The early '70s marked the end for free-flowing muscle cars. Pontiac was forced to detune its products, cutting back on horsepower and choking performance—especially with exhaust. Pontiac estimated the original 400 in our latest '72 GTO project at 250 hp when it was new. "Now, we're well over 400 hp," said Bobby Ellis with Family Automotive in Canoga Park, California, who built this Goat's new 400 with Edelbrock heads and 10:1 compression. More power means more exhaust.

Now we weigh our options. We can visit the local muffler shop for a custom system, but that can be expensive. Instead, let's do it ourselves, but like many of our readers, what if we don't have a pipe bender or welder?

We called our friends at Pypes Exhaust for its ready-to-bolt-in A-body kit. Pypes' pre-mandrel-bent, vehicle-specific kit uses 409 stainless steel, 16-gauge pipe, and costs around $500. Including everything you need for a quick insulation, it's designed for the pipes to easily slide into each other, requiring only handtools to put together—perfect.

Pypes recommended we use its 2.5-inch exhaust kit (the A-body kit is available in 2.5- and 3-inch diameter). "Most V-8s are happy with 2.5-inch. With that, you'd be able to control the decibels inside the car," said Brandon Tscheschlog, our go-to tech at Pypes. The larger pipe, the higher chances you have interior drone. Pypes recommends 3-inch if you're making over 500 hp or if your Pontiac is more race and less street.

All of Pypes' application-specific kits offer your choice of three mufflers: Violator, Street Pro, or Race Pro. We chose the Street Pro mufflers, the most efficient of the three options. "…A good street muffler with a nice muscle-car tone, but it won't wake your neighbors," said Brandon.

We loaded the GTO on the lift, but you only need four jackstands, handtools, and a friend to convert your Pontiac to rumbling exhaust in an afternoon.

Pypes Performance X-pipe kit for A-bodies retails for $369.89 (PN SGA10). We opted for the Street Pro mufflers (PN SGA10S, $126.13) and collector reducers (PN PVR19S, $75.08) for a total of $571.10. The kit uses mandrel-bent, stainless-steel piping and includes everything we needed for the install.

1. Bobby Ellis with Family Automotive in Canoga Park, California, helped us install the kit.

2. It was fairly easy to drop the 2-inch piping that had been done by a custom muffler shop some time ago.

3. We removed the old hangers one at a time and replaced them with the new ones included in the kit. We did as much work here before he had to lift the heavy exhaust over our heads.

4. Here is the new A-body exhaust hanger compared to the old one.

5. The A-body-specific hangers are directional and bolt in with new hardware included in the kit.

6. We removed the old hangers under the quarter panels and behind the rear axle, but made a mental note of where they mounted. Oftentimes there are multiple mounting holes in the factory framerails for exhaust hangers.

7. We knocked the bolt with a hammer since we weren't using the old hardware or clip anymore.

8. Pypes includes three pairs of different-style hangers. We opted for the shorter tailpipe hangers here, but in a different factory frame hole (closer to the rear bumper), because we are going to run a dual-tip exit under the bumper.

9. With the hangers bolted in, we can start installing the piping. The bend over the rear axle can be the most problematic part of any exhaust system. Pypes says to start from the rear and make your way forward. This way, if you have any fitment issues, you can trim a straight piece without messing up the important mandrel bends.

10. Here we use our supplied clamps to mount the exhaust in place, but keep them loose until we are finished with the installation.

11. We selected the mid-range Street Pro mufflers because they offer a muscle-car tone without putting us on the violation side of the law.

12. Bobby held the rear-section and muffler in hand as we handed him the clamp and hardware to bolt them to the new A-body hanger.

13. The X-pipe kick will add torque and reduce that annoying popping found with exhausts that have no crossover, while still clearing our driveshaft and transmission. “Our kits are designed as transmission-crossmember back and should clear four-speeds, five-speeds, and even GearVendor units,” said Brandon.

14. With the exhaust system in place, we slid it against the headers, with one of us holding the piping and the other bolting it in place. This is the moment you'll find out if you need to trim the length of the system or do any modifications. Luckily, we had no issues.

15. We finished bolting the headers to the exhaust system using the supplied hardware and gaskets. Most header kits include extensions for the exhaust to mate with the collectors, but our 400 had Hedman Headers long-tube headers with 3-inch collectors, so we ordered the 3- to 2.5-inch primary Collector Reducers from Pypes (PN PVR16S, $71.61).

16. Almost done! Our system is installed with all of the clamps loose because they are designed to crimp the pipe and it's not ideal to remove them after tightening. Here we made sure the system looked snug without resting against the floor or axle, shifting pipes as necessary.

17. Now that the system is installed we began to slowly tighten the clamps evenly. We angled the clamps away from the ground.

18. The mandrel bend over the axle is hard to do, but we had our entire system installed within two hours. If you run into any problems with the pipe dragging the axle, you can trim one of the straight pipes ahead of the bend. We didn't need to.

19. Here is the completed exhaust without tips. The system is a true dual that exits on either side under the bumper. In stock form, the '72 GTO had side exits behind the rear tires with dual tailpipes on both sides. Pypes is working on an addition to the kit to allow for a factory-appearance exit. Now our high-compression 400 can breathe.

Pypes Performance Exhaust
2880 Bergey Rd
PA  19440