Nissan 370Z Forum - View Single Post - DIY - Modified NISMO Exhaust

nismolife · 11-26-2011, 12:36 AM

I've seen a lot of threads out there asking if a Nismo exhaust could be modified to at least make it louder and possibly improve it. I couldn't find any real attempts to mod a 09 Nismo can, so I decided to try it. My fall back plan would be to just buy a FI setup, but I wanted to try my hand at it first just to satisfy my curiosity. Note that stock non-Nismo muffler cans may be a bit different, but I'm betting that they are all similar enough to do this mod.

I finished the project and I really like the results. The sound is quiet at idle, but livens up quickly as you get on it. There is *no* drone or nasty rasp whatsoever. I didn't dyno it, but the Nismo is doing some things I'm not used to - like breaking loose on dry pavement at 40mph (2nd gear, throttle only), or 70mph in the wet. Definitely no loss of torque, and the butt-dyno says maybe a small increase was found.

Update: I attempted to record some videos and found out my new phone (HTC HD7) actually has noise cancelling, which does a great job of eliminating the exhaust sound from the video! I'll break out my GoPro cameras & see if I can do better.

The 09 Nismo muffler can has 3 internal chambers. The main exhaust dumps into the center section, mixes, and then exits back out side sections. There are two 2.5" ports in each side section to allow for this flow. There are also a number of other smaller ports dumping into the center section, presumably for tuning the sound(?)

In this mod, I decided I would create a better flowing crossover pipe that joins the two sections, hopefully getting better sound without a loss of torque. The crossover pipe is made of 14 g stainless exhaust tubing from Summit Racing, in 3" and 1.5" sizes Summit Racing SUM-640130 - Summit Racing® Stainless Steel Exhaust Tubing - Overview - SummitRacing.com. I'm a novice welder, so this was my chance to go buy some stainless mig wire & get some practice welding stainless. You need (1) of the 3" and (1) 1.5" piece of the stainless tubing.

First, a tip on removing the axle-back muffler can section - crack all four exhaust flange bolts loose first, before taking them off. I did them right-to-left and by the time I got to the last one, there was enough force pulling against it that the nut stripped and I ended up having to cut the welded bolt off the flange in order to remove it. Shoot some penetrating oil on them as well before attempting to take them off. I couldn't reach these bolts with an impact, so I had to reef on them with my socket wrench, which probably contributed.

After loosening the four main flange bolts, find the bolts holding the mounting brackets to the body - on my car, there were 3 bolts on each side holding triangular steel flanges. Careful with these too, because as they come out, the weight of the muffler section starts to put stress on them - you could end up having trouble with these also - especially take care when replacing them. The idea is to remove the mounting plates - not to try to pull the brackets out of their rubber vibration-isolators. The mounting plates and rubber isolators will just hang off the muffler pieces until you mount it all back up again.

Assuming you aren't still busting your knuckles to get the muffler section out, have a look at the surface of the steel - note tack weld marks running the circumference of the oval shaped can - there are two inner rows outlining the center section, dividing the can into thirds roughly.

I started the project with a sheet metal saw (like a small sawzall), but found later that a thin metal cutoff wheel on a handheld grinder worked way better. Pick a line to the *inside* of the line of tack welds and cut the can in half. I chose to cut close to the tack welds on both sides, sectioning the entire center section out in two cuts.

At the half-way mark, I dug out all the fiberglass and steel wool - it will make a huge mess when you work around it, and mind you don't breathe the dust that clouds up when you pull it outta there.

Cut and trim the edges until you have cleaned up the sectioned can, creating two separate smaller muffler cans. These still have muffle material in them, so they will still quiet your exhaust down a bit. You can see it in the two "top" 1.5" ports. The other two ports are mainline dumps from the engine-side. One of these gets covered up and the other (closer to the center) gets cross-connected with the 1.5" tubing.

The perforated pieces simply keeps the fiberglass material from blowing out your exhaust tips, so get out that grinder and cut the welds. This will reveal the two large 2.5" ports, along with a tiny one in between. Sorry I couldn't find a clean pic of this stage.

At this point, I chose to weld the entire seam at the point where the newly cut shell and the inner section wall come together. This looked like a place for exhaust to leak out or vibration to occur. This pic shows the crossover already in place, but you can see the outer seam is welded. You can also see the patch I welded over one of the smaller 1.5" ports - I re-used some stainless sheet from the center section for this.

Next Post: making up the center section & test fitting, measuring, test fitting, measuring, test fitting...

