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standalone question on 99
So I have a 99. I got a boomslang harness, and have a simple question. If I were to put a MS on there, I need a CAS from a 97? Is this only an issue when using MS? What about people who use a Hydra? What other sensors do I need to use when bypassing the stock computer? The CAS is just for a timing signal, right? So how does a stock 99 get a timing signal? and why can't a MS read this signal?
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If you have some control over how the ECU reads the crank trigger and cam sync signal, then the '99's sensors are superior to a CAS.
You can make the '99 outputs similar to the CAS by grinding off two of the crank trigger teeth (@10deg BTDC IIRC), and grinding off the double trigger teeth on the intake cam gear. I don't believe that the MS needs the cam sync signal since it isn't sequential injection, and the ignition is wasted spark, so you could probably just use the crank trigger wheel if you can configure it to read the hall effect sensor's output. |
Dammit, Beavis...
First off, the limitation is a software one, not an electrical one. The code for the MS1 CPU cannot accommodate unevenly spaced crank trigger signals, and the teeth on the NB wheel are not evenly spaced- there are two at TDC, and two at seventy-something BTDC. So to make an NB crankwheel work with an MS1, you grind off the two teeth that are at TDC. The MS2 software is much more advanced in this regard, and it can use the NB crankwheel signal as-is. In fact, there's a preset in the trigger configuration window specifically for NB sensors. You just select that and you're done. Now, all ECUs require a cam signal of some kind in order to do wasted-spark, regardless of whether you're running sequential injection or not. The ECU has to know which crank pulse corresponds to firing #1/4 (before TDC) and which corresponds to firing #2/3 (before BDC). The stock cam sensor (both NA and NB) gives a pulse before #1/4 TDC, so that the CPU knows where to steer the next crank pulse that it gets. In order to run sequential injection, you actually need to go a step further and get rid of one of the two cam pulses, or at least be able to distinguish between the two. The ECU needs to get a distinct cam pulse which it can use to determine which cycle each cylinder is in in order to trigger that injector at the correct time. With the stock ECU, it makes this determination based upon the fact that on the NA, one CMP signal is longer than the other and on the NB, the #1TDC CMP pulse is a double-pulse, whereas the #4 TDC pulse is a single pulse. The Hydra may know how to deal with this, I honestly don't know. The MS1 requires a single cam pulse to make this determination, it can't measure the length of the cam pulses. So, to answer the OP: If you install an MS1, in standalone, you'll need to cut two teeth off the crank wheel. You can't run an MS1 in parallel on an NB without a CAS. If you install an MS2, you're good to go with no modifications and no need for a CAS. |
Originally Posted by Joe Perez
(Post 286274)
Dammit, Beavis...
Now, all ECUs require a cam signal of some kind in order to do wasted-spark, regardless of whether you're running sequential injection or not. The ECU has to know which crank pulse corresponds to firing #1/4 (before TDC) and which corresponds to firing #2/3 (before BDC). The stock cam sensor (both NA and NB) gives a pulse before #1/4 TDC, so that the CPU knows where to steer the next crank pulse that it gets. So, to answer the OP: |
Great! My idea was to run MS II in parallel, and the answer is...I can. Thanks for the responses guys. So what is the difference between 3.0 and 3.57? I read that the 3.0 is easier to mod? I just want to buy the right stuff, that's all...
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As a general rule, stay away from parallel set ups. Lots of people do them, but they are riddeled with problems, they are a slow start, and a much bigger pain (and slightly more costly) to do. If you have a good reason for it (the most typical is smog) then maybe it makes sense, but if you can set up the car to switch back and forth I'd say it's the way to go.
I'd say, in an ideal world, a missing tooth wheel is the way to go, my feeling is (I plan to do this myself someday but have yet to try it) the stock NB sensor would work FINE for this, just add the wheel and remount the sensor, use the same input circuit. However, to just get up and running with as few mods as possible, and to keep the car so you can jump from MS to OEM ecu's, buy an MS-II and do everything in there, change nothing on the motor. |
I knew I forgot something. More or less, the 3.57 is just prebuilt and surface mount. Which means it's much harder to mod. I would shy away from it as much of what's on the MS-board you're going to want to change. If you're very comfortable soldering onto surface-mount-devices (SMD's) then you could potentially get it, but odds are you're better off with the 3.0. Otherwise they are basically the same.
