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The Flowmaster exhaust for '98-02, V-6 F-Body cars. |
The inlet is at the lower left. | 
Before you begin, paint the muffler and front pipe/resonator assembly. |
Sometimes when you're looking for story ideas, the best bet is to go straight to the aftermarket manufacturers and find out what calls are jamming their tech lines. Often, it's for parts and installs that haven't even hit the market! According to Flowmaster's Marketing Manager, Bryan Moberly, their company's most requested new product was an after-cat exhaust system for V-6-powered Chevy Camaros and Pontiac Firebirds. Who knew?
Figuring that indicates interest in hot-rodding those cars, we acquired a '01 Camaro with a 3.8L V-6 five-speed manual powertrain and tried a few mods. The first was Flowmaster's new American Thunder after-cat exhaust system (PN 17358) for '98-02 GM F-Body cars with the "3800" V-6 engine. When you open the box, you see larger-than-stock, 2.5-inch aluminized pipe, an 80-series muffler and stainless-steel-tipped exhaust outlets. All that is typical of Flowmaster exhausts, but one unusual feature, is the small resonator Flowmaster adds to the V-6 F-Body car system. Cleverly packaged, it occupies an unused cavity under the car, beneath the passenger-side rear seat. Flowmaster Engineer, Kevin McClelland, told me that certain frequencies of V-6 exhaust noise are difficult to attenuate and this resonator, which a stock exhaust doesn't have, is a strategy for doing that.
The American Thunder exhaust for V-6 F-Body cars worked on the DynoJet chassis dyno to the tune of almost 11 hp at the rear wheels, which is nearly a seven percent improvement. Using a Vericom VC2000 Performance Computer, an on-board, vehicle dynamics testing device (www.vericomcomputers.com), we observed an improvement in 0-to-60 time from 7.83 to 7.44-sec. and quarter mile stats going from 16.15 at 89.14 to 15.87 at 90.69. That's pretty darn good for just doing an exhaust change. It also shows the stock exhaust, even the dual-outlet system that came with our Camaro's "Y99 Sport Handling Package" is pretty crummy.
The American Thunder exhaust can be installed in an afternoon, using hand tools, and the car on jack stands. Unfortunately, we had some problems with the system's fit. One of the tailpipes contacted some underbody structure and the positioning of both pipes under the rear bumper wasn't right. Upon discovering this after our DIY installation, we had Gene's Mufflers in Downey, California (which had an acetylene torch, a tubing bender and a lift) re-do the installation and, in the process, slightly modify some parts to solve those problems. In Flowmaster's defense, the exhaust system we received was the first one manufactured. With production tooling and quality control measures, they will have eliminated the few problems we had by the time you read this.
While we welcome the extra performance, we also enjoy the Camaro's new sound. Stock exhausts on V-6 F-Body cars are too quiet, too "blatty" and have ugly tail pipes. Flowmaster fixed all that. While it's called American Thunder, we'd characterize its sound not as thunder in an obnoxious manner, but with that sweeter-deeper tone all Flowmaster exhausts seem to have. The appearance of the stainless steel outlets along with the angle and length of the pipes are a big improvement, too.
To get the stock system off, cut it in two places, just ahead of the rear axle and where the over-axle pipe connects to the muffler. A hacksaw works okay, but a power grinder with a whiz-wheel, or a "Sawzall" is best. | 
You have to drop the Panhard bar mount brace down low enough to get Flowmaster's over-axle pipe into place. If you're doing this on your back, move this brace even before removing the stock "over-axle" pipe. Remove the two screws holding the fuel tank shield to the brace, and then the three bolts on the driver-side end, loosen the bolt on the passenger-side end, and drop the brace down. Then, snake the Flowmaster pipe into place and rest it on the rear axle. |
Next to go on, is the front pipe and resonator assembly. An exercise in ingenious packaging, the Flowmaster resonator occupies a cavity formed by the passenger-side rear seat. The positioning of the resonator case in this cavity is critical as it just barely fits and, if it's not in the right spot, it will contact the underbody as the powertrain moves. Use your fingers to gauge the clearance in front and in back of the resonator. | 
Getting the clearance right may require moving the assembly fore or aft on the slip joint. Also, the resonator needs to parallel the chassis' horizontal plane. Once the resonator is positioned, snug but do not fully-tighten the clamp holding it to the catalytic converter outlet. Once the entire system is mounted, you may need to move that joint again. When the installation is complete and the whole system is properly positioned, then tighten the clamps. |
Put the over-axle pipe in place. Again, you want to snug, but not fully-tighten the clamp so you can, if necessary, reposition it later. Re-install the Panhard bar mount brace and the fuel tank shield screws. Unseen, towards the end of the over-axle pipe is an exhaust hanger prong that goes into the stock hanger on the frame rail above the pipe. | 
Some Flowmaster systems will use clamps like this. In order for them to "bite" hard enough on the joints to hold the pipe tight; we scrapped Flowmaster's flange nuts and replaced them with hardened, double-thickness flat washers and hex nuts. This way when you tighten the nuts, they won't just deform; they'll tighten the clamp. |
