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In the world of performance exhaust systems, four-inch has become the standard by which exhaust systems are compared for the Cummins B 5.9 engines. While they are those who claim large horsepower gains with the installation of a straight-through exhaust system, we have learned the tried and true formula (fuel plus air equals power) is the key to horsepower gains, and not necessarily the exhaust system. While the systems do assist in relieving turbine inlet and outlet pressures (which in turn aids the engine's ability to develop power), is the key to horsepower gains, and not necessarily the exhaust system. While the systems do assist in relieving turbine inlet and outlet pressures (which in turn aids the engine's ability to develop power), the primary mechanical benefit comes in the performance exhaust system's ability to dissipate heat. With almost 82% greater surface area over that of the stock Dodge exhaust system, exhaust gas temperatures from engines that have been "Fuel enhanced" are more likely t stay in a range that is conducive to "normal" piston life (1250 degrees when measured "turbine in")
MagnaFlow has become one of the latest entries to the four-inch performance diesel exhaust market with the introduction of their stainless steel mandrel bent system. Offering a lifetime warranty, polished muffler and five-inch tip, the system was installed on a 1998 12-valve Club Cab, manual transmission, 4x4, test truck and to witness dyno runs in verifying horsepower and torque from the new system.
Installation
Fit is one of the key elements of an aftermarket exhaust system. With little room to spare between the engine and frame on the front, and even tighter clearances over the rear axle tube and around the spare tire, bends and lengths must be precise to achieve a fit which does not require alteration of the stock components (read: removing the spare tire or bending framing members and supports).
Carefully engineered, the MagnaFlow system's mandrel bends (smooth, even bends with no evidence of tubing collapse), lengths, angles and supports required no modifications to aid the installation. With plenty of clearance to prevent annoying rattles or potential damage to the spare tire, we found the polished muffler and five-inch angular-cut, rolled-edge stainless steel tip to provide all of the necessary elements required for a "show-n-shine" winner. A pleasing but authoritative exhaust note is presented by the system, and we'll always vote a big plus for that.
Dyno Results
 Establishing an accurate base line to measure the increased or decreased value of a performance enhancement is an essential element of any testing protocol. Prior to any modification of the test truck's exhaust system we weighed in on a certified scale (your local storage company, truck stop, landfill or gravel pit) so as to provide actual weight input for the chassis dyno's computer.
With calibrated input to the dyno's computer we made the first of three (we averaged the best of three) dyno runs to establish the test truck's baseline horsepower and torque. The Red (oh please give me a ticket) Ram had previously paid a visit to Merlon Johnson's shop (949) 322-1488, so it was not a surprise when the truck's average maximum horsepower displayed 307.5 at 2,450 rpm and average maximum torque of 685.7 at 2,100 rpm (way to go Merlon).
After completing the installation of the MagnaFlow four-inch exhaust system, the test truck was strapped to the dyno's hold downs and three more runs were made. Averaging the results of the runs, the maximum horsepower showed at 309.4 and torque was 701.6, both at almost the same rpm peaks as the baseline runs. Adding the MagnaFlow system provided a net gain of approximately two horsepower and approximately 16 lb.ft. of torque.
The Cool Factor
While there are several gains to be had from four-inch exhaust systems, the two most prominent pluses are the four-inch system's ability to relieve turbine inlet and outlet pressure decreasing "turbo lag," and an increased capacity to dissipate heat. Now, that's not to say that a four-inch system doesn't add a "cool factor" to the Ram diesel. It most certainly does. Not many would argue the enhanced value of a polished five-inch tip and muffler. Polished muffler, you say. Would even see that? Are you kidding? At most of the Dieselfests we've attended there are just as many feet standing next to the truck as protruding from underneath.
The suggested retail is $1,295.77, which does not include installation.
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