A Quiet Exhaust

My issue with the loud exhaust isn't my own hearing, it is the police that get a bug in their ass. I have had to "evade" them twice cause they were trying to run me down. When I am laying into it, you can hear me over a half mile away. I have also been harassed by a few people, simply because I drive past their house frequently. I don't like the chambered muffler because is gets dramatically louder when there is any load on the engine. You can't do anything to stop it from getting overly loud if there is any kind of grade to the roadway.

I recognized all this, and realized I would also like to hear my supercharger sounds over my exhaust anyway.

I started to do some welding. I have never welded before, so I have been making mistakes along the way, but I am also learning how to fix them. I can't weld any more of the assembly, until I have the sling up on jackstands and remove the 1320 exhaust.

Then I can bolt up the flex coupler/catalytic convertor section, and hang the muffler/resonator section, and figure out the elbow to connect the two assemblies. I was hoping to have the exhaust exit out the side, but I won't be able to mock that up until the complete assembly is in place. I also need to 3D print some pie cut templates.

It may not look pretty, but it's not gonna come apart. I am going to be wrapping the exhaust, starting at the exit of the cat, to the exhaust tip, just like my I did with my 1320 exhaust.

When removing my 1320 exhaust, I noticed it was blowing apart. I am going to clean it up and weld it back together.

Got a little further with my welding;

Mock up in the vehicle;

My goal now is to make it a side exhaust. It is going to be tight, but I can see it is possible. I ran out of gas for my welder, so I am moving on to other projects for now. I don't know how loud/quiet it is going to be, but I can't wait to hear it. I am just hoping it is not as loud as the 1320 exhaust when cruising. For what it is worth, I have had this same Borla muffler on another car, and I liked it, which is why I chose it for this project.

I decided to try it in the factory exit position, because I don't want to do the extra work to make it side exit until I know if I like the sound/volume or not. I put on the flared tip from my 1320 exhaust.

I started it today, in the garage, and I wouldn't say it is quiet. The tone is somewhat what I expected, but a little louder than I was hoping for. It is a complete exhaust, with a cat, resonator, and muffler, but the overall length is really short. The cat is capable of flowing enough airflow for 500 hp, and the resonator and muffler are both straight thru design, so it is free flowing for sure. I know for sure it is going to be loud when I am laying into it, but I need to drive it around to see how loud it is when cruising.

Wrapped;

Installed;

I installed one of those perforated cone exhaust inserts. I went for a ride today to bed my new Wilwood brakes, and to see how my exhaust sounds.

Prior to my drive today, I was totally prepared to take off my exhaust and put the 1320 back on, because of how loud it was the first time I started it. With the perforated insert, it is definitely quieter than the 1320 exhaust, and I didn't notice any drone when cruising. I spent most of my drive trying to see how quiet I could be, and trying to make it drone. When I did lay into the throttle, it sounded awesome. I don't know if I am going to bother with making it a side exit, based on how it sounds now.

Between buying a welder and supplies, building a welding station, and buying all the parts to fabricate my exhaust, I spent over $3000 on this project. After driving around today, I have no regrets. I got the exhaust that I wanted, and I learned a new skill.

My next exhaust project is going to use the stock muffler, a cat delete pipe, and a vacuum or boost activated cutout. I am going to 'Y" off of the cat delete pipe. There are three different styles of vacuum/boost cutouts. I still have to narrow down exactly which route I am going to go. Keep in mind I have a supercharger, and I do not want to compromise anything in regard to the tuning, or risk any kind of engine or supercharger damage. I just want the exhaust to be open when I deliberately lay into the throttle.

One style opens at 6-7 pounds of boost, which is too high to be safe or practical. One style needs 14-16 inches of vacuum to stay closed. I am always watching my vacuum/boost gauge to make sure I am not bogging down the engine too much (don't want to run near zero vacuum at minimum throttle position, so as to not damage the supercharger), and to be practical, 6-8 inches of vacuum would probably be tolerable given how I drive. If I drove really conservatively, I could stay at greater than 6 inches of vacuum for most driving situations. These two styles require no electrical components, as they are hooked up to manifold vacuum.

The third style, I need to look into a little further. It uses vacuum, but requires a vacuum solenoid (valve) and a switch to operate the vacuum solenoid. I have no interest in hooking up a toggle switch, because I want this cutout to be self actuated and stealthy. I have found a low pressure switch, meant for supercharged applications, that activates at one (1) PSI of boost. This seems to be the most practical to me.

Quote from FunCycle

You can also bypass the cat in the stock muffler to give yourself a nice sound and a little more performance. Easy to do. This is what is what is running on Sling II. I have never got around to putting the Welter Duals on.

Driliing a hole in one chamber of the stock muffler, which you have described in previous threads, is the opposite my goal (see, I read your post's in detail). I want the stock muffler to be as quiet as possible, so it needs to stay whole.

The cutout that I want to install is before the muffler, in the cat delete pipe, so the muffler is not going to contribute to the sound when the cutout is open. I would prefer electric car silence, until my supercharger is making boost. When the supercharger is making boost, I want an open header. I can get close to this goal with the cutout.

I have four exhaust systems for my Slingshot. I have the stock setup, a ZZP setup with header and muffler (they don't make them any more), a 1320 header and muffler setup, and my custom setup that I welded myself. I have not found what I like yet, and it is not out there in the market either. I have listened to sound clips of every exhaust currently made, and those no longer made for the Slingshot.

Every manufacturer is making their exhaust to their signature sound, and none of them have a goal of making it quieter. I like the sounds of a lot of the exhausts, but again, I have my own goals.