Or, does anybody have a pinout / schematic of our ECU. Tuners... rpm or tach signal ?

 

GMS and the others who “tune” ECU’s with a different rpm cutoff than came from the factory and also some have different methods of cutoff (one uses cutting fuel most use cutting ignition) so some control is possible that’s rpm related thru the ecu so maybe check w them.
If you don’t need exact off on action would a vacuum triggered switch work?

 

Only sure fire way I’m aware of on modern cars like these is through the OBDII or CAN bus - RPM can be read from that port digitally there and you can use a raspberry pi or the like to flip a switch at the desired rpm. But I’m sure others who have dug deeper into our cars here might have an alternative method

 

What's the goal? You could build a completely independent system to "do stuff" based on RPM using an Arduino, or other similar device.

 

OP some info on your goal would be the only way someone knowledgeable could help - I’m hoping you’re trying to build an exhaust flame thrower to build up rich fuel and blast at every shift🤣jk

 

Yeah, everybody's got good points. I had started looking at the Arduino thing and got scared away due to my lack of technical training past early OBDII. I had used something similar to control the speed/volume of a electric BMW water pump in a Water to Air intercooler system but don't think I can handle building one from scratch.
It's for the exhaust valves in the custom setup I've installed. I am currently using an adjustable vacuum trigger switch which works fine under load and boost. I'm thinking there are times when the tach is passing 3500 rpm's and it's not under load or boost so the valves are closing...... really at that point an rpm trigger should just keep them open? Isn't that sort of what's going on with the factory Akrapovic setup ??

 

Ignore OBD. It’s relatively simply to read rpm if that’s the only input. I am not trying to oversimplify. This will be a fun project. But this is also very possible with an arduino and zero integration with the on board ecu or OBD.

 

Ok, so then consensus says I need to have another look and educate myself on Arduino, and find out where to pull the Tach signal from.........

 

This.... they use an RPM 'window' switch for Nitrous applications (on/off for a programmable rpm window) even though I just need a simple 'ON', sort of like a simple shift light.

Widget Man RSA -- Self-Learning RPM Window Switch UPC 767571999224

THIS AIN'T GRANDPA'S RPM SWITCH -- AND IT AIN'T JUST FOR NITROUS!Put simply, the RSA is the best RPM window switch EVER. Get full window functionality with 4 button-pushes and zero engine configuration. Or get simple on-off function with two pushes. The RSA uses a patented technique to adapt...

gkgoodcheapparts.com

According to this it's possible to tap the negative side of one of the coils, but I'm not sure if that's the best way ?? It's a 'high' voltage signal. Maybe better to source a 'low' voltage signal from the ECU, or cam/crank sensor ??

Currently using a vacuum switch to activate at near zero vacuum and boost but there may be situations when the valves might close if there's engine vacuum over 3500 rpm's and should be staying open. An RPM trigger would ensure they stay open and I think that is the only feature I'm missing that the factory setup has.

 

Pick up an MCP2515 Can Bus Shield to have full access to the data stream. Connect it to an Arduino. You can then program digital outputs (high or low / 0 or 5v). You can make it as crazy and complicated as you want. Use a relay to supply 12v power to whatever device you want to control.

 

Pick up an MCP2515 Can Bus Shield to have full access to the data stream. Connect it to an Arduino. You can then program digital outputs (high or low / 0 or 5v). You can make it as crazy and complicated as you want. Use a relay to supply 12v power to whatever device you want to control.

Yikes..... maybe one day (or week) I can sit down and take time to injest all that. Way over my head.

What's the goal? You could build a completely independent system to "do stuff" based on RPM using an Arduino, or other similar device.

Seems like such a simple goal, only one thing needs to be accomplished.
When RPM's go past say, 3500..... all that needs to happen is a solenoid is grounded. This blocks the vacuum feed to the exhaust valves and they pop open allowing free-flow

 

Think of it like triggering a Nitrous solenoid, only there's no upper limit setting.

 

You will need some type of programmable controller that has logic to say "if this happens, do this". Unfortunately there is no simple solution for such a simple task. I get it. So the goal is to just open the valves at a specific rpm? You could do something based on just load by using a vacuum actuated valve. Unfortunately, you will only be able to keep the valve open under load, and it will close under vacuum (or vice versa, depending on the type of valve, normally open vs normally closed).

CAN bus is the least intrusive way to go. I haven't seen the pinout for the 4c, but there may not even be an rpm signal. Everything nowadays is canbus. There are tons of guys that can write code for the open source CAN setup mentioned above. Do a search on Fiverr. There's tons of guys there that can write the code for a small fee. P.S. I have a lot of experience designing and constructing full mil spec harnesses for race cars from the ground up. If you had an aftermarket ecu, this would be much easier. I would not recommend this unless you are going full on race car haha.

