Rear exit exhaust

[neilkuy]

New to the forum and hoping to put in an order soon.
I know this topic has been touched on in the past, and has been done successfully on the gen2 coupes.
Reference
https://www.ffcars.com/threads/build...pe-674.622602/

In my planned build i would like to run the exhaust on the underside of the car to the rear of the coupe in an effort to reduce sound. The goal is to make this a *daily driver. I am curious to see the underside frame of a Gen3 coupe to understand the differences. The challenge as I understand is that to pass inspection the exhaust can't be lower than the frame of the vehicle.

I would love to see pictures of the underside of a solid axle coupe and an IRS coupe. People have said it "just can't be done". Honestly this sounds more like a challenge. I imagine many of us taking on projects like these can understand that feeling.
I am hoping to start a build soon and trying to work out some of these details.
Please share pics of the underside of your gen3 coupe frame, especially the mid and rear section perhaps from the rear.

Thanks in advance.

[racingandfishing]

Check out EdwardB's thread.

https://thefactoryfiveforum.com/show...l=1#post310781

One thought may be to use the side pipes to run the exhaust at least that far back and then tap into the far end of the backs of the pipes to finish running it to the back. You could cap the sides or baffle them on the inside. My car is still on order, so not sure if you can get any further back though or not as it is pretty tight according the pics I've seen.

Anyway, I will be following as I would really like to have an exhaust selector/captains call to quite the side pipes and run it out the rear when cruising or around the neighborhood.

[neilkuy]

That thread has some good pictures for reference. Post 635 also shows a top view with the transmission in place. Seems like there is some space beside it - heat would be an issue. But even more the rear diff really has no way around it. Seems you may even be stuck using the approach you share because getting past the rear end seems limiting.
Curious to see the same images with a solid axle.

[Blueblood]

My first build was a 1930 model A coupe that I initially ran the exhaust all the way out the back. The drone was unbearable so I shortened it to in front of the rear wheels, still very bad drone the final Stage was lakes style header exhaust that I built fiberglass baffles into. That was by far the best variation of all the exhausts I had in the car. That being said I guess my point is that running it out to the rear end to quiet it down my actual make it worse. I am very close to finishing my gen 3 and there is very little extra room to get pipes run all the way to the rear. I’m not saying it can’t be done just what are you willing to sacrifice to achieve that goal. It may work great and the best of luck.

[racingandfishing]

Thanks for that and drone is a real issue I didn't think about. Though in my 2015 Mustang, it was dependent on the aftermarket exhaust you used. I used a Ford Performance/Borla and had no drone, but lots of other owners reported drone with other aftermarket exhaust. Being I don't have the testing facilities or dollars of Ford/Borla to come up with a system that doesn't drone, I will likely be using the Gas N Pipes.

[Logan]

I would suspect the best path is as mentioned above.... Run the exhaust in the standard sidepipe location (below door sills) then turn it inwards just ahead of the rear tire and work around the rear suspension to a rear exit.

A few points:
1. There will probably be no room out back for mufflers, so putting mufflers in the stock sidepipe location is probably the best (only) option. The upside is you could fill the entire sidepipe location with baffling, easy to get 50% more than the stock FFR pipes there.

2. You could build "covers" for the mufflers, make it look like the body continues all the way down, totally hiding the fact that there is any exhaust located below the doors.

3. Longer total pipe length, and the many benefits that brings

4. This is how the F9 is built with it's rear exit exhaust. The F9 is a modified Gen3 Coupe frame, so with enough cutting and welding it is definitely possible.

5. I'm genuinely curious how exhaust tips would look on the rear of this car. It was never designed for them, and it's a beautiful piece of automotive art with the Kamm tail.... How do you envision the tip(s) looking? One central outlet? Through the body, or below it?

[Jeff Kleiner]

Superformance has an option for rear exhaust on their Coupes and they run through the (now dummy) sidepipes to get from the front to the rear. I don’t know if there is baffling in those pipes but suspect there is.

Jeff

[GT77]

As one attempting to fabricate rear exit exhaust on a Gen3 a few comments from my experience so far. I choose to attempt piping the the exhaust the down the transmission tunnel opposed to the standard side pipe location due to complications of trying to tuck the piping back under the car in front of the rear tires. Biggest things to watch out for are the control arms/rear frame triangulation being in the same spot as where the piping needs to turn a 90 towards the back. There may be space to stuff the pipe right behind the rear seat (properly firewalled and sealed off from the passenger compartment), but it has been a long time since I looked at this option. It is likely possible, but I chose not to go this route so I can't speak to details of the above suggestions.