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Originally Posted by DammitBeavis
(Post 286351)
Sorry, it's been a while since I did a non-sequential. I was thinking of the missing tooth wheels like the TECII use. They don't need a cam signal since the missing tooth defines which pair of cylinders is approaching TDC.
To do fully sequential ignition, the system also need to know the absolute position of the cam. This cannot be achieved with a missing-tooth crankwheel. You can use either a missing-tooth camwheel (by itself) or an even-tooth crankwheel and a camwheel which gives only one even per cam revolution, which is to say one event for every two crank revolutions. The stock NA CAS and NB cam sensor provide two events per cam revolution, which from the MS's point of view is the same as one event per crank revolution. The events are slightly different in duration, however. The stock ECU is programmed to recognize this, doing the same with an aftermarket ECU requires some work, and is only really necessary for full sequential. In the most basic config, the MS overlooks that difference and treats the cam events the same. The MS1, in particular, cannot measure secondary trigger event duration, it just resets a crank counter every time it sees a cam pulse. The MS2 is a bit more sophisticated and could in theory decode the camwheel properly, though I've never tried it as it's not terribly important to do so.
Originally Posted by AbeFM
(Post 286385)
I'd say, in an ideal world, a missing tooth wheel is the way to go, my feeling is (I plan to do this myself someday but have yet to try it) the stock NB sensor would work FINE for this
Originally Posted by thirdgen
(Post 286363)
So what is the difference between 3.0 and 3.57? I read that the 3.0 is easier to mod? I just want to buy the right stuff, that's all...
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Well, one good thing about the OEM '99 set up, with only 4 teeth, there's a lot more CPU time left over for running all the other gizmos. Sure, you're timing errors get larger, but I've yet to see a comparison of the additional teeth and what it does to accuracy. Some day I might runboth just to see how they compare.
One advantage to the missing tooth, though, the car will start faster. The MS-II's handling of the NB miata is functional, but not perfect. I would say it's plenty good to run the car, though. They just don't do a switch from wasted fuel/spark to sequential, and even in wasted mode they still "think" in sequential, which means 2-3 full revolutions until the motor starts. Not a big deal, you just get used to holding the key for a full second. Other than that, it starts right up and runs fine, just like a normal car. |
Actually, fewer teeth does not necessarily give you more error.
The trick is to have the tooth just before the ignition event, with just enough time for the ECU to perform it's calculations. With slow ECU's you want your crank trigger around 70deg BTDC since the max advance is normally around 40deg. That gives the ECU 30 crank deg to do it's work, and the calculation should be spot-on. With faster ECU's, triggers at something like 60deg BTDC are ideal. Unless you have a super-fast ECU, it can't start it's calculations much later than that anyway no matter how many teeth you have. And unless you're running an engine with very low rotating mass like a motorcycle, the crank accel/decel in those 20 or 30 degrees is negligible anyway since there won't be a firing event during that period. |
Originally Posted by DammitBeavis
(Post 286780)
Actually, fewer teeth does not necessarily give you more error.
My heavy arse engine with HEAPS of inertia gets around 7000rpm/second delta RPM, the most insane engines get around 36000, my logs are poor, I can probably beat that, possibly by as much as two times. Do the math and post again for your final 51% and a chance at a passing grade ;-) Fred. |
Hehehe.
On the MS1, it does not matter how many teeth your wheel has. Only two of them are declared to be trigger teeth for the purpose of driving the countdown to ignition- the others just increment a counter. On the MS2Extra, there is some rather interesting intelligence at work. Let's say you have a two tooth wheel, and each tooth is at 60° BTDC. When that tooth comes around, the CPU starts a timer and counts down the calculated number of microseconds it believes it will take for the correct firing position to come around. If it wants to fire at 18° BTDC, then it's got to rely on counter precision alone for 42° worth of rotation, and pray that the crankshaft's angular velocity remains constant during that time. Now say you've got a 36-1 wheel, with one tooth every 10° of rotation. As before, we want to fire at 18° BTDC. Now, the ECU does not start the timer on the 60° tooth, it waits until a later tooth comes around, so it spends less time free-running on the timer. It'll still use a "reference" tooth to do the dwell calculation (figuring out when to start charging the coil) however for the actual moment of firing, it'll wait until the 20° tooth comes around and then only have to free-run on the timer for 2°. One other benefit of a large tooth count is that you can do much more accurate timing during cranking. Rather than the CPU having to do any timing at all, it simply fires the ignition exactly on a particular tooth. With a 36-1 wheel, you can specifiy cranking timing in multiples of 10°, with a 60 tooth wheel, you can work in multiples of 6°. |
Joe gets 75% so far, and a bonus 10% for his accurate and correct supplementary information :-) To hit 110 from 85, what is the final piece of the puzzle Joe?
