DIYautotune's CAS replacement wheel
 

Has anyone tried the DIYautotunes new cas wheel in place of the stock 4+2 cas wheel?

I bought one, then found out both my CASs were not optical even though one of the covers suggested it should be optical.

Interested in selling it?
I know for sure mine are optical since I've opened both mine.

sure, send me a pm to remind me tomorrow, I'll give you a good deal on it.

Still triggered off the camshaft, so what's the benefit?

I would think a higher resolution if the sensor can handle the extra slots without issues.
so more percise understanding of where the crank position is.

It's supossed to provide more resolution since there's, what, 12 teeth instead of 4.

edit: what tech said.

More resolution, but will you actually gain anything from it? you'll still suffer from spark jitter, possibly worse due to the amount of smoothing less resolution can give.

Personally I would be hoping to see less spark scatter, but I won't know for sure until I get my hands on one and find out if its possible to use.
I figured with knowing better crank position there would be less timing error

Did you want it? I think I sent you a pm

I still don't see the point. The belt has several degrees of slop and is what causes the timing error. I doubt you'll see any measureable difference from going to a 12 disc.
Still, I hope I'm wrong and am very interested in seeing before and after measurements!

All i know is, that when I went from MSII to MSIII, the resolution was so much better, that i was barely able to first idle the car; it turned out I forgot to tightening my timing belt a few months before over winter and that the MSIII, all things being equal, was more accurate at reading the signals and the fuel/spark timings were random and off.

So I'm assuming that being able to get a more accurate picture of the crank angles would just make your fueling a touch more efficient.

Yes I want it, got to get money moved over, I'll send you payment today.

on ms2 I noticed a bunch of scatter even at idle compared to my stock ecu which was rock solid. I think its also a partial software issue.

I just ordered one, so we will see. Pretty good price and nothing to loose really. It should give way better resolution in theory.

Nice looking rx7s do you have any links to info about them?

That particular wheel was designed to replace an oddball Nissan 24-1-1 wheel for which native software support was not available in the MS1 and MS2 code.

In other words, the design intent was not to improve accuracy on 4G63 cars, it was to allow 24-1-1 cars, which could not previously use a Megasquirt without custom-fabricating a crank trigger, to do so.


If you want better spark accuracy, buy TSE's 12 tooth crankwheel.

Its a 360 hole optical wheel that the diy cas wheel replaces that would be better all together if the older MS's supported it.
https://www.miataturbo.net/attachmen...ine=1324493699

360 teeth will just waste processor cycles reading them all, pointless.

The TEC lineup as one of the most accurate ignition systems available and it only uses 60 teeth, tell me why more would help?

Well the one in the middle was crashed a couple of years back and we rebuilt it. I will post some picture and info in the build section soon. The one on the left (1st gen) is getting a restoration with a BP engine and big turbo. I will add info on that in the same build thread. This is all if I have time!

If I use that crank trigger, can I still use the CAM part of the old CAS for my cam trigger input or do I need a 99 cam sensor?

^This.

The MS2 might be able to handle it, but with a 360 tooth wheel, the poor little MS1 would probably crash. At high RPMs, I doubt it would even be able to handle the primary interrupts fast enough, much less actually run the engine. For comparison, an engine with a 360t wheel running at 7,000 RPM would put as much interrupt workload on the CPU as an engine with a EDIS-style wheel (36-1) running at 72,000 RPM.


More to the point, a 360t wheel mounted on the end of the camshaft will still have more steady-state scatter as a two-tooth wheel mounted to the crankshaft.

Much more eloquently put than me as usual Joe :)

Nice maths too BTW, puts it into perspective how much load a 360 tooth wheel would put on an ECU, 72,000 rpm!!

Nissan used dedicated hardware to handle the 360 slit ring. Neither the MS1 nor the MS2 can really use that set of slits properly unless someone tried to clone the external counter circuit Nissan used and write code to make it work.

The MS3 is a different case - it's possible to program the X-gate to take the place of the stuff Nissan used to run this wheel.

Maybe if you held RPM steady. With rapidly changing RPM, the higher tooth count wheel would be better (assuming (1)your processor is up to the task. so far, the MS3 is doing well with 360 tooth testing; (2) you don't have an abnormal level of slop in your timing gear).

Agreed, assuming that the ECU in question is capable of predictive estimation to select the tooth most appropriate to start the timer (MS2/3), which is why I called for "steady state". And even at this, you're only compensating for spark drift based on error in the timer setting relative to acceleration of the crankshaft. This drift, while undesirable, is at least predictable and can be compensated for in dyno tuning, assuming that one is tuning with an inertial dyno rather than a steady-state dyno.

Any slop in the cam belt system as a whole (which I measured at nearly +/-5° steady-state in my engine with a new timing belt) will remain unaffected. Ergo, periods of low delta-RPM and high load (eg: boost in 4th or 5th gear) will suffer from equivalent scatter regardless of toothcount.

Is there a 1.6 bolt-on 36-1 cranck wheel available?

There is at least one that I am aware of. Took a while to fabricate, and it's currently installed on a '92 somewhere up in Michigan.

Success, ms2extra running my 1.6 miata motor with the diyautotune cas shutter wheel.
Tested in both batch inner ring and with the outer and inner ring. Working on both. Spark scatter is a lot less now at idle.

