Diesel Power
Mobile Icon BtnMobile Icon Btn RO
Newsletter

7.1L Duramax Stroker Buildup - It's A Diesel!

There's No Replacement For Displacement

Photography by Gary Blount

In 1966 General Motors took its famous 396ci gas-burning big-block and increased its bore to 4.25 inches. With that one simple machining process, GM gave birth to the famous 427ci Rat motor, and Chevy carved its notch into American muscle car history forever.

Ever since the 6.6L Duramax became a viable performance engine, it was only a matter of time before some horsepower junky took the 402ci diesel, ripped out its guts, and stuffed it full of forged, billet, and coated power parts in search of more cubic inches--and Guy Tripp of SoCal Diesel is just that junky.

While working on his mechanical engineering degree in college, Tripp spent his spare time building and tuning performance engines. His expertise led him to a position at Air Flow Research (AFR) where he spearheaded the task of integrating CNC machines to sculpt AFR's raw casting into performance cylinder heads. With all that experience under his belt, Tripp is not only a power junky, he's fully capable of engineering and manufacturing performance engine parts. After he purchased a Duramax in 2003, his addiction was soon directed toward GM's diesel platform.

Tripp opened the doors of SoCal Diesel three years after his Duramax purchase. Till now, SoCal Diesel has been known for its five-axis CNC-ported Duramax cylinder heads, but that may change soon. New to the market is SoCal Diesel's 427ci Duramax stroker kit that increases the size of a Duramax engine from 6.6L to 7.1L (427ci) by fitting the engine with a -inch- longer stroke. That's right, the big-block 427 is back. Only now, it's a diesel!

How Much Power Can The 7.1L Stroker Kit Add?
The only answer we can supply is a percentage increase as it relates to the increase in displacement. For example, if we agree that a 6.6L Duramax can be tuned to make 750 hp and 1,400 lb-ft of torque, then by dividing the horsepower and torque output by the engine size (402 ci), we get how much power per cubic inch the Duramax makes. Then, if we multiply that number by the number of cubic inches available from the stroker kit, we can estimate the power gain. So if a 6.6L (402ci) Duramax can make 750 hp and 1,400 lb-ft of torque, we'll divide 750 hp and 1,400 lb-ft of torque by 402ci to get 1.865672 hp and 3.482587 lb-ft per cubic inch.

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

SOURCES
ARP
531 Spectrum Circle
Oxnard
CA  93030
805-278-7223
SoCal Diesel
27833 Ave Hopkins Suite #6
Valencia
CA  91355
socaldiesel.com
  • «
  • |
  • 1
  • |
  • 2
  • |
  • 3
  • |
  • 4
  • |
  • View Full Article
Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!
0 comments
Diesel Power