7.1L Duramax Stroker Buildup - Duramax Diesel Engine

7 1L Duramax Stroker Buildup Duramax Engine

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.

If your local machine shop hasn't worked on a Duramax, you might want to contact SoCal Diesel to find a shop in your area that has. SoCal Diesel offers torque plates for the Duramax engine to ensure the cylinder bores are true during the bore and honing process. Here you can see the 300-grit stone finish required to seal the cylinders with the ductile molly ring set that comes with the SoCal 427ci (7.1L) stroker kit.
If your local machine shop hasn't worked on a Duramax, you might want to contact SoCal Die
A little lube was used on the thrust bearings to keep them in place while the stroker crank was installed. SoCal Diesel machined these Teflon main stud guards (arrow) to protect the freshly ground crank surface from harm during assembly. They worked great, and we wouldn't be surprised to see them in SoCal Diesel's catalog in the future.
A little lube was used on the thrust bearings to keep them in place while the stroker cran
The stroker crank is constructed from billet 4130 steel, and it has enhanced oiling for the main and rod bearings, knife-edged counter weights, and radiused journals for added strength.
The stroker crank is constructed from billet 4130 steel, and it has enhanced oiling for th

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 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.
A new timing gear comes installed on the stroker crankshaft from the factory. SoCal Diesel
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 Duramax block didn't require any machining to clear the new 0.250-inch-longer stroke c
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.
The Clevite H-Series bearings don't use flash plating to manage contamination, so cleaning

SoCal Diesel's optional steel main bearing caps fit tightly within the deep skirt block and provide a substantial increase in block stability. They are said to also dramatically reduce crankshaft deflection in stroker applications.
SoCal Diesel's optional steel main bearing caps fit tightly within the deep skirt block an
Setting the crankshaft thrust on the Duramax's three-piece thrust bearing was done just as we would on any other engine. A bit of pressure was applied to the crankshaft both backward and forward to verify the thrust specification.
Setting the crankshaft thrust on the Duramax's three-piece thrust bearing was done just as
Then the optional SoCal Diesel steel main bearing caps were torqued using ARP main bearing studs.
Then the optional SoCal Diesel steel main bearing caps were torqued using ARP main bearing

The SoCal stroker kit's pistons are said to be forged from a proprietary aluminum that's best suited for diesel applications. The top ring lands were coated to provide a heat-resistant surface in order to prevent ring land damage due to excessive heat. Each piston was equipped with SoCal's custom bowl design and plunged with four valve reliefs for proper compression ratio and valve clearance.
The SoCal stroker kit's pistons are said to be forged from a proprietary aluminum that's b
Each piston and Crower connecting rod assembly was pushed into its cylinder using SoCal Diesel's custom ring compressor.
Each piston and Crower connecting rod assembly was pushed into its cylinder using SoCal Di
After each piston and rod assembly was installed, the Crower connecting rod caps were bolted on, and the crank was rotated to prepare for the next piston installation. After all the caps on the connecting rods were installed, the engine was rolled over and the ARP rod bolts were torqued to 55 ft-lb of torque.
After each piston and rod assembly was installed, the Crower connecting rod caps were bolt

All the ARP fasteners were left to sit for 24 hours before they were checked for stretch, backed off, and torqued one final time for assembly.
All the ARP fasteners were left to sit for 24 hours before they were checked for stretch,
The Duramax uses piston-cooling oil jets to spray the bottom of the pistons with engine oil. In order for the oil to escape through the oil jet, it must push on a check ball and spring located at the base of each oil jet. This prevents the oil from dribbling out of the tube and forces it to shoot out of the jet under pressure.
The Duramax uses piston-cooling oil jets to spray the bottom of the pistons with engine oi
The Duramax camshaft uses a huge base circle diameter. Thankfully, the lobe lift numbers are not radically high, so installing the cam without damaging a camshaft bearing was pretty easy. SoCal Diesel offers the complete line of Comp Cams Duramax camshafts, as well as its own custom-ground profiles designed for various applications.
The Duramax camshaft uses a huge base circle diameter. Thankfully, the lobe lift numbers a

The stock Duramax cam was attached to the cam gear with only a small, round dowel, which has been known to fail in performance applications. SoCal Diesel cranks and camshafts come with large keyed locators (arrow) that provide superior holding strength to prevent any issues.
The stock Duramax cam was attached to the cam gear with only a small, round dowel, which h
The Duramax cam gear uses a reluctor wheel that works together with the camshaft position sensor to tell the ECM when to fire the injectors. This reluctor also denotes the engine's cycle. If you look closely, you can see the reluctor generates a four-count signal, and that one side is opposite the other, indicating engine cycle position.
The Duramax cam gear uses a reluctor wheel that works together with the camshaft position
Timing the Duramax camshaft and crankshaft together was done with these small dots on the timing gears.
Timing the Duramax camshaft and crankshaft together was done with these small dots on the

After torquing the cam bolt, the engine was rotated to make sure there were no clearance issues.
After torquing the cam bolt, the engine was rotated to make sure there were no clearance i
It's important to put the rear cam plug in at the right depth. If it's a few thousandths of an inch off, the gear will rub the cam retaining plate and wear the gear badly. SoCal Diesel's desired camshaft endplay is 0.004 inch.
It's important to put the rear cam plug in at the right depth. If it's a few thousandths o
With the cam gear endplay established, the timing gears can be checked for proper alignment and clearance. The desired gear-to-gear lash is plus or minus 0.001 inch for a total of 0.002 inch.
With the cam gear endplay established, the timing gears can be checked for proper alignmen