Observations attempting to pipe down the transmission tunnel
- The transmission tunnel is very tight. With the engine offset towards the passenger (RH) side, the right side piping down the down the tunnel is an exercise in how many bends you can make in a piece of exhaust tubing.
- Most shorty headers don't work. I am extensively modifying a stock set. I can't say that I looked at all the options (and running a non-standard engine which further limited my particular options), but I wouldn't expect to find something off the shelf that works perfectly in the tight engine bay.
- Heat - the headers are right next to your feet and the entire first 4 ft of the exhaust (the hottest point) is right along side the seats. I am fabricating additional aluminium panels and insulation to try to offset this, but the this is a real concern.
- Getting the pipes past the transmission mount is the tightest point in the tunnel. I changed the transmission mount to make the piping easier.
- I am using 2.5" piping and IRS - solid rear axle would be difficult with the suspension articulation and the driveline.
- If wanting the piping to exit out of the rear body work, the stock fuel tank doesn't work as it extends to basically the rear fiberglass
- Limited options for muffling which as mentioned earlier may make the entire exercise and extensive fabrication moot.
- Consider the unknown downstream effects of the modifications (i.e. all the other pieces that have to be moved/modified/removed in order to make achieve the goal. These add considerable time to the build.

Overall, it is possible, but it comes down to compromises and time. I am not trying to be negative here, but rather setting expectations correctly. If you have the skills and time to fabricate, great! - that is what I love about these cars is that they are relatively "easy" (compared to rusted out classic production cars) to modify and paint outside the lines of a normal build. If not, a set of foam ear plugs are a cheap, time saving, and easy "modification" compared to trying to find off the shelf (or even custom fabricated) components that work together to achieve this end. I am probably > 60+ hours in modifications into just making the rear exhaust work and I am only 30% done. Best of luck on your decision.

[Rsnake]

Options do exist for a quieter side pipe. I have one that will pass the 90db limit at Laguna Seca.
Really quiet on the street.

[racingandfishing]

I want the best of both worlds...!!! I really like the look of the dual pipes but want something more subdued...so like I said, seems like Gas N Pipes will be the direction I go. Though in Bob's Daytona build thread he cut the ends off the factory pipes and inserted these https://www.carchemistry.com/3-disk-insert-3-diameter/ and than is putting the ends back on again. Interested to hear them once he gets a video.

[neilkuy]

Options do exist for a quieter side pipe. I have one that will pass the 90db limit at Laguna Seca.
Really quiet on the street.

Rsnake, what exhaust do you run?

[neilkuy]

Thanks GT77, this is great info. Have you seen the frame with a solid axle. I agree you have to worry more about moving parts. I am eager to put an order in but the solid axle vs irs is my one of my bigger gating items.

[neilkuy]

I want the best of both worlds...!!! I really like the look of the dual pipes but want something more subdued...so like I said, seems like Gas N Pipes will be the direction I go. Though in Bob's Daytona build thread he cut the ends off the factory pipes and inserted these https://www.carchemistry.com/3-disk-insert-3-diameter/ and than is putting the ends back on again. Interested to hear them once he gets a video.

Good idea with the inserts. This would seem to resemble a motorcycle exhaust. So it should be doable without killing too much power. It would be disappointing to lose too much of the sound outside of the car but if you can't get it to the back, it is a decent option.

[neilkuy]

I will include this here for reference on how to include a muffler up front.
Here is an example of an LS1 based Coupe with mufflers. He used short tube headers and sent the exhaust forward so he could include a muffler before it came out the side. His doesn't include the side pipes but you could easily include them in this approach. I am curious though if it is quieter at the driver with the tips forward like this. Also eliminates the heat at the underside of the doors.

https://ls1tech.com/forums/conversio...onversion.html

[racingandfishing]

Good idea with the inserts. This would seem to resemble a motorcycle exhaust. So it should be doable without killing too much power. It would be disappointing to lose too much of the sound outside of the car but if you can't get it to the back, it is a decent option.

Can't take the credit. Here is the post.

https://thefactoryfiveforum.com/show...l=1#post498507

[GT77]

neilkuy

Sorry, I don't have good reference with the solid axle as I am not using one/considered my design to allow for it. Right now, the driveshaft and the two pipes form a "triangle" when looking down the transmission tunnel. There isn't much clearance. I don't see how you could get a solid axle through the space with any vertical driveshaft/suspension movement without hitting the pipes. Maybe if the exhaust pipes were all the way into the corners, it maybe sufficient, but again it would hard to conclusively say without mocking it up. Once clear of the rear tunnel lower cross member (right below the differential pinion flange) I would imagine there would be space to drop the pipes below the solid axle, but I cant say whether this would impact the ground clearance.