whether Haltech is doing any of this (maybe they are, maybe they aren't) but the problem you guys are mentioning is not intractable, smartphone cameras have truly horrendous raw signal but they have incredible amounts of image signal processing behind them to clean up the image and make it into something that doesn't look half bad.


Not really a comparable situation at all. We are talking about real-time filtering, where you need a reliable result before you get to look at the rest of the picture you'll be dealing with. It'd be fine if you could log all the trigger data for a session of engine operation, smooth it, then play it back after the fact - like what the filtering in the article there is pretty much about, but you only have right up to this moment... which is why if there is a big rpm transition and there is heavy filtering, it may eliminate the initial upwards "blip" as noise as it hasn't acquired enough data to identify a new slope.


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## joshuaho96 (Jul 14, 2016)

Pretty much any filter I can think of has a notable phase delay, you just end up comparing how much extra delay a given filter adds compared to others and figuring out your max allowable phase delay.

Keep in mind that these microcontrollers are operating at something like 200 MHz whereas the engine is running at maybe ~200 Hz. For each individual slit you get one RPM data point, then another once you get the cylinder sync pulse. With 360 cam pulses that you get 180 crank pulses per revolution, you only need 1 canonical load RPM per crank revolution to determine spark timing and target AFR.


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## Cris (Sep 17, 2007)

AlexJ said:


> ...I went to a full crank trigger kit. I feel much better but I doubt it has made much different to performance or durability of the engine.


I fancy that this is the reality of the sitaution for many. Crank triggers seem to be more reliable solution than the CAS. Much like the MAFs. They are not fundamentally flawed but seem less relaible than MAP sensors.

Of course once my crank trigger is fitted I'm expecting another 200bhp. Or, at least, that's what I'll be saying down the pub...


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## joshuaho96 (Jul 14, 2016)

I would be curious to see if anyone has done CAS + crank trigger simultaneously and graphed the two. Even 36-2 wheels don't have the sheer resolution of the CAS, I'm guessing there would be some value to going from CAS at low RPMs to blending into the crank sensor at high RPM for setting ignition timing.

Lots of turbo engines out there run both MAP + MAF for redundancy and to avoid the pitfalls of each method of load sensing.


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