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Street Race Truck More... The Toolbox

Project Chevelle: Exhaust Tech Article

11/1/2018
From a low angle you can see how nicely the exhaust fits under the car. We've yet to scrape or drag it, which is hard to avoid on a lowered car.

Don't get us wrong, we love the sound of a warmed over small block Chevy through open headers. The first time we fired the 383 in Project Chevelle, it was like a beautiful, deranged mechanical orchestra being conducted right there under our hood. But let's be honest, driving around this way (and we did) can get a little obnoxious. 10:1 compression and 430 horsepower dumping right under your feet is a bit of a sensory overload. Forget about having a conversation with your passengers, and once it all comes to a halt, all that's left is the ringing in your ears. This was really not going to work for a 700 mile road trip.

To solve this problem, we grabbed a Flowmaster American Thunder exhaust system from the shelf. These kits come with mandrel bent, aluminized 2.5" tubing and a pair of Flowmaster mufflers. They also include all the clamps and hangers necessary to install them under any A-body.

If we're being honest, we didn't expect this to be an easy install. In our thrash to prepare the car for its first big road trip, we got to the exhaust at about 11:00 at night. It was late, we were tired. We figured that we would un-box the exhaust system, inventory the parts, lay it out under the car, then go home and go to bed. Amazingly, the install was so simple that we had most of it bolted under the car by midnight.

Installing this hanger behind the muffler is the first step. There are different hangers for 64-67 and 68-72 A-bodies, make sure you get the right one. Also note the steel clips that keep the steel brackets from sliding out of the rubber hanger.

The included instructions had us install the hangers first. There are two sets included, one for 64-67 A-body cars and another for 68-72's. Once these are installed with the included hardware, the rest falls into place quite readily using the supplied rubber isolators and brackets that are already welded to the pipes. I can't emphasis enough how intuitive and easy this process is. Another hanger pair bolts to the framerail behind the axle, and these use self-tapping screws that locate off of holes that are already in the frame. We backed ours up with nuts for added security.

This is the hanger that bolts to the rear framerail. It is married to the clamp that holds the tailpipes on. Make sure the this bracket is oriented properly or the tailpipes will hang way too low.

With everything loosely clamped and hung in place, it was time to build the header reducers. Everyone's header collector situation is going to be different, so Flowmaster leaves plenty of pipe at the front of the system. In our case, we had an old school three-bolt flange on freshly coated headers that we didn't want to cut up. As such, we elected to use some 3" to 2 1/2" reducers that were then welded to the rest of the system. This was the only welding necessary on this install, and this part could be done by an exhaust shop if you don't have access to a welder. This particular install also required a short section of custom bends be welded together to clear the stock transmission crossmember. Most aftermarket crossmembers will have extra room in this area and will not require the extra bends. This piece could also be fabricated at a local muffler shop.

Here's the only part we had to weld. A local muffler shop can make this part for you if you don't have access to a welder.

Otherwise, the rest of the kit is engineered to slip and clamp together. We assembled ours with everything loose to allow us to perfectly position the pipes before tightening them down. Pay special attention to the tailpipes as they pass over the axle and next to the shocks. A little twist can move these a lot and cause the pipe to be touching the shock, gas tank, or floor. Sometimes it works well to use wood or metal scraps as shims in tight areas to make sure the exhaust stays where you want it. The final step is choosing between the straight, slash-cut pipes or the turned-down versions. We chose the turn-downs and love that you can just see them peeking out under the bumper.

Here's the heart of the kit; the Flowmaster mufflers that provide just the right bark to match the new 383's bite.
This shot clearly shows the H-pipe that balances the exhaust pulses and helps to generate a bit more bottom-end torque than a traditional dual exhaust. You can also see how tight the Flowmaster system is to the floor.

Exhaust is tricky to get right. We've all had cars that have smacked the exhaust on the ground every time you go over a bump. Lower the car (as we have) and the problem gets even worse. Once the last clamp was tightened, we were pleased that this kit tucks pretty tight to the floor. Overall, this is a very well engineered exhaust system. But how does it sound?

Here it is all assembled. We love the tips of the exhaust just peeking out under the bumper. Also note the hefty sway bar that, combined with the big exhaust, really makes this car look tough from behind.

Happily, this kit provides a perfect mix of in your face rumble and street-friendly noise control. Stand on the throttle and you are rewarded with a ear-appealing bark from the pipes. Idle around town or cruise down the highway and there's just enough sound to remind you that you're driving a muscle car. At no point is there any obnoxious droning or anything so intrusive that you can't easily carry on a conversation inside the car.

Overall, we're thrilled with this kit. The install, fit, and sound are everything we hoped for. Flowmaster offers these kits for most popular muscle cars. If they all work as well as this A-body kit, we would highly recommend them.

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