bjmsam

With the fuse pulled, my stock exhaust sounds fantastic above 2000 RPM but exhibits excessive drone below 2000 RPM. I would like to replace the fuse and lower the activation RPM from 3500 RPM to something closer to 2000 RPM.

I am aware of products that enable adjustment of the bimode exhaust activation RPM by monitoring engine speed via the OBD2 port and switching the vacuum circuit, but as these often interfere with ELM devices used for datalogging, I am looking for guidance on using an RPM activated window switch such as this one from Summit or this one from JEGS. Will these devices properly interpret the signal on the Engine Speed wire connected to the ECM? Does the vacuum circuit draw more than 3 amps and therefore require use of a relay? Has anyone already done this and written it up in a post that my searches failed to reveal? Thanks!

Unreal

Dash logic can control it.

bjmsam

Sorry if I was unclear.

DashLogic is among the devices to which I referred above.

So is the Exhaust Commander Elite (presumably - there has been no reply).

I am looking for answers to the following questions about RPM activated window switches:

bjmsam

This approach controls activation based on engine speed and load - neat!

erikszr1

that'll do it

bjmsam

I'm hoping to get away with this:



This assumes that the exhaust circuit is disabled when the ignition is off (I've seen posts suggesting that it is always energized which makes no sense to me) and that the RPM switch can interpret the 5V tach signal (may need a pull-up resistor).

mike100

^^ the vacuum solenoid I used allows vacuum thru them when no power is applied. This will close the muffler flaps. Applying 12v will cause the solenoid to block the vacuum source and vent the downstream end to the atmosphere allowing the vacuum diaphragms to open up and get louder.

I found that late 80's to early 90's style GM EGR solenoids to work in this manner. They have a calibrated brass restriction plug (you have to drill it out), but you can get these at junkyards everywhere. They are on 350 v8 rear wheel drive cars and those 4.5 or 4.9 cadillacs front drivers that litter the wrecking yards. Even if money isn't the point (the solenoid is $60 new), going to get used parts is still something to think about because you can grab a bunch of that high-temp plastic vacuum tubing and a bunch of the factory rubber elbows and 'T''s that fit nicely on all of the connection points.

Hib Halverson

I suspect the reason the OP wants to change the enable RPM of the dual-mode exhaust is that it's too quiet when the valves are closed but had too much "drone" at low rpm with the valves open.

My solution to this problem worked quite well, cost only a buck or so and a hour or so of work and left the system with full computer control.

See this thread elsewhere on the CF

bjmsam

I've already done similar (description here) but now want to control the RPM at which the flaps fully open.

Very interesting! Would venting to the atmosphere cause a CEL?

BearZ06

Why not just a foot switch in the dead pedal to control it to your desire? Too simple?

bjmsam

My switch is conveniently located in front of my center compartment, but I find myself constantly flipping it at around 2k RPM, hence this quest for automation.

mike100

Nope...remember the vacuum source is completely independent of the manifold vacuum and any sensors. completely add-on.
the vacuum source is kept up with a 1-way check valve exactly the same way the brake booster is (but just a smaller version). The typical uses for the on board vacuum are for hvac vent controls, and maybe vacuum actuated valves for emissions. Newer cars are pretty much electric everything, but if you have NPP, you have a vacuum reservoir in the back of the car along with the 3 port vacuum solenoid. Really this is kind of similar to how turbo waste gates are controlled too. All you would need to do is tap into the NPP solenoid circuit with the rpm switch or rather you would disconnect the factory wiring and put in your independent control.

If somebody wanted to be super slick, they could hack the ecm binary and reverse engineer the memory location that holds the rpm value on which the npp is activated.

mike100

A lot of people are happy enough with that scheme...mostly to keep it turned off all the time when driving through town. Some people the opposite

Hib Halverson

The ECM doesn't control the dual-mode exhaust. There is an exhaust controller that does that. A number of people have been trying to hack it or learn how to calibrate it. As yet, I've not heard of anyone who's been able to do it.

bjmsam

I ended up using a #40822 RPM Activated Switch and a simple relay. The engine speed signal for the RPM input can be found behind the knee bolster here. The exhaust circuit is energized when the ignition is off (why?!) so I tapped the seat heater circuit for power. I used double-sided tape to mount the components in the area to the left of the fuse box where the LED can be seen and the buttons can be accessed for adjustment (increments of 100 RPM). Works (and sounds) great!

mjoacim

Off topic, please don't behead me guys. But what head unit is that? It looks wildly factory yet updated at the same time, which I love. I also like having a physical **** for volume control, too. That one appears to have such.

bjmsam

Yeah, you probably should have clicked the link in my signature block (OP).

Android Head Unit & Backup Camera Installation

mjoacim

Awwww, c'mon, man, lol. I wasn't paying attention to that, lol. Thanks for the info, sir!

bjmsam

It's an awesome head unit and actually not too far off topic: I suggested to the seller that future versions should include trigger wires that Android apps could control to do things like... switch a relay when engine RPM exceeds a threshold!

Corvettinator

Epic mod! I was going to suggest this thing based on throttle (as this guy is doing) but yours looks way cooler (and it's way cheaper). With a cool looking readout like that, you should wire in the glove compartment or center console.

I'd love to see a video of this in action.

I have a mild-to-wild button on my shifter, and I usually have the NPP's open all the time. But when closed, I'd prefer to have them open at higher RPM, not lower. Sometimes I want to take off quieter.

Andy of A&A had the M2W on his blown Z06 set up so it was always closed, or always open, but that affects the tune adversely. I drove that car once, very fun.