A correctly positioned over-axle pipe looks like this. The arrows point to two critical clearance areas: the spot (left arrow) where the pipe passes between the Panhard bar mount brace and the exhaust shield and a second tight spot below the exhaust shield and just behind the pipe's second major bend (right arrow). | 
The first time we did this (on a trial fitment), we had to hold the muffler up in place while we slipped it onto the over-axle pipe and attached it to the hangers. The second time, Greg Toats did it easier with a muffler jack (the pole to his left). Once the muffler is in place, don't fully-tighten this clamp (just get it snug). The rotational position of the muffler on the over-axle pipe controls the angle of the tailpipes, as does the position of the tailpipes in the muffler. Once both pipes are on and the hangers installed, you'll probably have to rotate the muffler and/or rotate the pipes. Gene's Mufflers modified the system slightly to correct the tailpipe outlet position problem we had. The final bend in the over-axle-pipe was such that the muffler's axis wasn't 90 degrees to the car's longitudinal axis. That had one pipe sticking out an inch farther than the other. Greg Toats, installed the muffler, snugged the clamp, heated the joint with the torch, then pulled back hard on the muffler to bend the joint. That moved the left end of the muffler back, putting the muffler at right angle to the car's axis and properly positioning the exhaust outlets. |
The other problem we had, involved the passenger-side tailpipe contacting the outside of the spare tire well in two places when the car was making left turns. To fix the tailpipe interference problem, we bent the two hangers (arrow shows right-side hanger), which moved everything left and away from the underbody. However, bending the hangers had the muffler hanging with the left side low (other arrows) so, Greg Toats used his tubing bender to tweak the bend in the right tailpipe so the pipe had more clearance from the underbody. Greg "unbent" the exhaust hangers, then re-installed the left tailpipe. | 
The result was a tailpipe pipe that didn't contact the body and a muffler that hung level. The wood block was used to force the left side of the muffler rearward while Greg applied heat to the joint between the over-axle-pipe and the muffler. It was left in place until the joint cooled and all the clamps were tight. |
If you think the Flowmaster American Thunder exhaust looks good, it works even better. We gained almost 11 hp and almost three-tenths of a second in the quarter mile. | |
QUICK HOP UPS FOR YOUR V-6
We were so smitten with the results of our first mods to this V-6 Camaro, we tried some other stuff, too. Dynamically, all of this stuff adds up to significant gains, both at the rear wheels and at the seat of your pants. From stoplight to stoplight, you and your victims will tell the difference!
We added a set of colder ACDelco spark plugs (PN 41-919), a double-platinum-tipped set that some Corvette tuners have told me are amongst the coldest (it's a hedge against detonation during dyno testing and WOT road testing). A Goodyear "Gatorback" Poly-V belt (PN 4060940) with a unique diamond-checked surface that allows it to run up to 15 degrees cooler, extending belt life, too. Swapping to a Stant 180-degree thermostat (PN 45848) lets us get a little more aggressive on spark timing and it improves durability of under hood rubber and plastic parts (down from the stock 195-degree unit).
A whole host of Red Line Synthetic lubricants makes for real gains at the wheel, (as almost every magazine has proven in testing). We put 10W30 engine oil in the V-6, power steering fluid in the steering, D4 ATF in the Tremec five-speed and 75W80 gear lubricant in the car's Torsen-equipped, 7.5-inch axle. The performance gain was slight, but we went with the Red Line products mainly for the improved durability they offer to powertrain components that see severe duty, and the option of using an extended oil drain interval of up to 16,000 miles.
We completed our modifications by altering some of the engine computer's basic controls, using a HyperTech Power Programmer Plus (PN 30009). We used this unit to alter our PCM's fan-on temperatures to better match the 180-degree thermostat, to alter the vehicle speed limiter above stock with T-rated tires, optimize the speedometer calibration for the slightly shorter Goodyear F1 GS-D3s, and make the spark curve slightly more aggressive. The PPP+ has two spark calibrations, one for 87-octane fuel and one for 93-octane fuel. Since 93-octane fuel is not generally available in the western U.S., we opted for the 87-octane "cal."
Swapping the original-equipment tires, a set of T-rated Goodyear 235/55R16 Eagle GAs, for a set of Goodyear 245/50ZR16 Eagle F1 GS-D3s, made a huge difference. Swapping for new rubber might be the most noticeable change in how your car drives and, seriously, not enough people consider it first as a performance change. The Eagle F1 GS-D3 (www.eaglef1.com) is Goodyear's newest ultra-performance radial. It is positioned between Goodyear's super-dry-traction, F1 Supercar and the F1 GS, the OE tire on the base Corvette, the Mustang Cobra and Camaro Z28SS. It has very good dry traction and, by virtue of its rather unusual tread configuration, outstanding wet traction. It is one of the best all-weather ultra-performance tires on the market right now and works quite well on our Camaro.