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Thread: Scot from Haltech Nissan CAS info video

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    Member ANDY black s13's Avatar
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    Scot from Haltech Nissan CAS info video

    RB20/25/26 & CA18det, info relates to the SR20 aswell,
    they mention belt deflection on big power lumpy camed RB's suffer about 8 degrees of timing retard and power lost
    do CA18's suffer the same loss is power? https://www.youtube.com/watch?v=mh4hxnfMfGA
    just digs in and fecks off
    UPDATE 26/04/15: Black '92 s13 (Still)awaiting new engine! Now doing full interior/loom strip,2015 still making things and aiming for less than 1000kgs,White '99 14a has the 23k engine from the blue 1 now fitted + lots of new bits (to be Mot'd then up for sale)2015 still not done,lost interest want to get the 13 done 1st,Blue '99 14a 23k sold as rolling shell 03/14,Green '99 14a gone now RIP jfc,2015 Was Daily driving my daughters 1.0 Yaris ,Now replaced with another yaris SR 1.3 for daily (fun) runabout
    "I think that in any racing engine,The nearer you are too it Disintegrating,
    In general the better its performance will be" Keith Duckworth Cosworth DFV and other Cool stuff

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    Strange thing is that if the stock ECU detects detonation or the sensor is short circuit (unless replaced by high ohm resistor) it retards the timing. I don't know by how much but around 10 degrees was claimed. Video says "high power" engines run near the detonation limit. Video also doesn't say that some det events can't be heard by ear but a piezo sensor will hear them.

    The CAS isn't to blame it's the "rubber band" cam belt. The core of the belt isn't a "rubber band" it's KEVLAR and it doesn't stretch every time the engine is revved hard. If the belt "stretch" causes retard then the cams also retard (Haltech don't seem to be leaping in to fix that). 7.5 degrees is 1/2 tooth, 1/2 a tooth in 48 teeth between crank and cam is 0.01 (1%) strain in the belt. I think this claimed elastic [1] "stretch" is highly improbable. It's well beyond the limit of elastic proportionality of KEVLAR - belt will be permanently stretched, engine would be retarded and stay retarded. At the limit of elastic proportionality 0.005 (0.5%) there would less than 4 degrees of timing change and I'm fairly sure that no one runs timing belts anywhere close to that. l'd hope about 1 degree and 25% of the limit of proportionality = factor of safety of 4. It may stretch a bit as it ages over 60K miles / 5 years.
    https://www2.lbl.gov/ritchie/Library...nDependent.pdf

    The condition they describe will apply to ALL belt driven cams.

    CAS has 4 "home windows" one for each cylinder, the windows are different sizes and the ECU counts 1 degree pulses during window "open" period, this tells it which cylinder it's on. Engine only has to turn 1/2 revolution for a "window" to move past the sensor and ECU to start running engine. After market missing tooth from crank sensor wheel may have to turn a full crank revolution to get the reference and start running engine. A single cam "home" signal with fully toothed crank sensor may have to turn 2 revolutions before ECU can start running engine. (Though the camshaft magnet in the video appears to have 2 teeth, one turn of crank but this means they can only run in bank fire mode and not sequential.)

    Nearly all after market ECU have much lower resolution of engine position. At best they have 36 teeth on crank, that's 72 on/off signals for each revolution, 5 degree resolution. Video 12 teeth on crank is 24 on/off for each revolution and a (frankly laughable) 15 degree resolution. They then have to "estimate" based on engine speed where it really is. But actual engine rotation speed slows as it comes up on compression and speeds up on first 1/2 of power stoke so they have to "guess" [2] where the engine is, 15 degrees is a lot of rotation time to be guessing. Nissan CAS has 360 slots, 720 on/off signals for each cam revolution and ONE degree resolution of engine position. I'm not sure if it does any guessing or if timing changes in 1 degree steps (I think the latter). The Nissan CA18DET ECU runs off a "timing chip" (fiendishly cunning and complex device) and the CPU only determines the position that it programs the timing chip with.

    [1] Elastic - the material recovers it's original length when stretched and released. If the "elastic limit" is exceeded the deformation is permanent and the material has "yielded".

    [2] "guess" requires a fast and powerful CPU and a 4D acceleration curve v's rpm v's load.

