miatamike203

So as most of you know I'm doing a sr20 swap in my miata and I would love to run ms on it also. After talking to Matt bit he said the cas on the sr20 won't work with the ms. So now I'm wondering could I just do a crank trigger wheel and not use the cas?

Joe Perez

iTrader: (8)

I can't imagine why not. With a generic crank trigger wheel (such as a 36-1) you can run a megasquirt on damn near anything that has spark plugs, fuel injectors, and an even number of cylinders.

I'm not all that familiar with the SR20 engine. Is it one of those weirdos that runs a CAS pattern giving something like 473 pulses per revolution on CKP?

ianferrell

Jmscortina has been working on some nissan cas stuff for ms3, you might wanna read about that.

http://www.msextra.com/doc/ms3/nissancas.html

miatamike203

Matt was telling me there working on some firmware to make the cas work and I'm not sure why the cas don't work. I was also told people swap the wheels for the one out of the dsm.

y8s

iTrader: (8)

can the nissan cas be modified to produce a known sync pulse?

miatamike203

Here is what Matt said to me on mx5atlanta.com

There currently isn't any firmware for the stock CAS, although there's some experimental code for the MS3 that needs to be tested out. Most installs have used an AEM or DSM trigger disc in the stock CAS

Joe Perez

iTrader: (8)

I finally found an image of one, and I'd have to say that the answer sounds like a yes.

Here's the stocker:



360 pulses per revolution on the main channel. Does that poor ECU have time to do anything other than receive primary interrupts?

I see two possible courses of action. You could knock out the majority of the holes in the outer ring, and apply a patch over others, to bring it down to a more reasonable pattern. Four evenly-spaced slots would suffice. Patch over the three small slots on the inner ring and you have a nice, easy 4+1 dual-output CAS.

Might now be much space available to do the patching, though. The optical elements have got to be pretty closely spaced if they're reliably reading that outer pattern.

Or you could do what some enterprising enthusiasts have done and get a new trigger plate. 24+1 seems to be popular, judging from a quick google search:







It would appear that AEM maketh one, too:



As does VEMS:




This is what it would sound like if If Leon Redbone Suffered a Major Head Injury.

miatamike203

Joe you must have the holy Grail of ems info. This is great info you just sent me.

I must ask what did you type into google.

Joe Perez

iTrader: (8)

http://lmgtfy.com/?q=leon+redbone+head+injury&l=1

miatamike203

Thanks Joe I never knew how to use google, just amazing lol. Anyways I am liking this ideal you have here.


" You could knock out the majority of the holes in the outer ring, and apply a patch over others, to bring it down to a more reasonable pattern. Four evenly-spaced slots would suffice. Patch over the three small slots on the inner ring and you have a nice, easy 4+1 dual-output CAS." Joe

So all I do is make 4 good size slots that are the same size and evenly spaced to make it work?

miatamike203

Thinking this might help.

Joe Perez

iTrader: (8)

Hehe.

Actually, I just went to google images and typed in SR20 CAS. The first page was filled with images of non-standard CAS wheels, so I'm guessing this is a pretty common issue.


That, and also block off all but one of the four CMP slots. If it were my car, I'd also want to add some material between gaps in the outer ring, to make sure that the CPU has time to detect the transition to "off" before the next transition to "on". Whether this is a real problem or just an academic issue I can't say.

The only other concern is how to go about blocking the slots. From the image miatamike203 posted, you can get a feel for how tight the fit is in the gap between the LED and the phototransisor. Anything that adds significant thickness to the disc may prevent it from passing through this channel. You're not going to just glob some JB-weld on there. Foil tape might work.

miatamike203

I was thinking of filling the holes with bondo then sanding down the high spots.

miatamike203

Oh other question is what hole out of the 4 holes should I keep? I'm sorry this is the point where I'm lost on everything and how it would be set on ms.

miatamike203

After looking at the diy KA wright up it looks like the ka uses the same cas as the sr.

http://www.diyautotune.com/tech_arti...ssan_240sx.htm

miatamike203

I also could do what aem did with the 24+1 by taking out 15 slots then skipping 15 slots. It would give me the same out comes as aem has. Just would need to fill the 15 slots I left in place. Should work right?

240_to_miata

iTrader: (2)

Wish I saw this thread earlier...I probably could have helped you out.
You can change the wheels out pretty easily as people mentioned. We ran MS on my friends older VE30E Maxima that had a similar setup. The inner and outer holes use different sensors so you can do pretty much whatever you want when it comes to a trigger wheel.

I was about to start getting into MS right before I crashed my second 240.

miatamike203

So after spending a good amount of time looking into running ms on my sr I decided to go with the crank trigger wheel. I do have a few questions tho. What is the best cps to use? Next is should I set up the ms2 for edis or dis? The sr uses 4 cops and an ignitor so I'm guessing dis for wastespark? Then I'll just need to figure out the needed coil dwell.

Joe Perez

iTrader: (8)

Maybe this is just my ignorance showing through, but that article doesn't make any sense to me.

Basically, they are saying to leave the wheel completely unmodified, ignore the outer ring completely, and trigger on the trailing edges of the inner ring (which are evenly spaced.)

In that configuration, the only thing that the ECU would be able to infer from any given pulse is that "something is ready to happen." In other words, it has no way of distinguishing one cylinder from another. Forget about wasted spark, you'd have to use a distributor.

Did these engine have both distributors AND cam-angle sensors?



That's basically what I'm describing. You could go all the way down to four slots if you wanted to, but doing the +15-15 routine and winding up with a 24 hole disc (equivalent to a 12 tooth crankwheel) would be better.

You still would need to do the same routine on the inner ring, leaving only one hole intact, as you need some kind of reference to judge absolute cam position.

Well, actually I take that back. Since this wheel is turning at cam speed, you could do a "missing" tooth and still be able to run sequential, but I think it'd be better to run twin-signal. Less ambiguous.



Ok, wait. Are you the same guy who started this thread?

A crankwheel, if properly done, is always superior. More precise, since even timing chains have some slop. If you go the crankwheel route, you will still need a 1-pulse-per-rev cam reference if you want to run full sequential. (You could still wire for semi-sequential fuel and wasted-spark ignition if you needed to, but the cam sensor will allow you to avoid this.)

Avoid EDIS. It will give your dog herpes.

The best CPS to use is the one that fits. Here is one example of a completely custom crankwheel setup: https://www.miataturbo.net/megasquirt-18/wheel-timing-success-last-20241/ (Other have done theirs differently. I pass no judgement here. I will add that on mine, it took quite a bit of fiddling to get it all just right.)

miatamike203

Thanks for the link very helpful.