Flowmaster Exhaust – Perfect 3″ G-body exhaust

So you think your exhaust system is just a bunch of pipes? WRONG! They can be a work of art just like the rest of the car… The Project: “HotRodRegal” now has the perfect 3 inch stainless steel Flowmaster exhaust system. Follow along as my friend Greg Cragg and I install a garage built, Flowmaster 3 inch stainless steel universal kit (Part # 815937) with the Flowmaster 3 inch stainless steel scavenger X-pipe kit (Part # 815933) for a compact, modern looking, high flow exhaust system. This system combined with the Ultimate Headers 3-bolt stainless steel collector flanges, makes for an awesome “SEMA quality” exhaust system.

Cool, and compact. The FLOWMASTER exhaust kits were designed to work with other exhaust components for a custom installation.
Cool, and compact. The Flowmaster exhaust kits were designed to work with other Flowmaster exhaust components for a custom installation.

It all started with receiving one of the first sets of Ultimate Headers for the G-body LS engine swap. (see my article: Ultimate Headers = Ultimate G-Body).

The Ultimate Headers for the G-body LS swap
The Ultimate Headers for the G-body LS swap

I wanted to keep the quality level of the exhaust system very high. I called up Flowmaster because I was familiar with their high quality parts and their classic aggressive sound. I worked with some very helpful people at Flowmaster when I called, and we were able to come up with a complete parts list that would produce the type of exhaust system I had planned. During our conversation, I explained I had not built an exhaust system before and stated a list of criteria that I wanted in the exhaust system.

My exhaust system criteria included:

  1. Stainless steel construction
  2. 3 inch diameter
  3. Tail pipes that exit behind the rear tire at a 45 degree angle
  4. X-pipe
  5. Electronic Cut-outs to be added
  6. Mufflers that have an aggressive sound when needed, but still able to carry on a conversation in the car at highway speed

The folks at Flowmaster were very helpful with explaining how to build an exhaust system that would incorporate everything I wanted. At first the Flowmaster representative informed me about the American Thunder 2.5 inch diameter stainless steel kit for the G-body.  While this was a very cool product and would meet most of my needs, I really wanted a 3 inch diameter system for sound quality and eventual power enhancements. Also, I really like the tail pipes on a G-body to exit at a 45 degree angle. The only way to obtain these qualities is to order the 3 inch universal kit. The following is a diagram of the parts included in the 3″ stainless steel universal kit and how I used them


There were enough parts in this kit to configure the exhaust in several different ways. The Red and Green notes indicate how I used this kit.

The universal kit comes with provisions to create an H-pipe style exhaust.  The H-pipe actually works better for engines that make less than 600 Hp and a 2.5 inch stainless steel pipe will create more bottom end torque than a 3″ pipe at 600 Hp level and below, but I wanted to build a system that would be able to incorporate future power increases. I added the 3″ scavenge X-pipe kit to my order so I could add electric cut-outs from Race Ready Performance (more on the cut-outs in future articles). The following is a diagram of the 3″ scavenge X-pipe kit and how I combined it with the universal kit.

815933 x scavange pipe
The 3 inch stainless steel scavenge X-pipe kit from Flowmaster provides torque improvement in high horsepower applications. I like the modern appearance and the fit of the crossover.

Before any exhaust work was performed, we built blocks to raise the project: “Hot Rod Regal” up off the ground. The exhaust kits from Flowmaster could easily be constructed and welded under the car at this height.

To begin work under the car, Greg and I built these 2x4 blocks to raise the car. These work great and I recommend building a set to work in your garage.
It is not possible to build an exhaust system under a lowered car on the ground. So, before any exhaust work was done, Greg and I built these 2×4 blocks to raise the car. These work great and I recommend building a set to work under your car in your garage.

