Flowmaster Case Study: The Right Exhaust System for Your Car Makes All the Difference


With some car enthusiasts, exhaust systems seem like an easy to select product – no big deal. Just find some adequate tubing, some mufflers and go. What could go wrong, right?  … Wrong!

We recently received this story about an exhaust system gone wrong. While significant money was spent creating the magnificent drive train, the exhaust was so badly designed as to cause Kevin Crocie of Colvin Automotive to wonder if the engine was damaged. After all, to have the World Products 427cid, 495hp engine only generate 258 horsepower at the rear tires, something had to be really wrong.

As Crocie ultimately determined, the exhaust system was the culprit – and was easily corrected through proper fitment. Documented here by one of Flowmaster’s technical experts, Jeff Thomas, who recently discussed the scenario with Crocie, the correction was miraculous – and cemented the fact that you can select the wrong exhaust products for your vehicle with disastrous results. This worst case scenario is a perfect example of – exhaust design gone wrong!

Colvin Automotive, an advanced auto repair and restoration facility in Austin, Texas, was chosen by the owner of this beautiful 1968 Mustang to diagnose some serious performance and drivability issues. The highly modified Mustang was equipped with a World Products 427 Windsor engine rated at 495 flywheel horsepower. After running the car on Colvin’s in-house Dyno Jet chassis dynamometer, power peaked at 258.1 RWHP (at only 3700 RPM) and 331.7 ft-lbs of torque, Worst of all, the engine exhibited what appeared to be some serious internal problems.

Kevin Crocie, Colvin’s expert engine man, said after the first dyno pull, “From the lack of power and mechanical noises coming from it, I thought the engine had been severely damaged”. Fearing the worst, preparations were made to remove the engine and tear it down for inspection. As the exhaust system was removed from the car, Crocie noted the small diameter (2.5-inch) tubing and the small round, glasspack style mufflers that were used. On a hunch, he returned the Mustang to the dyno and ran the car with open headers. This resulted in a much smoother sounding engine and a peak of 398.5 RWHP at 5700 RPM – 140 more HP – Torque increased to 385.9 ft-lbs at 4900 RPM.

At this point, Crocie contacted us at Flowmaster, having had previous successful experiences with our products. We delivered two polished 70 Series Big Block II stainless steel mufflers – PN# 53074 (as requested to match the upcoming show-quality exhaust – no internal design differences from standard products), leaving the Colvin Automotive folks to fabricate the rest of the full 3.00-inch diameter mandrel-bent dual exhaust system for the car. The headers already in place, as well as the engine, remained untouched, except for tuning once the exhaust was installed.

Upon strapping the Mustang back onto the Dyno Jet, power was found to peak at 399.0 RWHP, again at 5700 RPM (more horsepower than open exhaust), while peak torque was raised by 33.4 ft-lbs- to 419.3 ft-lbs- over the open-header run. From the initial dyno run, torque was increased by 87.6 ft-lbs!

With the Mustang now running at its full potential, Colvin Automotive has reaffirmed their belief in the performance gain achieved with Flowmaster products. You can understand the car owner’s appreciation for the major performance gains noted and he loves the famous Flowmaster sound. His fears of the car becoming ‘too loud’ were put to rest by using the Flowmaster 70 Series Big Block II mufflers, which keep the overall sound level very well controlled for enjoyable top-down driving in this one-of-a-kind Mustang.