I understand now. I did not understand before when I was flustered. I have the harness CAS wires coming in on pin 2,(spr1)3,(spr2)4,24 and the Zeal board was running to IAC1A and IAC1B. The zeal needs to be hooked up to SPR1 and SPR2.

So I assume, SPR1 (green wire) is going to VR2+ on the zeal board, while SPR2 (black/white wire) goes to VR2-

After that I just need to re-solder the pins for the ignition output and I will have it all correct.

I think a lot clearer in the morning apparently. Thanks for your support guys!

 

This discussion has helped my confusion a lot too. If you gurus don't mind I have a few ?s I didn't see covered though:

From the sound of it, if I use the zeal, I'll have 4 circuits for CAS input but only use 2? What is the downside if I decide not to solder in the circuit for the VR1 on the Zeal and Hall/optical on the MS3?

Aaron sez to ise resistors for the GM IAC & CLT sensors, but can't I use the stock sensors & that "easytherm" app to adjust the values? I also don't get why we use all 3 LEDs for trigger, can one be wired for a fault code?

This one is particularly embarrassing, but what's a twin-scroll solenoid? I thought the twin scroll setup had to do with the split inlet and exducer geometry.

Lastly I was hoping to employ some kind of knock detection circuit. Do I need to solder that in? Can I use the factory knock sensor, or would it be useless at this point?

Thanks for all the great info.

 

I haven't used the Zeal before as I'm a bit of a traditionalist and just build the VR circuit, but from memory, the Zeal has two VR circuits. So you will have the one on the V3/3.57 board, and two on the Zeal. You'd use the Zeal circuit for the two tooth wheel and ignore the other VR on the Zeal.

I don't think you need Easytherm with the MS2. But why use the old, crusty and expensive OEM sensors when you can pick up the GM sensors with pigtail harness plugs for $15 at an auto parts store? And not have to bother calibrating them?

The LEDs are used because they are a convenient output source. Three lines are needed: leading trigger, trailing trigger, and trailing toggle.

The twin scroll is a valved turbine housing on the S4s. At low RPMs, only one scroll is open and it is set up to hit the turbine wheel at a very sharp angle, spooling it quickly. Then at 2700 RPM, the second scroll is opened via a flapper door moved by a vacuum actuator. This second scroll hits the turbine wheel at the edge, better for flow and higher RPM operation.

To be honest, the stock knock sensor is so old that it's not very useful. As I recall (could be wrong here) the sensor is only really adequate up to about 2000 or 2500 RPM. If you are going to do knock detection then use a more modern sensor. However it seems to be of limited use on the rotary. If you tune to appropriate AFRs and timing, then knock isn't a big concern anyway.