Thinking of a more subtle 3.5" exhaust

[SCapelo]

My gt40r full stainless 3.5" vibrant exhaust has done me well and sounds great.. but it's stupid droney and obnoxious.

I'm thinking of a 3.5" in 2.5" dual out rear muffler with a vacuum valve cutout on one tip to restrict it and quiet down when I want - copying some of chikinhed's setup some years back. I'm hoping this doesnt restrict it much when wot to the point I can feel.

The thing is - I dont really want an electronic cut-out. I used to have one on a neon srt-4 some years back and the open dump was horrid. Response time felt like forever too. Probably used it once.

The idea here is to use a vacuum actuated, normally open, exhaust valve that I can toggle on and off via a switch to a purge valve of sorts. That way I can decide whether it's open or closed on first start up with press of a button. The thing I'm not sure of is when boost enters the equation. Of course I'd need the valve open for max power, but I don't want to have to hit a button every time I want to go Wot. Then on the other hand I dont want to have a quiet car 100% of the time I'm out of boost, ya know?

Anyone else done something like this? Or is it full race car full time? The other day I found myself complaining about my neighbors leaking flex pipe on his 98 Honda and lately I've been afraid my car draws way too much unnecessary attention lol

[pbonsalb]

I have a 3.5 with a center straight through Magnaflow muffler and a rear straight through Magnaflow and it does not drone and is not stupid loud.

[SCapelo]

My current center is just a straight through vibrant 3.5 resonator which probably contributes to most of the noise. But I wonder if changing that alone will be enough. Whereas the rear muffler + valve idea I could at least decide what kinda noise It makes depending on the situation.

Almost every later bmw exhaust has had some sort of valve on it to get the best of both worlds. Being stock ecu kind of limits my control over said valve though. I also paid dearly to have this exhaust done the first time around so I'm hoping I can do it just right and make it a win-win

[Kevin325i]

Here's what I did.








I used this valve.

https://www.aliexpress.com/item/Tans...6c9d4e50zoGQRo


To be perfectly honest I wanted it to open immediately because I'm putting a solenoid in it to hold the valve closed longer but I wanted to be able to have a default open configuration. With the camshafts in the car it doesn't pull much vacuum so there's a check valve- vacuum canister configuration as well. Without the solenoid the valve opens a little bit too quickly and easily. Cruising on the highway it can fully open very easily and it's a little annoying, it's pretty much the entire reason for the solenoid.

Borla 40004s mini muff in the back, 40946 in the middle, 3.5" turbo back, dual 3" tips with a 1.75" bypass around the flappy valve.


https://www.youtube.com/watch?v=Ko_SZhIj04g

[pbonsalb]

A couple of larger mufflers might be enough. My rear is 3.5 out but from there adapted into twin 2.5 or 3.0. Works for me. Resonators arent great mufflers. But if you want to do a vacuum boost operated exhaust, it should work. Like you wrote, Chikinhed made one and likes it and BMW has used them for decades.

[SCapelo]

That is exactly what I was looking for!
It's hard to tell in the video, is there a big difference in sound with valve closed? I've been looking into how the corvettes do it on the c6. They have some sort of controller that most people trick into staying open all the time (stock exhaust problems). I'm wondering if that could be adapted but I think it's all tied into the ecu too for rpm / speed reference.
I like chikinhed's approach with the 3.5" in dual 2.5" out because it traps half of those gasses in the muffler itself. So I'm wondering how effective yours is with the single in/out muffler. It would be pretty easy to adapt that to mine to try it out.

I may need to suck it up and get a boost actuated one and be happy.

[SCapelo]

I think I may start with this as a rear muffler here:

https://www.jegs.com/i/Magnaflow/642...BoC9TwQAvD_BwE

And pull the two outlets closer together to fit out of the factory location. Boost actuated valve on one of the outlets and try it out. That way even if its closed at low rpm, at least it's still got a 3inch outlet so it doesnt hurt spool. And the fact that it traps some of the gasses inside the muffler itself might quiet it down enough to cancel most if not all of the drone.

[Kevin325i]

It's a pretty decent change. I have no regrets.

The exhaust still has to bounce off the valve and is forced to interact with the packing in the small muffler for longer. The major issue doing it how I did is that 10% valve movement is basically 100% noise. When the valve is sealed up you're good though.

[lisnowboarder]

i had plans to do this aswell. But after getting a magnaflow muffler and hacking it to fit i dont think ill have the room. To your question about boost open vs vac i would assume you could pull the valve appart and rotate it 90 degrees for normal closed condition tell boost. My plan was to tee off my electronic boost controller power feed so when its stage 1 (wastegate) purge valve is closed and valve stays closed. When stage 2-3 activate to allow air to pass. But I tend to make things complicated.

[pbonsalb]

Starting out with 28” overall, 22” body will make fitting harder. Consider 18” overall and 14” body.

[Def]

I was thinking about a boost operated exhaust valve in my MR2 too. You can get one that's a bit later to open by getting one that's normally closed but then pushed opened by boost, rather than normally opened and pulled closed by vacuum. They're not as common, but they are out there, so you can probably get 4-7 psi of boost before it cracks. This would primarily make it easier to build a passive system without a solenoid to keep the sound down while cruising etc.