Greg and I began mock up and install in my garage using a Lincoln Electric WeldPak-100 welder I found on craigslist ($200). The Flowmaster parts can easily be positioned under the car and welded with this set up, but our plan was to tack weld the parts together and have them completed by Fish’s Chassisworks.  Neither Greg, nor myself are professional welders, and we wanted a higher quality result than we could perform.

Working from front to back, the collector tubes that connect to the headers were the first parts to be fitted. It was necessary to find the correct bend angles in the pipes to create a system that would be as close as possible to the floor. I did not want to see the exhaust system hanging down below the car. I used one of the 26033S (straight tail pipe) tubes on the driver side seen in the next photo.

26033S is tack welded to the low profile clamp flange from Ultimate Headers on the driver side
Above, the 26033S tail pipe is tack welded to the low profile clamp flange from Ultimate Headers on the driver side
Passenger side with clamp
In the above photo, the Passenger side collector pipe was obtained from Ultimate Headers and had a different angle than the driver side. These pipes were first put together using duct tape, measured, then tack welded to the low profile clamp flanges

The Y-pipes were temporarily installed on the collector pipes and measured for the correct length to clear the cross-member. The collector pipes were then cut to make the Y-pipes dump out evenly behind the cross-member. Once the Y-pipes were in the correct location on the car, I removed them and attempted to fit them to the scavenge X-pipe. The angles did not match up between the parts. The solution was to cut the forward/inlet pipes on the scavenge X-pipe. I found that several pipes would work after this cut, including the angled tail pipe part #26035S.  This solution allowed the Y-pipes to mate perfect to the scavenge X-pipe and was finalized once in the car. Seen in the next photo, the mismatched pipe angles of the Y-pipes and the X-pipe.

I laid out the parts as they would be in the car to better visualize what cuts would need to be made and how things were going to fit together.
I laid out the parts as they would be in the car to better visualize what cuts would need to be made and how things were going to fit together.

The Y-pipes were leveled and visually checked from the side of the car to make certain they were not hanging below the frame.  Once the intake pipes of the scavenge X-pipe were cut and fitted to the Y-pipes, this part of the system was measured and leveled again before tack welding.

Flowmaster tacking x pipe
I found that with every adjustment, the pipes would rotate and it was very important to measure and level the pipes multiple times before tack welding… Here, Greg is tack welding the scavenge X-pipe to the Y-pipes.

Checking for even and level exhaust is accomplished by placing a couple 2×4 blocks on the frame and measuring the distance from the bottom of the pipe to the top of the level. The measurements need to be equal between the right and left sides. Also, due to tight clearances, it is important to fit as many parts as possible in the car to make certain you have the room.  In this next photo, the Race Ready Performance electric cut outs were mocked up with the Ultimate Headers 3-bolt flanges. They fit great! These flanges will have turn down pipes welded to them at a later time that will not have clearance issues.


Continuing aft, the pipes exiting out of the scavenge X-pipe were measured for length before the Flowmaster 50 series mufflers were fitted.

Aft the x pipe
The pipes exiting the scavenge X-pipe have extra length and will need to be cut to fit the Mufflers in the correct location. Also, I modified the floor pans near the bend in these exit pipes to tuck the system up tighter.

During the entire build, it is necessary to support the exhaust system. I used a combination of large Zip ties and blocks of wood to hold the system in place. The Flowmaster 50 series mufflers were the next part to install. The angles from the scavenge X-pipe made this a plug and play situation. The pipes were cut to the required length, and the mufflers were pressed into place. This is probably a great time to mention one of the excellent design features of the Flowmaster exhaust systems. All pipes and components were mandrel bent and expanded on one end to provide a slip fit connection. This makes assembly much easier and ensures a leak free connection.

flowmaster 50 series
The Flowmaster 50 series mufflers are a three chamber design that uses Delta Flow technology along with an internal tuning chamber to reduce sound inside the vehicle. They provide the same performance and exterior tone characteristics as a two chamber, but with less interior resonance. Seen in this photo, the scavenge X-pipe exit pipes are cut to the correct length, the mufflers are slipped into place, and the floor near the bends has been clearanced.