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I think if you're building a lot of stuff from scratch, and don't mind the work, you're better off with the missing tooth approach. If MS handled it better, then a non-missing tooth and a cam wheel would be IT. Which is what many car manufacturers do. :-)
Runnnig a CAS is not recomended, getting away from that is one of the few changes mazda made - a company so unwilling to change thought it was the one thing really worth doing. And certainly, if you're pushing the motor to it's limits (and if you're not, what are you doing here?) you might as well take what you can get. And, as a bonus, there's a recorded "prediction error" to the timing of the MS-II, so I have lots of logs which I should digest and post, but I imagine with more teeth this would be smaller - at LEAST by as much as 1/tooth count. |
That is simply what I was told by Autronic when I was deciding if I should modify my my stock triggers, or use the 60-2 wheel that was already mounted on the crank pulley. I'll ask them for an explanation. I don't have the math, just the word of Ray Hall.
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You are correct about the angular precision, however because of the large gap from the last sample, you have pretty much no idea what the engine is currently doing even if you DO know where it is. That should be a clear enough and simple enough explanation.
In practice though, you are right, if it's aligned well enough, it should be fairly good. The bit Joe covered about using the closest tooth it the important part of the upgrade timing wise as according to Ken the RPM is only calculated once per rev anyway in ms2e. I was a bit shocked/surprised by that, but it runs my engine well, so who cares :-) EDIT : and of course, the 25% Joe scored was for his cranking example. short term RPM variation while cranking is HUGE, esp with high compression. Fred. |
http://www.google.com/search?hl=en&s...00&btnG=Search
If you stand on the gas in your uber light weight machine at 900rpm you'll have around 100rpm error in your lookups which doesn't matter all that much I guess. At higher revs it becomes negligible. The timing error will be more significant at low rpm too and that will matter a bit at least. So in summary, it doesn't actually matter that much while actually driving, but there are four aspects to it :-) Fred. |
I would imagine a reasonable calculation would include rate of change data from previous triggers. Either way, I posted the question to the Autronic/Motec folks, and I'm bound to at least learn something new.
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I know from what logs I looked at back when I was checking out my triggers more closely, certainly low RPM (<2k) the errors were big, and idle they were ALL over the place. MS-IIe uses some predictions, though there's debate from the authors about which you should use.
The simplistic way to view it, if you've got a motor that's slowing over 1/4 of the revolution, lots of teeth will mean your last bit of error is in how long it takes it to cover 6*. 4 teeth means your error in how long to cover 90*. 10% of 6* is <1 degree, 10 % of 90* is nearly 10 degrees. The less often you update the rpm, the more you want to have a lot of teeth. How much does it matter practically? Sure, all this stuff seems to have no effect, but if you're trying to get <1* accuracy on spark timing, then you'd better be confident your average speed does't loose count over the 30 or 40 degrees you're going to cover, and that means knowing RPM within 2.5%. What is the second derivative of engine speed? Got me. :-) (edit): The nice part about very few teeth is the errors in reading them don't play much of a factor. Of course, this can be overcome with averaging, but you're going to come to a point where you're getting computationally expensive |
So I was gonna start out by purchasing a MS II with a 3.0 PCA, this all comes pre-assembled? Is there any thing else I need to order from DIY autotune with this? I was also thinking about maybe not going with MS II, but maybe a different standalone like a Microtech LT-8. What do you guys think?
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Given the support, the capabilities, and the cost, there's no good reason not to go MS - there's not much the other systems do the MS doesn't - unless there's some feature you want, go ms. And, since it's open source, well... I didn't like the input circuits, I made my own. I didn't like the way it idled, I wrote my own idle routine.
