With so many drop-in turbo upgrades to choose from it can be hard to make sure you're getting exactly what you want, and need, out of a drop-in turbo upgrade for your '04.5-'16 Duramax. Could your stock LLY, LBZ, LMM, or LML turbo be enough to crank out the power you're looking for if you really turned it up? Do aftermarket replacements really live up to their claims? Today we'll take an in-depth look at what you can expect out of varying levels of drop-in turbo upgrades for your 6.6L Duramax and compare them to what the your stock charger can provide. Below is the data from our in-depth engine dyno testing of a Stock VVT/LML turbo, Stealth STR, Stealth Mach 1, and Stealth Mach 2 turbo. All tests were conducted on a built LBZ engine connected to our Dyno-mite water brake engine dyno. This empirical data was gathered under real-world circumstances, with a serious effort made to control as many variables as possible for consistency. Installation, instrumentation, and operation of this engine through a gauntlet of tests that took several weeks.
Turbo and Test Descriptions
Dyno Engine: The platform that we will be using for this test is a 2007 6.6L LBZ Duramax that received the following upgrades before testing:
• Custom tuning
• S&B Cold Air Intake
• 100% over injectors
• 10mm CP3 pump
• Head studs
• Alternate firing order cam
• Upgraded pistons
• Upgraded crank shaft
• Upgraded connecting rods
These upgrades were necessary to be able to handle the power levels that we pushed this engine to during the testing of all 4 of these turbos.
Testing: We performed three tests to gauge the overall performance of each turbo in comparison to each other. Obviously the bigger the turbo, the more top end power. But what about all the other factors that go into creating that power like drive pressure, EGTs, air/fuel ratio, etc? What about in towing conditions and all-around drive-ability? The first test that we will present is the "Max Power" test which is your traditional dyno and power test. This test will provide a general comparison in terms of the difference in power that these different turbo options can produce. The second test presents spool up data and will give a good visualization of the difference in drivability and turbo lag that each turbo can provide. Finally our "Tow Test" is the ultimate data provider, providing insights on key data points including EGT's, drive pressure, air/fuel ratio Ect...
The Turbos:
- OEM LBZ- A bone stock 2004.5-2016 Duramax turbo charger. Coupled with custom tuning and stout engine build, this allowed us to push this turbo to its practical limits, a significant power increase over stock but still left a lot on the table.
- Calibrated Power LML/VVT STR- This turbo is designed as a performance-oriented direct drop-in replacement for the stock unit, utilizing a light weight billet compressor wheel and proprietary 10-blade turbine. This turbo provides lightning fast spool up and immediate throttle response.
- Calibrated Power LML/VVT Mach 1- When the a stock sized turbo just won't cut it, this turbo is designed for higher power levels while maintaining fast spool up, throttle response, and towing performance. This turbo uses a 64mm custom billet compressor wheel paired with an oversized compressor wheel.
- Calibrated Power LML/VVT Mach 2-- When maximum power is desired, the 67 mm Mach 2 is a great option. Dyno proven to support up to 800 rwhp while maintaining good low end power and quick spool up. This turbo features a turbine wheel 10% larger than stock allowing for increased airflow and lower EGTs.
1. Max Power Test
Max Power Test Background: This is a classic dyno test that everyone is used to seeing - we load the engine down as the RPM sweeps from low to high over the course of 7 seconds or so and and plot out how much power it can make throughout the RPM range.
The Stock LBZ Duramax was originally advertised to make 360 horsepower and 650 lb-ft of torque. With tuning and a fuel system on our engine, the stock turbo was able to move enough air to make 536 HP at 2800 RPM, and max torque of 1260 lb-ft at 1600 RPM, all while still maintaining a clean lambda limit of 1.15. Very impressive gains, but this power level is pushing the stock turbo to its absolute limit.
