Need some help from electronics geeks
 

I am working on installing a fresh S5 engine in my '86 GXL and have been pondering my options for controlling the VDI and 5/6 ports. I was planning on using a MSD RPM switch, but found this thread in the archives: https://www.rx7club.com/2nd-gen-archive-72/how-diy-rpm-switch-6th-ports-vdi-233381/

I have been looking at it trying to figure it out and am getting there, but my knowledge of circuits is pretty limited. I tried sending a message to the original poster, but haven't heard anything yet which isn't surprising considering the thread is from 2003. Below is the schematic he posted.

https://www.rx7club.com/attachment.p...1&d=1196984006

Pic of completed board:
http://forum.teamfc3s.org/attachment...8&d=1066659883

One of my questions is where the schematic has a 50k resistor to the right of the IC, it says "Set Rev Limit". As you can see on the built board, there is a pot on the board. Can I assume that means I should use a 50k pot?

This is my parts list so far based on the schematic:
LM2917 IC
Relay
15v Zener diode
1N914/1N4148 diode
1N4001 diode
2SD1683 transistor
10k resistor (x2)
22k resistor
470 resistor
100k resistor
50k resistor
50k pot?
430 resistor
15k resistor
.02u cap
.022u cap
1u cap

I would like to make a few of these and post up updated info on how to build these units (step by step instructions, parts list, etc.) to help out other people that may be interested in building one of these.

Yes, the 50K resistor is a pot as shown on the schematic (resistor symbol with arrow pointing to it).

This may help:
http://www.aaroncake.net/electronics/schem.htm

Anything else you need? :)

Thanks man, I appreciate it. Does my "shopping list" look complete?

Get an Rtek 2.1 and use the rpm switch capability that is built in. It will be a lot simpler, and will also give you the ability to tune fuel and timing. You can change cranking fuel to prevent floods as well.

I'd even be tempted to wire up an s5 ECU with Rtek 2.1 and use OEM s5 solenoids to switch the aux ports and VDI, just like stock. The s5 RTEK already lets you adjust the aux ports and VDI rpms.

I have looked into the Rtek, but it is wayyy overkill for my current setup. This is a stock S5 engine going into my S4 and I am just looking for a cheap way to control the solenoids. The Rtek may be a possibility during "stage 2" once I get my second ending ported and rebuilt. For now, I just want to get the car on the road as soon as I can.

http://www.jaycar.com.au/productView...H&form=KEYWORD

And or SUMMITRACING sells a similar unit for about the same price but it's already built....with instructions.

I have seen that unit, but I like the fact that I can build the switch in my original post for $10-15 per box instead of $38. Not much money, but still money that could be spent on other parts. Plus, I want to be able to say that I built the circuits myself.

One of your emissions solenoid's rats nest colored wire connectors activate at 3500 rpms I believe. I took a solenoid and plugged it into that connector for an air pump so that at 3500 rpms it would trip the solenoid and activate the air pump that turned the VDI and in my case, the secondary ports too. Worked like a charm and its funny, I could even feel the power change when the air pump kicked on and activated everything at the same time. Its pretty simple. However its not the same at 3500rpms activating the secondary ports, and 5000 activating the VDI. Suppose you could run an emissions vac/air solenoid in between the air pump hose to the VDI that activates at 5K rpms via an rpm switch like the one you're building and then everything would work as stock.

JAYCAR is much more versitile. And you build it yourself from parts supplied to you from them.