Muscle Mustangs & Fast Fords
1990 Thunderbird Super Coupe - Birds Of Prey - Tech
Super Coupe Performance, With Bird Basics.
Compared to the 300hp Mustang GTs and 500hp Shelby GT500s, the specs of a '90 Thunderbird Super Coupe seem pretty tame. Back in the day, however, the supercharged 3.8L was a pretty heavy hitter. Though down on displacement, the 3.8 thumped out nearly as much power as the 5.0L Mustang (210 hp versus 225 hp), and torque production was equally impressive, with the supercharger helping to up the twist to a V-8-like 315 lb-ft of torque. The impressive torque curve is why the Super Coupes offered such impressive acceleration. With a peak power output that occurred at just 4,000 rpm and torque peak some 1,000 rpm earlier, these motors offered diesel-like torque curves.
Unfortunately, placing the emphasis on the impressive low-speed power production meant the supercharged 3.8L was not rev-happy. There was little sense in revving the motor to 5,500 rpm or beyond since the peak power occurred at just 4,000 rpm. On the plus side, the Super Coupe offered an impressive combination of ride quality, handling, and braking (given the hefty curb weight).
Super Coupe owners are intensely loyal to their chosen mount, and they should be. It's a great-looking package and without a doubt much more aerodynamic than many other cars of the time. If you're looking to go fast (as in Bonneville fast), the T-bird is a much better package than a Mustang. Aesthetics aside, the real reason to own a Super Coupe is because it sports forced induction.
Any motor that comes from the factory with a turbo or blower will always provide plenty of additional performance with some tweaks. The easy route is to simply turn up the boost, but as we found during many sessions on the chassis dyno, there's more to the performance equation than what's indicated on the boost gauge.
Given the flow limitations of the small M90 supercharger employed by Ford on the 3.8L, it would take more than just a smaller blower pulley for us to drastically enhance the power of the '90 Super Coupe. We've heard of modified Super Coupe motors exceeding 300 rwhp, though we've yet to verify the claims.
Naturally, the first order of business was to establish a baseline. The five-speed Super Coupe was taken to the Super Flow chassis dyno and run in bone-stock trim. The virgin motor (meaning high mileage but no performance modifications) ran well despite being nearly 16 years old and having logged over 180,000 miles. Rated at 210 flywheel horsepower, the stone-stock T-bird belted out power numbers of 192 hp and 265 lb-ft of torque with a peak boost reading of 11.9 psi. Literature from Ford indicates the motors were supposed to run 12 psi, so it looked like our little 3.8L was still running strong.
As expected, the torque curve was broad, peaking at just 3,000 rpm. Torque production exceeded 200 lb-ft, from 2,000 rpm to 5,000 rpm. In the meaty part of the curve, the torque production exceeded 250 lb-ft, from 2,300 rpm to 3,400 rpm. The stock motor wouldn't rip off your head with accelerative forces, but it still managed to get the big car moving onto the local freeway with vigor. It's not ready for a spot on Pinks, but neither is it ready for the slow death of the wrecking yard.
With our baseline numbers repeating nicely, we ventured into Super Coupe performance land. Starting at the beginning, we replaced the stock flat-panel air filter with a K&N unit. We all did this to our 5.0L Mustangs back in the day, and for good reason. The factory filter was pretty dirty, and replacing it with the free-flowing K&N filter netted an impressive power gain. It must be stated that we did not have access to the usual array of data-logging equipment for this dyno session and had to rely on the factory tempera-ture gauge to ensure we started each run at (or near) the same coolant temp.
After replacing the stock filter with the K&N, the power jumped from 192 hp and 265 lb-ft of torque to an even 200 hp and 287 lb-ft. As always, we included graphs to properly illustrate the power gains, since peak numbers tell only a small portion of the story. The new filter added sizable gains in the low and midrange, but little or no power at the top of the rev range. We suspected that some of the torque gains could be attributed to a change in temperature between the runs, but a back-up run (with the stock filter) brought us back to the original power numbers. We guess the K&N panel filter is a worthwhile upgrade on the Super Coupe, especially since it ensures cold air to the motor when the hood is closed.
Having improved the inlet flow of the system, we decided it was time to crank up the boost. This was accomplished by replacing the factory blower pulley with a 5 percent overdrive pulley from Super Coupe Performance. Bill at Super Coupe Performance was instrumental in getting this T-bird project off and running. Replacing the pulley required removal of the pressed-on factory pulley. Bill supplied a removal tool (basically a backing plate to be used with a three-jaw puller) that made short work of the pulley swap. After the installation of the smaller blower pulley, we were rewarded with roughly 1.5 psi of extra boost and a sizable chunk of torque to go along with it. The supercharged 3.8L had now officially cracked the 300 lb-ft barrier, with a peak torque reading of 309 lb-ft. Torque production exceeded 300 lb-ft from 2,100 rpm to 3,200 rpm and didn't drop below 250 lb-ft until 4,300 rpm, but we were just getting started.
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With the blower now making more boost, we turned our attention to the inlet system. After we had such good success with the K&N filter, we looked at the small factory mass airflow meter (MAF). A call to C&L netted us a 73mm meter along with a free-flowing cone filter. Being a true bolt-on performance piece, installation was easy, and we were up and running in no time. The C&L improved the peak power output to 211 hp at 4,100 rpm and torque production was now up to 315 lb-ft at 2,800 rpm. The larger MAF added power throughout the rev range, but was most effective near the top (where the additional airflow would be most useful). With plenty of inlet flow available to the supercharged motor, we once again stepped up the blower speed. This time we employed a 5 percent overdrive idler pulley, as the Super Coupe motors rely on a secondary idler (driven off the crank) to provide drive to the blower. Increasing the blower speed via the revised idler resulted in a jump in peak power to 216 hp, but the torque gains were as high as 12-15 lb-ft through most of the curve. The extra 1.5 psi of boost was especially beneficial from 2,000 rpm to 3,600 rpm, where the 3.8L pumped out more than 300 lb-ft of torque.
With the motor now producing 216 hp and 327 lb-ft of torque, we took one final shot at our bird of prey with a Flowmaster after-cat exhaust. In addition to the free-flowing exhaust system, Flowmaster also supplied a new resonator. The combination proved to be quite effective as it improved peak power output to 230 hp and 332 lb-ft of torque. Unlike the previous mods, the majority of the power gains occurred higher in the rev range, though the Flowmaster exhaust system did offer additional power as low as 2,300 rpm. While we're still not near our goal of 300 hp, we're making gains, and perhaps we'll continue the hunt in future issues.