The board comes assembled or not. It's your choice, but you learn a lot more about how it works if you do it yourself, so I'd recommend it. Besides, you're going to have to do minimal modifications on it anyway, so you might as well know what's what so as to be more comfortable. |
Told ya I'd post when I found more info. I found a response to error vs. trigger wheel teeth. This is from Ian, one of the guys that knows how the guts of the Autronic systems works. I'm not sure how much of this is applicable to other systems:
Originally Posted by Ian
(Post 81)
There are a few other things that need to be considered before everybody starts fitting multiple extra teeth to all their cranks.
All Autronic ECUs do a Load measurement at the same time as the Cylinder Pulse that occurs at the Cylinder I/P Lead angle. When the Trigger Events / Cycle value is the same as the number of engine cylinders (a normal configuration) then a Load measurement is taken at the same relative point on every cylinder. For example if the Cylinder I/P Lead angle is 60 deg then a Load measurement will be taken at 60deg BTDC on every cylinder. This means the Load value will be most stable because manifold reversion pulses, etc will also be occuring at the same relative times on each reading. If you increase the number of Trigger Events / Cycle then the ECU will also be taking additional Load measurements. If you double the Trigger Events / cycle there will be two Load measurements per cylinder NOT at the same relative positions. If you have a 4 cyl engine with 60deg Cyl I/P Lead there will be alternating Load measurements at 60deg and 150deg BTDC effectively on each cylinder. If there is a significant reversion effect in the manifolding this may appear as an unstable Load reading (which some other ECU's seem to have as standard). This will also affect Manifold Rate fuel trims if the cal is using that in a Trim table. Extra Trigger Events / Cycle could also have a similar effect on Ignition timing. A lot of people are aware that if you set a flat ignition table and watch the timing with a timing light when you suddenly accelerate the engine with no load you will see an Autronic retard the first pulse and then be correct for the rest. This is with one pulse per cylinder. If you do the same test with other ECU's and one pulse per cylinder you will see the timing retarded the WHOLE time the engine is accelerating. If you fit three pulses / cylinder to these engines for the other ECU's the retard effect nearly goes away. The Autronic has a very good predictive timing algorithim that works with one pulse / cylinder. Engines do not run continuously smoothly even though they appear to. They slow down on compression strokes and accelerate on combustion strokes. Introducing extra Trigger Events / Cycle could destabilise the predictive timing in a similar way to the Load calculation. Using a camshaft driven Cylinder pulse has the same effect (seen as timing scatter). All Autronic CPU's up to SM4 v1.05 (& all SMC /SM2) do the prediction the same way...
Originally Posted by Ian
(Post 85)
For the purpose of this thread the v1.06 and onwards have an additional parameter called the Digital Angle Filter. When set to Fast it operates the same as earlier SM4 & SMC / SM2 CPU's. When set to Slow the prediction is averaged over more Cylinder Pulses to minimise scatter.
Also when using dwell the v1.06+ has a wider tolerance than v1.00-v1.05 before applying dwell extension. It is a complex scenario because the dwell pulse may be initiated several Cylinder pulses before the timing point to achieve the desired dwell time. If the engine speed increases suddenly (after initiation of the dwell pulse) and the output is triggered at the correct position the dwell pulse will be shorter than planned. Depending on the coil minimum dwell requirements the short pulse may undercharge the coil resulting in a missfire. Under certain circumstances the SM4 (and the old dwell boards) will extend the dwell to a minimum value to ensure a spark, which will be slightly retarded, rather than risk a spark missfire. In pre-v1.06 CPU's the tolerance was found to be a bit conservative so it (the tolerance) has been widened in v1.06 and later to achieve better timing accuracy when accelerating. For the 6 tooth Subaru crank the Autronic uses the 65deg teeth for all timing. The Subaru uses the 10deg teeth for cranking position. When cranking it turns the dwell on with the 65deg tooth and off with the 10deg tooth. Maybe the Subaru ECU couldn't calculate the engine position accurately at cranking so it needed an extra tooth at the cranking ignition point. That then raises the question of ECU's that require cylinder pulses at the cranking position - how good are they if they need a tooth there? |
Wow, well, the guy knows the insides of the autotronics, you have to say that. Of course, really what he's saying all comes down to how THAT computer handles it. For your computer, I'd go with it. :-)
FYI, though, some European stuff, audis, porsche, etc, use several HUNDRED crank triggers - they read the starter gear on the flywheel. Go figure. Of course, they also have to other references, one is a cam, and the other I'm not sure - both significantly lower. I've also heard that the 300zx uses some obscene number of pulses, over 100 (maybe 150?) on the cam. Really, you can always choose to ignore extra pulses, till simply the computational load of ignoring them becomes to high. However, I tend to agree, certainly reading them in the same spot and some math should get you there - the extra pulses are only for checking your work or looking for something weird (I've heard tell of pre-ignition sensors based on the engine slowing down slightly or at the wrong time.) Er, more to the point, is there anything you need help with? :-) |
All nissan CAS units I've seen have the 360 tooth pattern for sort of rotary decoding style operation. It's for perfectly fast sync up though, not accuracy. Matt Cramer from diyautotune reckons they read all teeth, but the documentation I've seen suggests otherwise.
