It took me a while to figure out what exactly I wanted to do with the exhaust. I ultimately decided to run dual 2.5" tubing off of the manifolds and join them behind the transmission to single 3" tubing. I decided on this route mainly due to the simplicity of routing and cost. The entire system is built from mandrel bent 16 Ga 304SS tubing and a XR-1 Oval Borla muffler in the rear. The initial installation sounded great at WOT but was extremely loud at cruise and had substantial drone, a second round muffler reworked into a 'D' shape was installed in the transmission tunnel which helped substantially. The system is still quite loud but is tolerable for cruising and longer trips.
This was my first stainless steel project and there was a bit of a learning curve with the welding, but overall it out nice. If I was going to do it over again I would have picked up some Solar Flux for the inside of the welds, this would have made everything look much nicer. I picked up a few additional tools to complete this project....the main one being a Milwaukee Dry-Cut chop saw. If you plan on doing a lot of tubing this is a great tool to have. It cut the tubing easily without much of a mess and makes nice even cuts for welding. For this project I purchased all the tubing from Global Technology and Engineering, Ive found they have pretty good prices and you can buy the bends in 15 degree increments up to 90.
The 350z manifold outlets point straight out the rear, pointing directly at the firewall of the 240z. Since I eventually plan to go turbo and will fabricate headers at that point I wanted to save money where I could I decided to modify the factory manifolds for the initial N/A installation. I cut the ends of the OEM manifolds and welded tubing directly to them, turning the exhaust down the firewall ad into the transmission tunnel. I had some concern about durability of the weld, but it has held up very well without any cracking issues. I welded the joint with standard mild steel welding wire in my MIG.
To mount the exhaust to the manifolds I opted to use the factory flanges. I drew up mating flanges and had them CNC cut at work from 1/2" 304SS. It took a while to whittle them out but they turned out beautiful. Looking back I probably would have used V-Bands, but at the time the extra expense was not worth it to me. I've also had issues removing V-bands after they get fused in place over time.
I was able to get the exhaust pretty tucked up under the car, it is even with my frame rails. The transmission crossmember also worked out well allowing for plenty of space to keep the exhaust tucked up. You can see the location of the flanges here as well, they will be easy to hook up to any exhaust header/turbo layout in the future
Welding and more welding...It took several hours to finish welding the exhaust. I added a flex pipe as well as 4 oxygen sensor bungs in the down pipes to finish it up.
I used Summit Racing exhaust mounts to hang the rear of the exhaust, one at the muffler and one at the differential cross member. They are basically just strip of stainless with a nice snap together polyurethane bushing.... and are WAY over priced.
After getting the car on the road the first thing I realized was that my exhaust was way too loud for the street, however the worst part wasn't the noise but the drone. There was so much drone that for a trip of any distance I had to put in ear plugs. When I built the exhaust I knew I might have issues with drone but i was hoping for the best.....
I talked with Borla tech support about the issue and they were very helpful. They told me the oval XR-1 was pretty much the same as their XS and turbo street muffler since it had a lot of packing. After looking at pictures of my car and the space limitation they recommended another XR-1 (round, 15" length) as a resonator as close to the engine as possible.
I the only place the muffler would fit was right behind the Y pipe in the transmission tunnel. Even at that location it required removing my flex joint and hacking up the muffler. I always wanted to know what these things looked like inside anyway....
To gain much needed ground clearance I started by chopping the bottom of the muffler off and welding the section back on flat, this was a little tough to get straight but it turned out decent:
Finished product..you can see the horizontal section as well, this was a bit harder as the muffler didnt want to stay round after I cut it. I ended up taking about 1.5 inches out of the length. Still learning on the SS but it turned out pretty good.
Overall I very happy with the outcome, the car is MUCH quieter in partial throttle conditions and cruising around. Its still pretty angry sounding at WOT but you can hear the 'stock' VQ note hiding in here. Check out to videos page to hear how it sounds.