NA Bolt in trigger wheel upgrade
 

http://www.diyautotune.com/catalog/i...w_sr20_med.jpg

Bolt in upgrade trigger wheel for the NA. We originally designed these for KA24 and SR20 Nissans, but wouldn't you know that the Nissan CAS and Miata CAS use the same size shutter wheel.

This won't magically remove timing error caused by belt stretch or cam twist under load, but it will provide for better resolution than the factory wheel can. Compatible with MegaSquirt or any other programmable ECU. It's definitely not going to work with your stock ECU. The CKP ring can be set up as a 12-1 wheel at crank speed, and will allow for batch fuel and wasted spark ignition. This eliminates the need for a 2nd tach input if you plan to run batch. The CMP wheel has 1 tooth to enable sequential fuel and/or ignition as desired.

http://www.diyautotune.com/catalog/n...4de-p-472.html

Note that the CKP ring is the *inner* ring on this wheel, and the CMP wheel is on the outer ring. Please wire your harness accordingly.

There's really nothing to say here apart from :bigtu:

As a speculative observation, the combination of this wheel plus the stock '96-'97 crankwheel and sensor (with the removal of two of the wheel teeth) would seem to allow full sequential operation on any 1.8 NA, plus the added benefit of decreased timing error from the elimination of belt stretch.

Very cool stuff, Ben.

Thanks Joe.

Interesting point, but I'm not sure if a 2 tooth crank wheel would actually be more precise than a 12 tooth cam wheel. Could make for an interesting experiment.

So what exactly is needed for me to switch from my current setup (1.6 car with transplanted 1.8)? I don't have a crank sensor, I'm running a diypnp, with sequential injection, batch fire for spark.

It drops into your current CAS. I'm pretty sure the stock Miata CAS has CKP on the outside and CMP on the inside, so you'll need to switch those 2 wires on your adapter board. Then change your tach input in software from 4G63 to toothed wheel. Your trigger wheel settings are dual wheel, 12 tooth main wheel at crank speed with 1 missing tooth.

If you're not running sequential, you can set the trigger wheel for single wheel with missing tooth instead of dual wheel. The CMP ring is only needed for sequential.

Methinks...
2 tooth crank wheel should be more accurate at constant RPM.
12 tooth cam wheel *may* be more accurate during RPM transients.

I may be missing something, but that doesn't look like it will bolt into this:

http://forum.miata.net/vb/showthread...=387335&page=2

I know their are actually 2 different NA CAS's, one magnetic and one optical, but I think they both use the style of 'wheels'.

So technically I could just switch two wires at the CAS wiring harness? Do you happen to know which wire is which?

Let's get this straight. I'm about to order one. It seems like a pretty simple upgrade. Remove CAS, insert wheel, reinstall CAS, switch two wires at CAS harness, change tunerstudio settings.

I assume that setting base timing is still the same: lock at 10 degrees and rotate CAS until on target?

This thread has info on what wire is what, but below is the relevant wiring picture.

http://i28.tinypic.com/2hpmyk7.jpg

Quick research shows the 1.6 CAS is optical, and thus POTENTIALLY compatible with this. I'm still searching for pictures... I think the 1.8 is the wheel w/ the arms and won't work.

EDIT:
from a thread on m.net:
"the earlier CAS is an optical unit that reads holes punched in a disk while the later unit is magnetic based."

I've got one of each, if yall want to ship me a disk I'll certainly check if it fits in a 1.6 cas :)

Edit2:
from DSM thread ( http://forums.turbobricks.com/showthread.php?t=224740 )
I bet the sensors are the 'same deal', and since I have 2, I can tell you that the 1.6 looks like the optical type from this page (from the outside anyway)... and the 1.8 looks like the 'hall effect' version from that page (based on the back covers, 1.8 has the convex bump on it) I can also tell you 100% that they swap back and forth (I've run my 1.8 car with the 1.6 CAS in it)

So, does this make 1.6 CAS's more valuable to us? :) I've got a trackspeed wheel I'm going to wire up at some point so its kinda moot for me.

No, the two styles of Miata CAS are completely different internally. The hall-effect version uses two plates with raised arms which are perpendicular to the axis of the baseplate.

This plate would not be compatible with a hall-effect style CAS.




I only have a single datapoint here, but I do know that the CAS which was installed in my '92 when I bought it was of the hall-effect style. I don't know with certainty whether it was the original unit, however the vehicle had less than 50,000 miles on it when I purchased it and there was little evidence of any maintenance having ever been performed on it, so I suspect that it was the original unit.

Odd, maybe they interchanged them willy nilly? Is it possible there was a TSB at some point and mazda replaced optical ones with hall units? The hall units are thought to be more reliable as they don't have LEDs that can go bad. (rare we all know, but it can happen)
My brothers 93 had the optical CAS in it (the spare '1.6 cas' that I have)

I posted once how you can tell the difference between the two.

I will post a picture of a 1.6 CAS opened in a few minutes
They use a metal discs with slits cut into them

quoting myself: the optical ones have a flat back, with a slight recess, the magnetic ones have a domed back

Then my '90 also has a mag sensor.

Of course, God only knows what the service history is on that vehicle. The engine is a shortnose, but I've absolutely no idea whether it's original.

This is correct. You will need a "square" CAS. The domed CAS is different. I was going to install our new wheel in one for you guys and grab pictures, but wasn't able to on Friday.

This is what the inside of the optical CAS looks like with stock shutter wheel.

http://fixjunk.com/solomiata/solomiata2/Miata16CAS.jpg

This is the later hall effect CAS. It has a domed back. Our shutter wheel is not compatible.
http://fixjunk.com/solomiata/solomiata2/Miata18CAS2.jpg

I've got one of each. yay.

What are the odds, with the proper screwdriver, of putting one of these on while the CAS is in the car.?

Not a chance.

What does a 1991 have?