Pics : diyefi/RPM-engine-position-sensors - Photobucket - Video and Image Hosting |
Originally Posted by AbeFM
(Post 348382)
...Er, more to the point, is there anything you need help with? :-)
I'm installing a built motor and I needed an extra high-speed input for traction control. So I had to combine my crank and cam signals into one input. While I was reading up to find out where I needed to move my cam pulse to, I ran across that and thought I would share. FYI, I ended up grinding all the sensor teeth off the intake cam gear, then drilling and tapping a hole at the new location. I put a M6x1 bolt in from the back and ground the end down to the shape of the original teeth with a dremel. |
total ms noob here, let me get this straight: ms2 will work with the nb crank wheel/sensor and its possible to get it working without installing the n/a wheel and cas?
If that is correct, why are so many members like cjernigan and patsmx5 using the cas or some other sensor besides the stock nb one? |
1) they have ms1?
2) abe scared them off? 3) the nb code isn't fully working yet? Abe had some issues which were probably mostly his own fault :-p (sorry) but there may have been code issues too. Hard to know, he's using it now anyway AFAIK. Fred. |
thats what I like to hear:)
thanx |
You'll definitely get more accurate timing with your signals coming from the crank too. In fact, if I had a NA I'd convert it to NB sensors. On my DSM with a CAS (same configuration as a Miata) there was nearly a 2 degree timing drift from 1500 to 3500 from belt stretch.
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The Autronic guy unwittingly points to why a 36 or 60 tooth strategy is often considered superior. The ECU sees acceleration and deceleration much sooner. Retard on acceleration is non-ideal, but won't hurt anything but power. On deceleration, a four-tooth sensing strategy can get you significant advance. Think about how quickly an engine decelerates on an upshift, and how much boost could be in the chamber when that spark goes waaaay early. Things can get ugly.
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Originally Posted by DammitBeavis
(Post 348680)
You'll definitely get more accurate timing with your signals coming from the crank too. In fact, if I had a NA I'd convert it to NB sensors. On my DSM with a CAS (same configuration as a Miata) there was nearly a 2 degree timing drift from 1500 to 3500 from belt stretch.
Good post by the other guy with regards earlier signals. Fred. |
Originally Posted by SolarYellow510
(Post 348689)
The Autronic guy unwittingly points to why a 36 or 60 tooth strategy is often considered superior. The ECU sees acceleration and deceleration much sooner. Retard on acceleration is non-ideal, but won't hurt anything but power. On deceleration, a four-tooth sensing strategy can get you significant advance. Think about how quickly an engine decelerates on an upshift, and how much boost could be in the chamber when that spark goes waaaay early. Things can get ugly.