If it fits on the front of the crank there is no way in hell it will fit with AWR swaybar mounts.
https://www.miataturbo.net/attachmen...ine=1326144002

Good to know! You mentioned in your other post that is seems to be way thinner than the factory one. Did you have any problems with that?

I'm not sure why its so think, my guess is for laser cutting it out. It being so thin makes it very flimsy compared to the stock disc. you can easily bend it in different ways where the stock one you couldn't bend it without getting it stuck in the shape you bent it to. Also since its so thing it likes to bow instead of stay flat which leads to it rubbing aganist the black plastic of the sensor pickup housing in the CAS.

It maybe the material as well, I didn't check if it was metal or alu but if a tad thicker wheel keeps it from bending like it does I would suggest diy to go for it if costs don't go up drasticly as well if it can still be laser cut.

is there a link to the diyautotune CAS wheel? I couldnt find it on their site.

thank you

1.6 93=< do drive the tach of the coils but having a different cam\crank setup has no bearing on the output of tach signal.
And if you do convert to seq spark you would have to get tach input from a different source as you would change out your coils as well more than likely.

on the 1.8s I don't know wheres its driven from.

and yes cut off one if you want the TSE 12 tooth to be a 12-1

Besides that if you are going to convert to this new wheel I take it you are running a standalone so you might want to consult with the manual and see if it can output a tach signal

1.8 is driven from 2 sources depending on year.

Up to 1995.5 it's driven from the coils, post that'd date the ECU drives the tacho

Anyways going back to the thread I used first 345 tigger offset to get my engine to fire up. No go just loud back fires. Read up something so I started advancing timing got to 200 where it fired and ran like a weed wacker. Finally end up at 135 trigger offset with 18 degrees of timing at idle.

Just once, but apparently I didn't put two and two together.
I don't understand why. Why am I required to run a 12-1 CKP if I have a single-tooth CMP? It seems logical to me that I can use a single tooth CMP to indicate position.
Why not run the 12-tooth wheel for less scatter?
Got it.
Thanks.

I'm going to make a seperate thread for my problems, I can't be the only one who's this dense...well, maybe I can.

Running a 12T wheel on an NB, you have two basic options:

1: Cut off one tooth (thus creating a 12-1 wheel) and run with no cam signal at all. This is essentially the same as my old setup with the 36-1 crankwheel.

You will be limited to batch injection and ignition in this mode, as you don't have an absolute cycle reference. In other words, without a cam signal, the ECU can't tell whether the #1 cylinder is at TDC on the exhaust/intake cycle or the compression/ignition cycle. And, of course, no VVT.


2: Leave all of the teeth in place, and modify the intake cam pulley (for '99-'00) or the intake cam itself (for '01-'05) to remove two of the three teeth, so that you have one pulse per cam revolution on the second sensor. This will enable you to run fully sequential spark and fuel, however this configuration will most likely not allow closed-loop VVT to work, as the crank teeth are too closely spaced, and the cam pulses will therefore cross over crank pulses as the cam advances.


IN THEORY you should be able to run a 12T crankwheel with a stock NB-style cam signal, however there is no SOFTWARE SUPPORT for such a configuration at present. Configuring the ECU to understand such a signal is a more complex task than can be achieved with the "generic wheel" configuration table, and it would thus require a custom configuration within the software itself, such as the ones which were done to support Neon/420A, Subaru 6/7, Mitsu 4G63 or '99+ Miata sensor pairings in the MS2. (In other words, the ones where you just select "99+ Miata" from a drop-down window, rather than manually keying in all the tooth data.)


So, long story short: The 12T wheel is an excellent upgrade for NA owners looking to eliminate their dependence on the CAS, and is a moderate upgrade for '99-'00 owners looking to slightly improve the accuracy of the spark prediction. For owners of VVT engines, however, there are some serious disadvantages which outweigh any potential benefits.


On '90-'93 engines, there is an igniter seperate from the coilpack, and this generates the signal to drive the tachometer in the instrument cluster. On '94-'95.5 engines, the igniter is integrated into the coils, and the tachometer signal is generated here. On '95.5 and later engines, the igniter is still integrated into the coils, however the tach signal is produced by the ECU.


If you convert to sequential spark, then by definition you are not using the stock ignition coils.

If you have a '95.5 or later car, this does not matter, as your tach signal was not in any way related to the ignition system to begin with. The ECU will continue to generate the tach signal just as it did before.

If you have a '90-'95.5 car, you will need to run a new wire from the ECU to the wire that drives the tachometer in the instrument cluster, and have the ECU start generating the tach signal just like it would in a later car.

In either case, it does not matter how many teeth are on the wheel, or whether you are using one wheel or two, or whether you are using two coils or four. The ECU simply generates one pulse on the tachometer output pin for every ignition event.


Each of your two ignition coils has one tachometer output pin which is driven by the coil's internal igniter. These two outputs are wired in parallel to the tachometer. Every time an ignition coil fires, it generates a pulse on the tach output pin. The summing together these two lines means that the tachometer sees one pulse every time either coil fires.



Right here, good buddy. :D

http://img72.imageshack.us/img72/5562/121gu.png
By techsalvager at 2012-01-17
http://img440.imageshack.us/img440/8666/4g63cas.png
By techsalvager at 2012-01-17

Timing error%
diy's n top
stock on bottom

Interesting you can see its in the same area with GVE the same nearly but its way leaner on the other one compared to current which is richer. Guess its the map sensor change causing this.