 

You will need some type of programmable controller that has logic to say "if this happens, do this". Unfortunately there is no simple solution for such a simple task. I get it. So the goal is to just open the valves at a specific rpm? You could do something based on just load by using a vacuum actuated valve. Unfortunately, you will only be able to keep the valve open under load, and it will close under vacuum (or vice versa, depending on the type of valve, normally open vs normally closed).

Right, so far I have that using a torque converter lockup switch (universal) that can adjust from 10psi vacuum to 0, have it about set about 2 psi. Now I understand the reason to have an rpm threshold since the valves will close again if you go any distance while 3500+ without your foot on the gas. I'd expect that is not an ideal situation.
the 'old' post....

https://www.4c-forums.com/threads/tubi-ish-non-ecu-controlled-active-valved-center-exit-exhaust-experiment-w-akrapovic-cf-tailpipe-finisher.71398/?post_id=1196793#post-1196793

CAN bus is the least intrusive way to go. I haven't seen the pinout for the 4c, but there may not even be an rpm signal. Everything nowadays is canbus. There are tons of guys that can write code for the open source CAN setup mentioned above. Do a search on Fiverr. There's tons of guys there that can write the code for a small fee. P.S. I have a lot of experience designing and constructing full mil spec harnesses for race cars from the ground up. If you had an aftermarket ecu, this would be much easier. I would not recommend this unless you are going full on race car haha.

canbus
I'm not even sure if I want an ECU tune yet. I guess the best route to go in my situation is to buy that programmable switch and 'train' it off the negative pulse from one of the coil packs.

 

I do not have experience with this specific controller, but it looks like it should do the trick for you.

Diagonal Systems - CAN Bus Input / Output Controller

CAN Bus Input / Output Controller

www.diagonalsystems.co.uk

Diagonal Systems - e-shop

www.diagonalsystems.co.uk

 

Here's another one... pretty much exactly what you need!

Lingenfelter CANR-002 CAN Based Relay Controller Module

Check out the deal on Lingenfelter CANR-002 CAN Based Relay Controller Module at Lingenfelter Performance Engineering

www.lingenfelter.com

 

And one more option. Can place these in a small abs project box. But, you will need to do some coding.

Adafruit RP2040 CAN Bus Feather with MCP2515 CAN Controller - STEMMA QT

If you'd like quickly get started with CAN bus interfacing, with no soldering required, our Adafruit RP2040 CAN Bus Feather comes ready-to-rock with a microcontroller, CAN chipset, and terminal blocks for instant gratification. The controller used is the MCP25625 (aka an MCP2515 with built-in...

thepihut.com

Combined with...

Adafruit Power Relay FeatherWing

A Feather board without ambition is a Feather board without FeatherWings! This is the Power Relay FeatherWing. It gives you power to control, and control over power. Put simply, you can now turn on and off lamps, fans, solenoids, and other small appliances that run on up to 250VAC or DC power...

thepihut.com

 

Why don’t you use a shift light or shift beeper if all you need is a trigger? You can run a relay switch to it. Simple and fool proof.

 

And one more option. Can place these in a small abs project box. But, you will need to do some coding.

Adafruit RP2040 CAN Bus Feather with MCP2515 CAN Controller - STEMMA QT

If you'd like quickly get started with CAN bus interfacing, with no soldering required, our Adafruit RP2040 CAN Bus Feather comes ready-to-rock with a microcontroller, CAN chipset, and terminal blocks for instant gratification. The controller used is the MCP25625 (aka an MCP2515 with built-in...

thepihut.com

Combined with...

Adafruit Power Relay FeatherWing

A Feather board without ambition is a Feather board without FeatherWings! This is the Power Relay FeatherWing. It gives you power to control, and control over power. Put simply, you can now turn on and off lamps, fans, solenoids, and other small appliances that run on up to 250VAC or DC power...

thepihut.com

On the right track, just was hoping there was something more automotive specific related. MSD ignition has it, MSD... 8950, 8670, & 8913. Rpm switch, Module, and Tach driver respectively. Over $400 because of course, they couldn't put it into one simple unit

Why don’t you use a shift light or shift beeper if all you need is a trigger? You can run a relay switch to it. Simple and fool proof.

Exactly, but it's the elusive tach signal that is the necessary evil for even a shift light. Seems to point to the 3 MSD components listed above to achieve that. The more I examine it, the more that 'Widget Man' RSAv10 makes sense. You don't Need an RPM selector because you set it while the vehicle is running at the RPM you want to select... ? $60 for a single component, or $400+ for 3 different boxes to achieve the same result (although the MSD is a name brand and more analog in set up)