When we swapped the stock turbo out for the Stealth STR we were able to move enough additional air to gain almost 80 hp and 87 lb-ft of toque, pushing the peak numbers to 615 hp and 1347lb-ft of torque. The STR not only out-performed the stock unit in peak horsepower, but also carried 60 or more additional HP throughout a majority of the RPM range.
With a Stealth (64) Mach 1 in the place of the stock turbo power numbers were brought up considerably to 671hp at 3000 rpm. Over all we were able to pick up an additional +136 HP and +103 Ft/Lbs of torque over the stock turbo by swapping the Mach 1 into its place. The Mach 1 also pushed peak power up to 3000 RPM, and again showed more power throughout the entire RPM range.
The Stealth Mach 2 (67) increased peak power all the way up to 743hp at 3000 rpm. Resulting in a +200 HP and +135 Ft-Lbs of torque gain over all! The Stealth Mach 2 truly stands out on top if peak power is what you're after.
2. Spool- Up Test
Spool-up test background:
The spool up test is designed to test off-the line performance of each turbo. How quickly will a truck equipped with each turbo come to life? This test is a measurement of the time it takes for each turbo to go from moving enough air for 30 hp to moving enough air for 250hp at a fixed RPM. As a general rule-of thumb, the smaller the charger the faster it will spool up. The spool up test is conducted at 1500 RPM and 1700 RPM to give multiple points of comparison.
The engine dyno is set to keep the engine at a set maximum RPM. The more the accelerator pedal is depressed, the more HP the engine puts out at that RPM. Once the engine is holding steadily at the RPM and horsepower set point, the pedal is swiftly applied to 100%, and lifted after 250 HP. This process is repeated over a dozen times. The time it takes to get from 30-250 HP is grabbed from the data log and recorded, then averaged together for comparison between turbos.
Spool-up test results:
At 1500 RPM the stock turbo spooled up to 250hp in and average of 3.32 seconds, and at 1700 rpm in 2.78 seconds. The STR on the other hand spooled the fastest by far. Spooling up an impressive 10% quicker than stock at 1500 RPM, in just 2.99 seconds, and an incredible 20% faster than stock at 1700 RPM.
The Mach 1 64mm turbo was slower than the STR, but was still able to spool 7.5% faster than stock, even though it has a notably larger rotating assembly. The Mach 2 also outperformed stock in the 1700 RPM test. All around very impressive for a much larger than stock turbo!
The spool-up test is one category where the Mach 2 67mm doesn't shine its brightest, since it is such a large turbo. It was unable to complete the test at 1500 RPM. However, at 1700 RPM the 67 was able to spool slightly faster than stock at the same RPM, which is very impressive for a charger this size.
What does this all mean? Essentially this test shows the ability of each turbo to build low end horsepower. Essential for things like frequent heavy towing, stop and go drivability, and off the line performance. While the Mach 2 (67) is clearly not the best for this it is still reasonable for use in some daily driving scenarios. If you are sled pulling or racing, the 67 is a great choice just keep the RPM up! The Mach 1 (64) shines as a perfect medium ground for both building low end power and having access to a solid amount of top end power over all. However, if you're looking for peak off tine line performance and don't need much more power than the stock turbo can provide the STR reigns supreme.
3. Tow Test
Tow Test Background:
The "Tow Test" is the ultimate torture test for both turbo and engine, providing us with a slew of data. This test is performed by holding the engine at a steady RPM and HP level for several seconds to capture the data that we are looking for. We repeat this test dozens of times starting at 100 HP and increasing HP increments by 50 horsepower each time for each RPM level.
We can very the HP level at each RPM window by applying more or less load to the engine. This is why you will see the data presented at varying levels of power at the same RPM and varying RPM's at the same HP level. This test allows for a great overall comparison throughout the operating range of each engine/turbo configuration along with allowing us to compare different towing scenarios in a very controlled and repeatable environment.