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    Quote Originally Posted by skyshack View Post
    Strange thing is that if the stock ECU detects detonation or the sensor is short circuit (unless replaced by high ohm resistor) it retards the timing. I don't know by how much but around 10 degrees was claimed. Video says "high power" engines run near the detonation limit. Video also doesn't say that some det events can't be heard by ear but a piezo sensor will hear them.

    The CAS isn't to blame it's the "rubber band" cam belt. The core of the belt isn't a "rubber band" it's KEVLAR and it doesn't stretch every time the engine is revved hard. If the belt "stretch" causes retard then the cams also retard (Haltech don't seem to be leaping in to fix that). 7.5 degrees is 1/2 tooth, 1/2 a tooth in 48 teeth between crank and cam is 0.01 (1%) strain in the belt. I think this claimed elastic [1] "stretch" is highly improbable. It's well beyond the limit of elastic proportionality of KEVLAR - belt will be permanently stretched, engine would be retarded and stay retarded. At the limit of elastic proportionality 0.005 (0.5%) there would less than 4 degrees of timing change and I'm fairly sure that no one runs timing belts anywhere close to that. l'd hope about 1 degree and 25% of the limit of proportionality = factor of safety of 4. It may stretch a bit as it ages over 60K miles / 5 years.
    https://www2.lbl.gov/ritchie/Library...nDependent.pdf

    The condition they describe will apply to ALL belt driven cams.

    CAS has 4 "home windows" one for each cylinder, the windows are different sizes and the ECU counts 1 degree pulses during window "open" period, this tells it which cylinder it's on. Engine only has to turn 1/2 revolution for a "window" to move past the sensor and ECU to start running engine. After market missing tooth from crank sensor wheel may have to turn a full crank revolution to get the reference and start running engine. A single cam "home" signal with fully toothed crank sensor may have to turn 2 revolutions before ECU can start running engine. (Though the camshaft magnet in the video appears to have 2 teeth, one turn of crank but this means they can only run in bank fire mode and not sequential.)

    Nearly all after market ECU have much lower resolution of engine position. At best they have 36 teeth on crank, that's 72 on/off signals for each revolution, 5 degree resolution. Video 12 teeth on crank is 24 on/off for each revolution and a (frankly laughable) 15 degree resolution. They then have to "estimate" based on engine speed where it really is. But actual engine rotation speed slows as it comes up on compression and speeds up on first 1/2 of power stoke so they have to "guess" [2] where the engine is, 15 degrees is a lot of rotation time to be guessing. Nissan CAS has 360 slots, 720 on/off signals for each cam revolution and ONE degree resolution of engine position. I'm not sure if it does any guessing or if timing changes in 1 degree steps (I think the latter). The Nissan CA18DET ECU runs off a "timing chip" (fiendishly cunning and complex device) and the CPU only determines the position that it programs the timing chip with.

    [1] Elastic - the material recovers it's original length when stretched and released. If the "elastic limit" is exceeded the deformation is permanent and the material has "yielded".

    [2] "guess" requires a fast and powerful CPU and a 4D acceleration curve v's rpm v's load.

    hmm, even better approach than mentioned yout video...well done

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    Member ANDY black s13's Avatar
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    I clicked on the video as I had endless problems with the CAS splines wearing many years and thought they would mention that and the timing wander issue
    when they went onto the dreaded power loss I was a bit surprised as not read or heard of it before on the rb or any belt driven car engine enough to cause a loss

    many years back this came up in the world of ford pinto tuning and later the cossie yb200 and tests if I remember were similr to a chain
    as in both had near zero strectch at operating loads ,so I think they are leading us astray a bit saying the belt stretches

    it was the belt deflection bit they mention, I'm not convinced it can deflect or move at all when its going up the rev range
    thinking how fast the thing is spinning,it's under load can it really move and alter cam timing?

    read about lots of rb builds and not something thats come up when chasing high power,
    the RB has many issues tbh but at most a swap to a Greedy or Gates racing Belt is only thing done regards the belt
    and it's changed to a more reinforced belt as a 'hold it together because it cost a lot' mod not because the stock belt stretches

    so I wont be designing some sort of super close fitting belt guard just yet, I might see if it's come up as an issue on RB's or other engines
    just digs in and fecks off
    UPDATE 26/04/15: Black '92 s13 (Still)awaiting new engine! Now doing full interior/loom strip,2015 still making things and aiming for less than 1000kgs,White '99 14a has the 23k engine from the blue 1 now fitted + lots of new bits (to be Mot'd then up for sale)2015 still not done,lost interest want to get the 13 done 1st,Blue '99 14a 23k sold as rolling shell 03/14,Green '99 14a gone now RIP jfc,2015 Was Daily driving my daughters 1.0 Yaris ,Now replaced with another yaris SR 1.3 for daily (fun) runabout
    "I think that in any racing engine,The nearer you are too it Disintegrating,
    In general the better its performance will be" Keith Duckworth Cosworth DFV and other Cool stuff

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    I <3 BBS LM Actual_Ben_Taylor's Avatar
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    Come on skyshack you've been on here long enough to know all about CAS issues with worn splines on exhaust cams...