My example was using a clutch-kick during a rallycross in the DSM. Fast full throttle accel with no load followed by a hard decel. In that car it would be even worse because of the CAS, the timing belt, slack in the CAS drive, and the momentum of the cams. I run that thing right at the edge of knock too. 110+*C intake temps, 120+*C coolant temps, 22psi of boost, and as much ignition advance as I can run without lighting up the J&S display. The knock sensors will pickup some noise when I do that, but I can imagine there's a lot of drivetrain bits clanging together during that kind of operation as well. Either way, I'm beginning to feel that it might all be academic. When I began I was told I was using the ideal setup, now that I start to see the holes in the theory, I have to wonder why this stuff has held up so well. I've been running pulse-per-cylinder on a bone stock miata bottom-end @200WHP for 2 years, then ~240WHP for another 2 years. I just pulled the motor to install my new built engine. The bottom end seems fine after 5 years of autocross in SM2 and 30000 hard driven boosted miles. Ringlands look good, no slack in the bearings, and the piston heights are all perfect. I can only assume that there is some law of physics or some invisible engineering wizardry holding things together for me. In fact, the engine that I'm putting in now came from the guy that just sold his turbo kit on this board in this thread https://www.miataturbo.net/forum/t28960/ Hell, he was making ~500HP with a Motec and a stock NA CAS setup on this longblock. If that didn't generate some scrap metal I think I'll be safe with a crank trigger at 350HP. :) |
Originally Posted by rb26dett
(Post 348706)
Not that I disagree with you, but how are you certain that the drift was from the belt and not code prediction or a switch in algorithms at a fixed rpm etc? I don't believe that you can be.
Good post by the other guy with regards earlier signals. Fred. I was actually told (while tracking down an issue with injection phasing) that I should set my I/P lead with the engine in the middle of the rev range rather than at idle if I was going to use the CAS. That's when I found that by setting my I/P lead at 1500 I was about 2 degrees off. He said that all the CAS setups (hall and optical) had drift and scatter issues, but they were pretty consistent once the engine was up to operating temp. He said that you could see the difference in the timing maps after a dyno tune if you compared the same engine using a CAS vs a crank trigger. If you want to see it yourself, set your timing to a fixed 10deg and grab a timing light. Point it at the crank and watch the timing drift and scatter at different speeds. Then point the light at the cam gear and you'll note that it's rock steady (there will still be a bit of scatter from the slack in the drive gear, but no drift). Perform the same test on a vehicle with a crank trigger and you'll get opposite results, the cam timing will drift and jitter, but the crank will be rock solid. |
Originally Posted by DammitBeavis
(Post 348740)
Either way, I'm beginning to feel that it might all be academic. When I began I was told I was using the ideal setup, now that I start to see the holes in the theory, I have to wonder why this stuff has held up so well.
Originally Posted by 18psi
(Post 348627)
total ms noob here, let me get this straight: ms2 will work with the nb crank wheel/sensor and its possible to get it working without installing the n/a wheel and cas?
If that is correct, why are so many members like cjernigan and patsmx5 using the cas or some other sensor besides the stock nb one? Most of the people running something else either did it before I came along and told everyone what I tried, or they heard from other people it couldn't be done. I'm looking for someone with a bit of electronics skill (can use a voltmeter, solder, etc) to help me test a board - it's a plug-and-play board for '99 + cars. Yes the MS-II code sucks, so does MS-I, but you will get better timing out of the II and if you do it right you don't have to cut any harnesses, just plug in a board to the OEM connector, and don't have to buy any sensors, either, though a GM AIT is highly recommended.
Originally Posted by DammitBeavis
(Post 348743)
If you want to see it yourself, set your timing to a fixed 10deg and grab a timing light. Point it at the crank and watch the timing drift and scatter at different speeds. Then point the light at the cam gear and you'll note that it's rock steady (there will still be a bit of scatter from the slack in the drive gear, but no drift). Perform the same test on a vehicle with a crank trigger and you'll get opposite results, the cam timing will drift and jitter, but the crank will be rock solid.
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Originally Posted by AbeFM
(Post 348784)
There goes all my arguments. I was going to point out delays in the sensors, and then I was going to say watch cam phase in the logs... But that should work, so if you've done that and that's what you see, I agree. Although I doubt camshaft momentum has hardly anything to do with it, I'm sure fighting the valves is much, much more significant a force. Then again, they should "average out"?
My experiment was with two similar but different engines, not one with two different setups. After being told that it was true, seeing that evidence was enough to convince me. However it was hardly scientifically rigorous and there are quite a few variables. Maybe my timing belt was weak, or tensioned wong. I'm actually planning to convert the DSM to crank trigger, but if I'm wrong and wasting my time then I'd like to know before I go through the trouble. |
There's a miata trigger right there on the wheel, seriously, don't bother. If the autotronic won't see the sensor, it's $1.37 in parts to make something which will spit out something clean. I even have half assed plans for a board you could steal and make but I wouldn't bother with them.
