JNZ Tuning Down Pipe Review

I finally finished editing my video that shows the sound difference between my prior setup and now with the main Cat replaced with the Down Pipe. So I figured I’d take this opportunity to write a full review of the product since I was the first to install.

As you can see from the pictures, this is a really high quality piece. The welds are great and it’s also 8.2 lbs lighter than the stock main cat. The pipe comes with new gaskets for the header side and the cat-back side as well as new hardware for both ends as well (2 Bolts, 5 Nuts, 5 washers)

All 17mm. Installation was done with the car on jack stands and I only removed the under panels to get to the pipe. So here’s how to install it (NOTE: Your results may vary. Follow these instructions at your own risk.)…



Tools Used:
4 Jack Stands
Floor Jack
Air Ratchet 3/8” Drive (Because I’m lazy and I have the tool)
14mm Deep well socket
17mm Socket
10mm socket (for the under panel. I also used a hex wrench, but I have the C-one panel so I won’t go into it too much)
6” ratchet extender
3” ratchet extender
3/8” Drive Ratchet
1/2” Drive Ratchet and 1/2 to 3/8 reducer (Used so I could get the damn O2 sensor out)
O2 Sensor Socket
Flat head screw driver

Step 1 — Jack up the car and put it on stands using the correct jack points. Get it as high as you can so you have room to work. I raised one side about half way up, put stands on that side, then did the other side so I wasn’t jacking up a steep angle.

Step 2 — Remove both Under Panels. These are all you need to remove. You can access everything from underneath the car.

Step 3 — Using the 14mm socket and either ratchet or air tools, remove the 3 nuts holding the main cat to the header. If this is the first time you’re taking these off, you may need to soak your nuts in PB Blaster or something. Mine came off easy, but that’s because I installed Che’s header not too long ago.

Step 4 — Using the 17MM socket and either ratchet or air tools, remove the 2 bolts holding the main cat to the cat-back exhaust. These may be VERY rusty And it’s a good possibility you’ll snap one. Mine came out fine, but that could be because I installed the TRD exhaust a couple years ago. When doing that install, one of the bolts snapped off. Anyway, once you get those bolts out, the only thing really holding the cat to the car is the hanger. The cursed hanger.

Step 5 — Remove the O2 Sensor. Using the O2 Sensor Socket, loosen the Sensor so that you can use your hands to unscrew it the rest of the way. I had to use my beefier 1/2” drive ratchet to get this thing loose. But it came out fairly easy. Let it dangle down, but try not to bump into it.

Step 6 — Spray some WD-40 on the metal rod that the hanger goes on where the 2 meet. You need to lube that area up real good. There is no easy way to describe how to get this off. It will be a PITA and possibly the longest part of the install. Use the flat head screw driver to wedge in between the rubber hanger and the metal rod connected to the car. If you can get it all the way through, push up on the handle to try to work the edge of the rubber over the mushroom head portion of the metal rod. Once you eventually get that damn thing off, the cat should come down. I wiggled mine around for a while as it was just hanging down by the rubber hanger. This step took me a LONG time to do. Once you get it off, take the rubber hanger off of the main cat and put the hanger back on the car by itself.

Step 7 — Take your gaskets that came with the down pipe and make sure everything lines up on your setup. I needed to make some modifications to mine, but I talked to greenstreak on the phone and he was going to modify the others to make sure other people don’t have the same problem. If they all line up properly, then you’re good to go. Push the hanger rod through the hole in the rubber hanger and get to bolting and screwing.

Step 8 — Start with the cat-back side. put the gasket between the down pipe and the exhaust and thread one of the 17mm bolts with a washer on it through one of the holes and into the exhaust. Do the same on the other side. Don’t torque them down just yet.

Step 9 — Now do the header side. put the gasket between the down pipe and the header and make sure it’s lined up and push it up so the studs come down through the holes on the down pipe flange. Now just thread a washer and 17mm nut on each stud.

Step 10 — If everything is all hooked up and looks good, torque the nuts/bolts down to spec. I used 38 ft-lbs for the cat-back bolts (The stock setup has springs and other things going on so I discussed the torque specs with greenstreak on the phone before arriving at 38. Torque the header nuts down to 36 ft-lbs.

Step 11 — Re-Install the O2 Sensor. Use your hands to thread it in and then use the O2 Sensor socket to tighten it to 32 ft-lbs. I just tightened it good without using my torque wrench. I’m only reporting what “the book” says.

Step 12 — While the car is still up on stands, Start it and check for exhaust leaks. I didn’t find any which is good. You shouldn’t either, but you should always check to be sure.

Step 13 – If all is good, put your under-panels back on and drive! When you get back, put away your tools and relax with a cold beverage.

Here’s a couple pics of it installed:



Now before I get to the before and after results, let me mention my mods at the time of install that would affect sound or power:
Injen Intake
Che Header
TRD Cat-back exhaust
Fidanza Flywheel
A’pex-i PowerFC

I did not re-tune or change anything with the PFC before, during or after the install. The gasoline used was from the same Chevron station that I always go to. The tests were done on different days, but the weather was nearly identical. Gas level was at 1/4 tank during “Before” measurements and was at 1/2 tank during “After” measurements. For more information on weather and other factors, visit the GB thread on SpyderChat where I listed the weather conditions on both days. Also remember that the G-Tech always calculates HP lower than it really is.

Here’s a G-Tech Dyno of a before and after (Red = Before, Green = After):


I had a measured gain of 10.5 WHP and 9.5 ft-lbs after installing. Largest gains were at the top end, but the bottom end didn’t suffer. It was simply better throughout the whole RPM range.

Here’s a video I put together noting the changes in sound. Remember that the before sections still have the above mentioned mods.
Down Pipe Video -> DownPipe.wmv

It’s louder, but not much louder than it was. I was very worried that it would sound rice-tastic. I’m glad it doesn’t. Let the video help you hear the difference and you can decide for yourself. Overall, I’m very happy with the product and the results. I hope this review is helpful to those who also purchase this item.

I got mine with the extra bung for the WB O2 sensor. But I haven’t hooked that up yet because I wanted to do an apples to apples comparison. Plus, I’ll need to do some wiring to get that done and I didn’t feel like getting into that this weekend.

After driving around with this down pipe, a design flaw/defect came to be known.  The place where the exhaust flange meets up with the cat-back exhaust did not seal well at all and caused exhaust leaks.  After this was brought to Greanstreak’s attention at JNZ tuning, a new design was produced.  I had to buy the new design to replace my flawed piece.  The first one that came had better connections, but hung way too low below the cross-member and you could not install under panels.  So that was replaced at partially my expense for another one that was better, but still not right.  I decided to cut my losses at this point and make the 3rd one that I was using work with my setup by modifying some other brackets and attachment points of my C-One under panels.

So, if you are going to purchase one of these, check to see what their return policy is and ask what version of the piece you are getting.  It does make great power.  But the fit is not perfect.


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