11-26-2011, 12:36 AM	#1 (permalink)
nismolife Base Member Join Date: Oct 2009 Location: Everett Posts: 24 Drives: 09 Nismo 370Z Rep Power: 15	DIY - Modified NISMO Exhaust - better sound, better power I've seen a lot of threads out there asking if a Nismo exhaust could be modified to at least make it louder and possibly improve it. I couldn't find any real attempts to mod a 09 Nismo can, so I decided to try it. My fall back plan would be to just buy a FI setup, but I wanted to try my hand at it first just to satisfy my curiosity. Note that stock non-Nismo muffler cans may be a bit different, but I'm betting that they are all similar enough to do this mod. I finished the project and I really like the results. The sound is quiet at idle, but livens up quickly as you get on it. There is no drone or nasty rasp whatsoever. I didn't dyno it, but the Nismo is doing some things I'm not used to - like breaking loose on dry pavement at 40mph (2nd gear, throttle only), or 70mph in the wet. Definitely no loss of torque, and the butt-dyno says maybe a small increase was found. Update: I attempted to record some videos and found out my new phone (HTC HD7) actually has noise cancelling, which does a great job of eliminating the exhaust sound from the video! I'll break out my GoPro cameras & see if I can do better. The 09 Nismo muffler can has 3 internal chambers. The main exhaust dumps into the center section, mixes, and then exits back out side sections. There are two 2.5" ports in each side section to allow for this flow. There are also a number of other smaller ports dumping into the center section, presumably for tuning the sound(?) In this mod, I decided I would create a better flowing crossover pipe that joins the two sections, hopefully getting better sound without a loss of torque. The crossover pipe is made of 14 g stainless exhaust tubing from Summit Racing, in 3" and 1.5" sizes Summit Racing SUM-640130 - Summit Racing® Stainless Steel Exhaust Tubing - Overview - SummitRacing.com. I'm a novice welder, so this was my chance to go buy some stainless mig wire & get some practice welding stainless. You need (1) of the 3" and (1) 1.5" piece of the stainless tubing. First, a tip on removing the axle-back muffler can section - crack all four exhaust flange bolts loose first, before taking them off. I did them right-to-left and by the time I got to the last one, there was enough force pulling against it that the nut stripped and I ended up having to cut the welded bolt off the flange in order to remove it. Shoot some penetrating oil on them as well before attempting to take them off. I couldn't reach these bolts with an impact, so I had to reef on them with my socket wrench, which probably contributed. After loosening the four main flange bolts, find the bolts holding the mounting brackets to the body - on my car, there were 3 bolts on each side holding triangular steel flanges. Careful with these too, because as they come out, the weight of the muffler section starts to put stress on them - you could end up having trouble with these also - especially take care when replacing them. The idea is to remove the mounting plates - not to try to pull the brackets out of their rubber vibration-isolators. The mounting plates and rubber isolators will just hang off the muffler pieces until you mount it all back up again. Assuming you aren't still busting your knuckles to get the muffler section out, have a look at the surface of the steel - note tack weld marks running the circumference of the oval shaped can - there are two inner rows outlining the center section, dividing the can into thirds roughly. I started the project with a sheet metal saw (like a small sawzall), but found later that a thin metal cutoff wheel on a handheld grinder worked way better. Pick a line to the inside of the line of tack welds and cut the can in half. I chose to cut close to the tack welds on both sides, sectioning the entire center section out in two cuts. At the half-way mark, I dug out all the fiberglass and steel wool - it will make a huge mess when you work around it, and mind you don't breathe the dust that clouds up when you pull it outta there. Cut and trim the edges until you have cleaned up the sectioned can, creating two separate smaller muffler cans. These still have muffle material in them, so they will still quiet your exhaust down a bit. You can see it in the two "top" 1.5" ports. The other two ports are mainline dumps from the engine-side. One of these gets covered up and the other (closer to the center) gets cross-connected with the 1.5" tubing. The perforated pieces simply keeps the fiberglass material from blowing out your exhaust tips, so get out that grinder and cut the welds. This will reveal the two large 2.5" ports, along with a tiny one in between. Sorry I couldn't find a clean pic of this stage. At this point, I chose to weld the entire seam at the point where the newly cut shell and the inner section wall come together. This looked like a place for exhaust to leak out or vibration to occur. This pic shows the crossover already in place, but you can see the outer seam is welded. You can also see the patch I welded over one of the smaller 1.5" ports - I re-used some stainless sheet from the center section for this. Next Post: making up the center section & test fitting, measuring, test fitting, measuring, test fitting... Last edited by nismolife; 12-05-2011 at 10:06 AM.