If the computer seriously has issues with the 4 teeth, cut two off. I think some people have done this on the MS-I |
Originally Posted by AbeFM
(Post 348818)
There's a miata trigger right there on the wheel, seriously, don't bother. If the autotronic won't see the sensor, it's $1.37 in parts to make something which will spit out something clean. I even have half assed plans for a board you could steal and make but I wouldn't bother with them.
If the computer seriously has issues with the 4 teeth, cut two off. I think some people have done this on the MS-I My miata (autocross car) has been working fine off the OEM NB crank triggers on an Autronic standalone for a couple years now. I converted it from a TEC-II with a 60-2 crank trigger to an Autronic SM4 in late 2006. I chucked the 60-2 wheel in the conversion, ground off two of the OEM crank teeth at ~10*BTDC and also ground off the double teeth on the intake cam gear so that there is only one sync pulse. There are no problems there, works great and always has. My CAS experience has been with a 4G63 in my DSM (rallycross car) which is in the same configuration and works exactly the same way. Even the CAS pattern is the same. It's using an Autronic SMC standalone but I was thinking about converting it to a crank trigger system using leftover miata parts. That's the engine I experienced the CAS timing drift on. I was looking for confirmation that somebody else got the same test results in the crank vs. CAS trigger experiment so that I could confirm the conversion on my DSM will result in a more consistent ignition system. The reason I was messing with the miata triggers this time around are not really related to this thread at all, but I ran across the quotes I posted from Ian while researching the trigger patterns. My intention with the miata (if anybody cares) is to combine the cyl and sync pulses into one signal wire to free up my sync input for use as a wheel speed input for traction control. |
Ah! I thought you were saying you wanted to have more accuracy on the engine speed to judge wheel slippage based on that, which I thought was insane. :-P
I can check the ... shoot, no timing light! But I have seen my own cam bounce around, and my friend's crank bounce around, and I'm crank timed while he's cam. Not a great data point, I'm afraid. I don't have a scope at home right now, so I can't watch this for you.Joe had both set ups on his car, but I don't know if he can go back and forth in software. BTW, the FreeEMS (ok, so it's not done yet) has somewhere around 80 inputs, so there's less worry about running out of pins. :-) |
I have some spare inputs left, however the computer only has 5 'high speed' inputs capable of reading and interpreting toothed wheels. 2 for cam/crank, 1 for vehicle speed, and 2 for variable valve timing control. I want to use 4 of them for traction control by tapping into the ABS sensors, so that only leaves one for reading engine position. I could probably use 3 with one for each front wheel, then one on the speed sensor in the gearbox. The speed sensor SHOULD be an average of both rear wheels, but I'd like to have the option to try it both ways.
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Curious, why would you need more inputs for variable valve timing? I guess if each cam was independent you would need a third channel, otherwise the cam and crank would have all the info you need. And I bet you could do the speedometer through a divider to get vehicle speed and still have reasonably accuracy.
Still, it seems like a fun project. BTW, traction control reading the front wheels? You're not talking ABS, right? If the front starts to slip, what do you do with the rear to maintain traction? :-) |
I've not messed with the variable cam controls, but my guess is that the single pulse sync signal is not comprehensive enough for cam control feedback, and probably should be on the part of the cam gear that isn't moving about all the time. It is capable of controlling two cams independently if the need arises, hence two high speed feedback signals.
The traction control must read the front wheels in order to know ground speed so that it can determine the slip on the driven wheels. If it were a drag car then I could just read one front wheel and the speedo gear. But since I want traction control to work while turning sharply I'll need more information. I've seen plans for a twin mercury switch circuit that will change which front wheel it's reading from depending on which way the car is turning, but I was hoping for something more elegant. With the strong LSD I'm using, the speed sensor in the gearbox should usually indicate an average of the two driven wheels. However I know that I do occasionally lift an inside rear wheel off the ground, and it would be very cool to be able to log this and see if I would benefit from tightening up the diff or softening the rear sway. I'd like to be able to continue pouring on the power as long as the wheel with the weight on it is still doing some work reguardless of how much faster the one in the air is spinning. Another benefit of having a wheelspin parameter is that instead of setting a separate boost curve for each gear (which is fairly surface dependent), I can simply tell it to run full boost and it'll cut back the power automatically at say 15% wheelspin. |
Originally Posted by DammitBeavis
(Post 348743)
At a steady RPM, any prediction algorithms would be doing nothing but a little averaging.