After the mufflers were in place and level, it was time to attack the tailpipe situation. G-bodies do not have a lot of room in the back of the car due to the rear mounted fuel tank and the integral spare tire trunk floor. I personally like the appearance of 3/4 exiting tail pipes vs a 90 degree or a straight exit tail pipe. In the Flowmaster universal kit, there are provisions for each of these styles of tail pipes. Things got a little tight with the 3 inch pipes in this area.

First, up and over the axle. Again, personal preference, but I like the pipes exiting the mufflers to go straight up and over the axle perfectly vertical vs off to the side at an angle. I decided to cut out a little extra frame clearance to accomplish the vertical pipe from the muffler (as seen in the next photo).

frame clearance
This view is looking up just forward of the axle. The extra clearance cut will keep the exhaust pipes exiting the muffler vertically from contacting the frame. Cuts were performed to both sides and dressed.

The process of fitting the 3/4 exit tail pipes took a couple tries. Several trial fits were performed and it was clear that the spare tire trunk floor area was in the way. At first I tried modifying the floor, but ended up cutting the spare tire trunk floor to obtain good clearance for the passenger tail pipe. Keep in mind, this may not be necessary in all applications. I actually wanted to delete this area from the car anyway, and I have future plans for a Taylor Battery Box for this area.

chop chop
I like sawzall’s…
This cut allows for several things to happen. First, clearance for the tail pipe. Second, I intended to modify this area to mount a battery box. Lastly, I have now deleted an area prone to road damage and is an eye sore when looking at the car from the back or side.

With clearances checked and obtained at the gas tank and the spare tire trunk floor, the tail pipes were marked up, double checked and tack welded. In this next image, check out the vertical pipes exiting the Flowmaster 50 series mufflers.

a tail pipe
In this picture, the vertical pipes exiting the mufflers are seen. Now, with the tail pipes in place and clearances obtained, it was time to finish things up by locating mounting tabs for the exhaust system.

On to exhaust hangers. The mounting points on most exhaust systems are predetermined by the factory hangers. Since this has been a frame off, resto-mod build, these hangers do not exist. Also, another consideration, I wanted more attach points to secure the front section of the exhaust system. I chose a weld on stainless steel bracket from Welder Series inc. In the next 3 photos, I show you the locations I chose for the exhaust hangers.

hanger 1
Hanger #1 at the cross-member and connected to the Y-pipes on both sides.
hanger 2
Hanger #2 at the aft muffler flange. These will be connected to body with another hanger in the near future.
Hanger #3 located on the tail pipe and attached to the frame. I had to bend these brackets 90 degrees.

Now that everything was in place, it was time to disconnect everything and have it professionally welded.  The exhaust system was taken to Fish’s Chassisworks for final welding. Check out some of these welds!

Slip fit Flowmaster exhaust pipe welded by Fish’s Chassisworks
Fish’s Chassisworks welded the Ultimate Headers 3-bolt stainless steel flanges to the Flowmaster 3 inch stainless steel exhaust pipes per my request.
Fish’s Chassisworks did an amazing job on all the welding!

Once the welding was complete, the exhaust system was re-installed back into the Hot Rod Regal for a fit check. Everything fit perfect! I am EXTREMELY happy with the way this all came together. The parts fit and look great! The quality is over the top and I am sure everything will perform just as good as they look.

So, this could be the end of the story at this point… but… Nah, where is the fun in that! The complete exhaust system was disassembled (Ultimate Headers and Flowmaster complete exhaust), packed up, and taken to Nashville, Tennessee.  Your going to have to return to www.HotRodRegal.com for the next chapter on the exhaust system. NITROPLATE!!!!

Hope you enjoyed the “Flowmaster Exhaust – Perfect 3″ G-body Exhaust” article and return for more exciting features being added to this exhaust system soon.



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