1985 Ford Mustang SVO - No Slow SVO - Tech

Moving on, we're now going to chase power in the next logical step by freeing up the exhaust tract. Many folks will tell you that you need some kind of backpressure to make a car run better, especially a turbo car, arguing that a restriction will boost midrange power. On a naturally aspirated application this may be true, but on a turbocharged car, we can't agree. Anytime we've removed a restriction from the outlet side of a turbocharger, there have always been power increases and even torque increases in the midrange. As a matter of fact, the more backpressure we've removed after the turbo, the results have always been positive with more power gained. The only place where you can tune for more torque on the exhaust is by playing with the nozzle (A/R size) of the turbine housing and the manifold or header pipes coming from the cylinder head, leading into the turbo. So, the best bet is to put the largest pipe on the outlet side of the turbine housing you can possibly fit and to run the pipes and mufflers as large as possible to the rear of the car.

Our SVO is still straddled with the original downpipe and quasi-dual exhaust that splits after the hugely restrictive factory catalytic converter. This combination worked marginally well from the factory with its 205hp rating, but our '85½ is already making more than that with just a few bolt-ons (192 rwhp is about 221 flywheel horsepower given a 15 percent drivetrain loss). For our test, we contacted the 2.3L turbo fanatics at Stinger Performance and ordered its 3-inch mandrel-bent downpipe assembly that replaces the entire downpipe and catalytic converter assembly, which then splits into two 2.5-inch pipes to match the dual exhaust of your choice. This replaces the restrictive 2.25-inch factory downpipe and really frees up the engine, allowing it to breathe for more power.

Stinger Performance's downpipe assembly is made from aluminized piping that is mandrel bent for optimum flow. Bolting up to the stock turbocharger's 2.5-inch elbow and swelling to a full 3 inches in size as it goes under the car, it promises to promote all-around performance and give the car a much-needed infusion of sound. The fit was excellent, and all we had to do was connect it to our new Edelbrock after-cat exhaust. We went with the Edelbrock because in our other project cars, we've been entirely satisfied with its deep and mature, but not-too-loud sound. This would be a perfect match for our car because we wanted to inject testosterone to the car's soundtrack, doing away with the wimpy sound that often accompanies four-cylinder cars. Plus, it comes with 2.5-inch mandrel-bent pipes, which are a perfect match for the smooth Stinger Performance pipes upstream.

Although we didn't perform this upgrade, replacing the stock cast-iron exhaust manifold with a tubular header has been a proven part for improved performance. On all '83-'85½ EFI turbo Fords, a cast-iron manifold designed for quick spooling response was known as the E3 casting. In 1986, Ford introduced an improved version (known as the E6 casting) that had a larger outlet at the turbocharger's mounting flange. The E6 is certainly the more desirable factory piece, giving little in exhaust velocity for a much-improved gain in overall flow, resulting in more power all the way to redline. Forced4 offers a really nice tubular header made by Rod's Headers that features stainless construction throughout and robust flanges for optimum reliability and performance. But for our test, we stuck with the E3 casting that our car came equipped with for consistency and to measure the gains that would come from just freeing up the exhaust after the turbocharger. To see what a header can do on a more modified car, read the accompanying sidebar.