The tests aren't surprising really, but it is interesting to hear it. When I did the timing light test I could floor it in neutral and it would be rock solid and barely move. This is ms2 with 36-1 wheel on the crank. Fred. |
Just thought I'd share this since I was skeptical if it would work. I needed to move my sync signal to within 90 crank degrees after a crank pulse in order to make it work with my new setup. I used the least scientific and most half-assed method of doing it and it worked out great.
I was aiming for ~45* after the crank pulse (precision wasn't necessary), so I simply marked a point on the crank signal wheel 1/4 of the way between the teeth with a tape measure and lined the mark up with the sensor. I removed the cam sensor and stuck a sharpie marker in to make a dot as centered as possible on the cam gear. Then I removed the cam gear, measured the height of the existing nubs, and ground them all smooth. Next I drilled a hole where the sharpie mark was and tapped it for a M6 bolt which was approximately the same width as the factory nubs. I then put the bolt in from the back, and used a dremel to shape the tip that stuck through to the approximate dimensions of the other mark. It fired right up and worked. In fact, it worked so well that the sharpie method got me to ~46*, so I was only 1* off my target! :bowrofl: |
Originally Posted by AbeFM
(Post 349000)
Joe had both set ups on his car, but I don't know if he can go back and forth in software.
I did, however, perform a back-to-back comparison of timing stability on the CAS and on the crankwheel. This was done by locking the timing to 10°BTDC in software, and opening the throttle by hand while illuminating the reference mark on the crank pulley with a timing light. With the CAS in control, I observed greater than 5° of jitter at a constant RPM of... shoot, I think it was ~5,000 RPM or so. (been a while.) I then switched to crank-trigger mode, and observed a jitter of ~1° at the same RPM. The timing belt, at that point, was about 2 years old (roughly 10,000 miles) and was properly adjusted. I'd imagine that an engine with an older (and presumably looser) timing belt would yield even poorer timing stability when triggering off the cam. |
Originally Posted by Joe Perez
(Post 351734)
At the time I did the conversion, I was able to switch back and forth between the 36-1 crankwheel and the CAS by moving a jumper external to the MS and changing the software settings. I can't do that anymore, since my CAS is presently taking up space in a landfill somewhere. (Or perhaps, since I threw it away while in CA, it was shredded, mechanically sorted, and then recycled. Who knows, maybe in a year or two I'll wind up drinking out of a can that used to be my CAS.)
I did, however, perform a back-to-back comparison of timing stability on the CAS and on the crankwheel. This was done by locking the timing to 10°BTDC in software, and opening the throttle by hand while illuminating the reference mark on the crank pulley with a timing light. With the CAS in control, I observed greater than 5° of jitter at a constant RPM of... shoot, I think it was ~5,000 RPM or so. (been a while.) I then switched to crank-trigger mode, and observed a jitter of ~1° at the same RPM. The timing belt, at that point, was about 2 years old (roughly 10,000 miles) and was properly adjusted. I'd imagine that an engine with an older (and presumably looser) timing belt would yield even poorer timing stability when triggering off the cam. |
Originally Posted by Joe Perez
(Post 351734)
I did, however, perform a back-to-back comparison of timing stability on the CAS and on the crankwheel. This was done by locking the timing to 10°BTDC in software, and opening the throttle by hand while illuminating the reference mark on the crank pulley with a timing light. With the CAS in control, I observed greater than 5° of jitter at a constant RPM of... shoot, I think it was ~5,000 RPM or so. (been a while.) I then switched to crank-trigger mode, and observed a jitter of ~1° at the same RPM.
Originally Posted by rb26dett
(Post 351700)
The tests aren't surprising really, but it is interesting to hear it. When I did the timing light test I could floor it in neutral and it would be rock solid and barely move. This is ms2 with 36-1 wheel on the crank.
Fred.
Originally Posted by DammitBeavis
(Post 351714)
I used the least scientific and most half-assed method of doing it and it worked out great.
http://abefm.smugmug.com/photos/240509038_LcYFK-M.jpg I just cut a piece of computer case out, put some holes in it, and moved the sensor some degrees from where it normally lived. It didn't fix my problem, though it did exactly what it should do, and hence pointed me to the read issue which I later fixed. :-) |
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