What's a high-performance...
What's a high-performance exhaust system really worth on a stock 440 car? We wondered, so we brought our Charger over to Westech to run some numbers.
We always considered the factory exhaust system fitted to Mopar musclecars as good. As factory systems of the era go, the OE Mopar exhaust was generally the best. Mopar iron manifolds were typically much better than the competition's, and the generous headpipes led to relatively quiet but free-breathing mufflers. For a while, the factory Mopar mufflers were among the most copied in the aftermarket, with many manufacturers marketing their version of the "Hemi" muffler. But as good as the factory system is, we were interested in evaluating how it performs against a modern aftermarket performance system.
Our testbed was a restored '71 Charger R/T sporting a 440 Magnum engine. Although the car had received some minor bolt-on mods in the past, we returned it to bone-stock condition for the evaluation. We wanted the baseline engine combination to be totally stock to match the totally stock exhaust system fitted to the car. From this base we would begin a series of modifications to the basic package and evaluate the performance increases step-by-step on the chassis dyno. Our first mod would be to upgrade the exhaust system with a set of headers and a free-breathing set of duals from MagnaFlow.
Although the Charger engine...
Although the Charger engine had previously been modified with some minor bolt-ons, we returned it to pure-stock form for our testing purposes. Output measured at the rear wheels stood at 252 hp.
We contacted Hooker for its PN 5903 metallic-ceramic coated Competition headers to replace the factory manifolds. Hooker markets two series of headers-the Competition and Super Competition lines. The Super Comps are made for lighter weight and closely matched primary tube lengths, and come with a higher price tag. For a street application, the Comp header's weight penalty is a worthwhile trade for the heavier-tube construction. The PN 5903 header features 1 7/8-inch primary tubes and 3-inch collectors. That's more than enough header to handle a big-block Mopar in the mid-500hp range, but not so large that low-end response and fit are compromised. For the exhaust system, we handed the car to the exhaust experts at MagnaFlow.
For our dyno evaluation, we took the Charger to the chassis dyno facility at Westech Performance Group to get our baseline numbers. The stock 440 delivered 252.0 hp at 4,200 rpm at the rear wheels, while torque came in at 365.3 lb-ft at 3,200 rpm. The numbers were in the range we are used to seeing for a stock 440.
We pulled the car off the rollers and directly onto the lift to remove the stock exhaust system. The Hooker headers went in with little trouble and no modifications or tube dimpling. The most difficult part of the header installation was removing the stock exhaust-manifold mounting studs, which can be stubborn. The tubes cleared the power steering and tucked nicely in the chassis. We were pleased with the fit. With the headers bolted in, we temporarily mounted a set of header-mount glasspacks for the drive to MagnaFlow's facilities.
MagnaFlow manufactures universal exhaust-system components as well as partial and complete systems for specific applications. The company does not market a prefabricated system for early Mopar applications, but it works with hundreds of authorized installation centers across the country which carry the MagnaFlow line of exhaust products. We brought the Charger to MagnaFlow's main tech center, where products and installations are prototyped, installed, and tested. Although our system was installed at the tech center, similar systems are routinely custom-fabricated through their many authorized dealers. We basically gave the crew at MagnaFlow full discretion to build a system to fit our requirements.
With the baseline results...
With the baseline results in, we rolled the Charger onto the lift and conned Westech's Rick Stoner into demonstrating the usefulness of his plasma cutter by removing the stock exhaust system.
MagnaFlow fabricated the pipes...
MagnaFlow fabricated the pipes from 2 1/2-inch mandrel-bent stainless exhaust tubing. The mandrel-bent tubing has more cross-section to flow better than typical compression-bent tubing. MagnaFlow offers kits made of mandrel-bent tube sections for fabrication purposes. No crossover was used.
Step one was to pull the factory...
Step one was to pull the factory iron HP exhaust manifolds that were to be replaced with a set of Hooker 1 7/8-inch headers. We were confident the headers would beef-up output even with the otherwise-stock engine.