    In an ideal world blah blah, but 30 year old engines...

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    Member ANDY black s13's Avatar
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    Exhaust cam CAS drive spline wear is a given on the CA,the fix is just a camshaft with good splines and an unworn CAS and lube the splines
    and a good tight fitting 'O' ring on the CAS drive to possibly further resist it trying to move on the splines,

    I'm still curious if anyone else has a take on the claimed power loss from belt deflection
    and it retarding cam timing as the belt (or chain) is rapidly moving
    if the rapid belt/chain movement alters timing,
    then the same rapid movements are rapidly altering the timing back and forth between perfect timing
    its not one constant timing swing like they sort of suggest causing a loss in power,
    it would be multiple times every stroke

    if you had a calibrated crank pick up/sensor and a cam signal pick up upon each cam it could be montored/data logged
    to actually confirm if it is actually swinging the timing at any point of the rev range,
    I haven't found any testing like that so far
    Last edited by ANDY black s13; 22-03-2019 at 20:19.
    just digs in and fecks off
    UPDATE 26/04/15: Black '92 s13 (Still)awaiting new engine! Now doing full interior/loom strip,2015 still making things and aiming for less than 1000kgs,White '99 14a has the 23k engine from the blue 1 now fitted + lots of new bits (to be Mot'd then up for sale)2015 still not done,lost interest want to get the 13 done 1st,Blue '99 14a 23k sold as rolling shell 03/14,Green '99 14a gone now RIP jfc,2015 Was Daily driving my daughters 1.0 Yaris ,Now replaced with another yaris SR 1.3 for daily (fun) runabout
    "I think that in any racing engine,The nearer you are too it Disintegrating,
    In general the better its performance will be" Keith Duckworth Cosworth DFV and other Cool stuff

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    They swapped the CAS. I ass u me ed that they would have been working with a fairly fresh build. "high power" suggests new high lift cam so will have new cam splines. I would hope they checked the crank keyway, must have seen it when they put the 12 tooth wheel on unless they did it with their eyes shut.

    The power the engine makes doesn't affect the cam timing or belt tension. It's simply down to cam inertia "I", acceleration "a" (I^2a) and cam profile lift "x", engine speed "v", valve spring rate "K" (Kxv). So they will have high lift cams with a more aggressive profile and possibly stronger springs but that's not going to create this sort of issue.

    Having an inertia dyno that doesn't load the engine enough or having slip on rollers so it accelerates much faster than it will when tyres have grip on track would affect belt load. (But pulling the timing so engine makes less power is called "traction control".)

    So I'm pretty sure that they have observed OEM ECU detonation detect page EF&EC-17.
    This says it pulls the timing additional 5 degrees retarded from knock map (LOW octane map on CA). IF they have knock map that is 5 degrees retard then they get 10 degrees.
    http://forum.nistune.com/viewtopic.p...8aeaf&start=30

    Not RB as this is CA specific. "These days we remove knock maps from this vehicle with feature pack updates, so just one set of maps (Nissan did this for Europe). ECU will still retard timing on knock count, but nothing beats properly tuning the vehicle to avoid needing this backup feature"
    http://forum.nistune.com/viewtopic.p...=2027&start=30

    On a JDM CA18DET ECU and loom there is a signal for the turbo boost solenoid which could be used to indicate that it had switched to the LOW octane map. Euro Hi and Low octane maps are the same, JDM are for 96 Ron and 89 Ron, based on increasing knock count ECU will shift timing to lo map. If that knocks as well it pulls the timing, don't know where that is but it's separate to the 2 ign maps or factored off knock count. Knock count gets forgotten every time ECU is switched off so it re-calibrates to the fuel mix every time it runs.

    It may be 8 bit 1 MHz but it's still quite clever (as the timing chip does the grunt).

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