[Kevin325i]

https://m.aliexpress.com/item/327070...A1548713650170

But then no option for "always loud"

And my bypass is intentionally small cause it seems to help low speed combustion stability without having to decrease lambda target at cruise.

[chikinhed]

I used a VW 1.8T IWG actuator for the valve on my muffler. It open at 7 psi and causes no increase in back pressure as measured just after the turbo. I’ll try to post pics up soon.

[Def]

Do any of you guys use the valve in the way of your primary exhaust path? Or do you always have a bypass? In the MR2 it'd either be in the 3" primary exhaust path just after the cat, or on one of the ~2.5" outlets of the muffler. Not sure how much sound reduction I'd get blocking off one 2.5" muffler outlet, given the other 2.5" outlet is open via a straight through muffler as well.

Versus I could put the valve in the 3" tube upstream of the muffler and have a small area (like 1.5" tube equivalent) always open, then open it fully under boost.

[Kevin325i]

I was concerned that putting the valve in the primary flow path without a bypass would cause the valve to be forced open and rattle at idle.


If I were making it for an Mr. 2 I would just put the valve before a more restrictive muffler than what you have since you wouldn't be dumping exhaust under the car. You can face it straight out the back.

[Def]

There's really not much space back there, so it's really tough to do more than 1 muffler. I did get a cheap 350Z catback I was going to chop and make work, otherwise with 2 muffler they're really limited in size.

I wouldn't think the valve would rattle at idle if you chop some of it off so it really only sees load against a stop during pulses, but maybe I'm wrong on that. I'll have to play around with some blocking ideas to see what makes the most difference in sound.

[Kevin325i]

What I've seen with mine is that the valve needs to be completely sealed to get any real benefit. As soon as it opens slightly it gets much louder. More muffler volume would probably help in that aspect.

[Def]

Interesting... that would make some of my options not work at all. Space is really tight for mufflers tho' - the midengine struggles...

[Kevin325i]

You could almost put a normal factory muffler and have the valve at the inlet. Then put a tip on bypass out the back and a matching out of the muffler

[SCapelo]

Its the same deal for the e36, not a heap load of space. So the blocking of one outlet will have to do. But of course there aren't many single 3.5" in and dual 3" out or even 2.75 / 2.5 outlet options that dont have a long body. I may have to cut one open and shorten it for it to make sense.

[chikinhed]

My valve does not rattle at idle. I chose to put the valve at the outlet on purpose to take advantage of the volume of the muffler as a helmholtz chamber for the leg that is blocked off. Both paths through the muffler are equal shape and volume on mine. I have a Borla XR1 as a center muffler and the modified Magnaflow at the back. When cruising I hear engine and tire noise. You can have a conversation with low volume music in the back ground. There is zero drone. It’s what I was shooting for, a fast quiet car. When it is at WOT the valve opens at 7 psi of boost and it gets louder. The sound it makes is a higher pitch but lower volume than the straight through 3.5” Dynomax I have but the Magnaflow puts me over the dB limit at the track at 95 dB due to the frequency weighting their dB meter is set to. In the car at WOT, the Magnaflow is much quieter with no drone compared to the Dynomax which has drone and is loud but the Dynomax has a deeper tone outside that passes the track dB meter at about 85 dB. Both mufflers are mounted with v-bands so I can swap for track use.

[chikinhed]

Over the years I have tried many mufflers and resonators. The thing that I’ve learnt is that there are so many false claims from the manufatures and BS reviews that you need to analys the design yourself and do proper back pressure and sound measurements on your own car to determine if the exhaust system is going to be a massive restriction and/or be loud. My first taste of this was with the AA track pipe which did very little for reducing back pressure but did make it louder. It was shiney though

[pbonsalb]

You should be able to roll a tennis ball through the exhaust.

[philly98540]

I tried many different mufflers over the years from various brands. The claims and reviews need to be taken with a grain of salt for sure. Lots of BS out there. I'm SC'ed with headers, so a bit noisier than a Turbo car. What I found was you need to get the largest body muffler you can fit. The larger 22"+ long body straight through Magnaflows are a lot quieter than the 18" and smaller length bodies. It makes a big difference in sound attenuation. After fitting the jumbo body muffler, the sound was way down, but I had some drone at 1700 rpm. I added a J tube of the proper length to cancel that out. I used a phone sound app to the get frequency to calc the J tube. Very happy with the sound now. I can goose it when I want without drawing too much attention and can cruise in a quiet cabin.

Doing the cut-out is a cool idea, but on a street car, it limits how and when you can get on it. If you can make it quiet enough all the time, that is better IMO for a street car. Less chance to get pulled over. If the cut out opens everytime you get in boost, then you'll end up driving it soft more of the time and that kills the fun.

[chikinhed]

Even when the valve opens, the exhaust is going through the muffler and it’s not that loud.

https://m.youtube.com/watch?v=ZjDQDRAbd_w