Rearend 9” IRS Late Model Swap from the Driveshaft Shop

The Search for Traction – Part 1

Over three previous issues—December, 2011 and January 2012—we detailed the weakness inherent in the LX/LC platform late model HEMI Mopars. Charger/300/Magnum cars and even the Challengers have axles that can’t take power adders without breaking, much less power adders and sticky tires on a race track. The center sections are a bit dicey too.

At that time, MoparMax’s Project Maulin’ Magnum street/strip car was ready to try nitrous oxide and then a supercharger. But we knew better than to throw more power at the stock rearend. So we upgraded the flimsy stock axles to a set of The Driveshaft Shop’s level 5, 1400 horsepower rated axles. The axles come with new wheel hubs and are famously stout. Charger/300/Magnum vehicles don’t come with mechanical limited slip differentials, instead the car uses the anti-lock brake computer to mimic an LSD by applying the brake to one rear wheel as needed to get both wheels spinning. It works, but it’s not perfect and one wheel burnouts aren’t good for consistency when racing. So we added an OS Giken limited slip and were very happy. The OS Giken is one hella strong and effective LSD.

We also upgraded the ring and pinion. We ditched the stock 3.06 gears and got our hands on a Richmond 3.55 gearset for our Getrag 215mm rearend. 215mm works out to 8.46 inches, which isn’t a very big ring gear for a heavy, high output car so to get every bit of reliability and strength we could we had the ring and pinion shot peened and micro polished. We bolted it all back together and then progressively turned up the wick on the engine’s power output.

We started with a 50 horsepower shot of nitrous spraying at wide open throttle. We then upgraded to a 150 hp shot running a window switch to spray only at 2,400 RPM and above. Finally we bolted on a Magnuson Supercharger and put 6-7 pounds of boost to the engine. Crank horsepower was about 600, which was both entertaining on the street and good for quarter mile ETs into the high 11s. We carefully monitored for detonation by data logging with our Diablosport Trinity on every pass and did what we could to keep everything alive. It all worked, we racked up over 400 drag strip passes and 30,000 miles on that combination.

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