Available in 16-gauge aluminized, T-304 micro shine stainless steel or t-409 stainless steel. The Rapid Flow Exhaust Systems have the lowest degree mandrel bends offering free flowing and low back pressure. This will lower exhaust temperatures by as much as 200 degrees and provide 10 - 20 hp increases dependent upon size upgrade and current horsepower output. Bully Dog recommends using a 4" exhaust system for horsepower applications less than 400 hp, while the 5" systems are recommended between 450 to 550 horsepower applications, and our new 6" systems are recommended for trucks producing more than 550 hp. click to enlarge 4" Aluminized Exhaust Systems Vehicle Applications Hp/TORQUE increase '94-'98 Ford 7.3L Power Stroke with 3" Down Pipe + 14 hp/28 lbs.-ft. '99-'03 Ford 7.3L Power Stroke + 14 hp/28 lbs.-ft. '99-'03 Ford 7.3L Power Stroke F-350/450 with Auxillary Tank + 13 hp/27 lbs.-ft. '03-'04 Ford 6.0L Power Stroke + 13 hp/27 lbs.-ft. '03-'05 Ford 6.0L Power Stroke F-350/450 with Auxillary Tank + 13 hp/27 lbs.-ft. '94-'02 Dodge Cummins + 14 hp/28 lbs.-ft. '03-'04 Dodge Cummins + 13 hp/27 lbs.-ft. '01-'04 GM Duramax LB7 + 14 hp/28 lbs.-ft. '04.5-Up GM Duramax LLY - Catback + 14 hp/28 lbs.-ft. Click Below for information on: • 4" T-409 Stainless Steel Exhaust Systems • 4" T-304 Stainless Steel Exhaust Systems • 5" Aluminized Exhaust Systems • 6" Aluminized Exhaust Systems • Dual Exhaust Systems Benefits: •Additional Horsepower •Lower Exhaust Gas Temperatures •Better Throttle Response •Full Body Sound •Minimal Degree Angles on Bends •Increased Fuel Economy, Depending on Driving Habits Testimonial: Hello there, Happy to say I have outfitted my 2002 3500 with a Bully Dog 4" exhaust stem to stern. What a great system, sounds awesome. I have had a lot of inquiries about the truck... I'm sure the questions about the great performing / sounding truck won't stop. Thank you. Signed a very happy customer. - R Campbell Penticton, BC, Canada