SoCal Diesel's 427ci stroker kit comes in three different bore sizes: standard (4.055-inch diameter pistons), 0.020-inch overbore (4.075-inch diameter pistons), and 0.040-inch overbore (4.095-inch diameter pistons). If you do the math, the standard-bore 427ci stroker kit actually makes the Duramax more of a 428ci engine. Of course, that is a Ford engine size and doesn't work in the marketing world, so the number was rounded down to 427 ci. At 428 ci, the stroker kit would put out an additional 48 hp and 90 lb-ft of torque, for a total of 798 hp and 1,490 lb-ft.
Now let's take into consideration that, if you're spending the cubic dollars anyway, you may as well go for the 0.040-inch overbore pistons, and increase the engine size to 437 ci. At 437 ci, the engine could put down an extra 65 hp and 122 lb-ft of torque over the 6.6L's numbers--giving your Duramax the potential output of 815 hp and 1,522 lb-ft of torque. It could be argued that the increase in piston speed and the change in bore-to-stroke ratio may change the characteristics of the Duramax, therefore our power-per-cubic-inch equation may not be an accurate way to predict the real-world power gains. Keep in mind there are other gains to be had from a stroker kit, especially if you need to rebuild your Duramax anyway. The stock crank, rods, and pistons weigh 453.6 grams more than SoCal Diesel's stroker kit. Plus, the additional stroke should amplify the Duramax's torque.
What About Durability?
It all depends on how you use your equipment. Truthfully, anything that makes more power requires more attention. This is true with any performance upgrade. SoCal Diesel's 427ci stroker kit was developed and put in service on two test trucks. The original two test trucks used to R&D the kits are still in service as this is written.
What's It Cost?
At $11,800 the SoCal Diesel stroker kit is not for the faint of heart. The initial cost may seem excessive, but it comes with more than just a crank, rods, and pistons.
What does the kit include?
Every kit is tailored for the individual needs of the customer and is equipped with a 4130 billet steel crank, Crower billet connecting rods, a set of custom pistons, a high-quality ring set, coated race bearings, billet-steel harmonic dampener, an SFI-approved steel flywheel, new crank accessory gears, and a crank reluctor wheel. There are quite a few options that help adapt this kit to an individual's needs, like billet main bearing caps, valvetrain kits, custom CNC-ported cylinder heads, and a billet oil pump. Follow along as we photograph a 7.1L Duramax short-block buildup. DP
 A new timing gear comes installed...  A new timing gear comes installed on the stroker crankshaft from the factory. SoCal Diesel has found that it's critical to get the timing gear in the correct position for proper cam-to-crank-gear alignment. |  The Duramax block didn't require...  The Duramax block didn't require any machining to clear the new 0.250-inch-longer stroke crank. Thanks to the Duramax's high camshaft location, there weren't any camshaft clearance issues either, regardless of how big a camshaft we chose. |  The Clevite H-Series bearings...  The Clevite H-Series bearings don't use flash plating to manage contamination, so cleaning the engine thoroughly (as well as having a clean engine assembly room) was essential. A light scuff on the rear bearing (arrow) removed just enough material to provide the desired oil clearance. |