3a. Actual Horsepower:
By setting a maximum RPM limit on our engine dyno the water brake will self adjust the load put on the engine to hold it at a desired RPM. This allows us to create an RPM "wall". With steady control of the accelerator pedal, we were able to get close, but not perfect to the target horsepower for each cell. This chart shows the actual values that were achieved, and lays out the framework for how the rest of the tow-test data will be presented. As we get into the larger turbos, we capped the test at 600 hp because sustained horsepower above those levels is unrealistic for towing scenarios.
3b. Intro to Lambda:
The lambda charts can show how clean (or smokey) the truck is able to run and how efficiently it is able to burn fuel at any given horsepower and RPM. Lambda refers to the air: fuel ratio during combustion which, in this test, is measured by a wideband O2 sensor in the downpipe. Lambda of 1.0 equals combustion of 14.6 AFR, 1.1 =16.06 AFR, 1.2 =17.52 AFR etc. If fuel is mixed perfectly with air, 14.6:1 combustion results in clean diesel combustion. Unfortunately perfect mixing is not a reality in this engine (by a long shot) so in order to run clean, we are looking for a Lambda value closer 1.15 ( 16.79AFR).
The ability the engine has to maintain a Lambda of 1.15 or higher is a great indicator of the engine's overall happiness in operation. Small differences in lambda (.05) have significant impact on smoke output, EGTs, and of course, reliability. The turbo has the largest impact on AFR at any HP/RPM because it controls the amount of fresh airflow coming into the engine. The highest lambda value that our O2 sensor is able to read is 1.45, so assume any value of 1.45 is at least that lean- well within the comfortable operating range of the engine.
3c. Trends in Lambda:
The darkest green cells (lower numbers) represent lambda levels low enough to cause smokiness at that RPM/Load. Factory engineers typically maintain rich lambda limits of 1.10-1.15 at peak power production to keep particulate (black smoke) production low and keep emissions control systems happy. Throughout most of the chart, you see very little change in lambda, because of the limits of our sensor and because the stock and aftermarket turbos are able to supply plenty of air to keep the engine happy at those RPM and horsepower levels.
The trends in this range (2250-3250 rpm, 100-400hp) are fairly consistent between all these turbos throughout all of the data. As the horsepower demand increases, you can see that where the stock turbo begins to run out of air- a shown by a medium green band of data where lambda drops to around the 1.15 mark. At those same power levels, the STR still has capacity to provide air so the lambda reading is more lean. For the 64 and 67, this darker green band where lambda drops off is pushed to higher and higher power levels, because the larger turbos are able to provide more air.
3d. Intro to EGTs:
Exhaust gas Temperature is a quick indicator of the safe operating range of the engine. Generally, 1350-1500°F is considered safe in the long term as long as coolant/oil temps are also maintaining a reasonable temperature. In a performance application it’s normal to see EGT's move to 1600°F and beyond for short intervals. The main concern in these performance applications is melting your turbine or burning up oil seals. This begins to happen when EGT's exceed 1500°F continuously and heat dissipation through the turbine shaft and oil cooling cannot keep up.
3e. Trends in EGTs:
Exhaust gas temperatures were measured with a thermocouple probe inserted into the stream of gasses in the exhaust manifold. This data set is subject to a lot of variables, but most importantly it shows a trend in the overall behavior of each turbo. These tests were all done with the engine at full operating temperature, generally running tests in order from top to bottom, left to right. As the engine was working harder in the higher-horsepower cells, we had to interrupt the tests and let the engine idle to cool down. Keep in mind each cell represents several seconds at that horsepower level- with a longer sustained pull at that level the temperature would climb.
In the same areas where the Lambda started to drop, higher EGTs are recorded . Generally, more air and leaner combustion results in lower EGT's. So where the stock turbo starts to run out of air and EGTs start to rise, the STR is able to keep temps down to safer levels. Then where the STR starts to show higher EGTs, the 64 is able to provide even more air to keep things cooler and so on. Almost every cell that shows 1500+ degree EGTs is a cell where the engine and turbo was giving it everything it could at 100% pedal position- the diesel equivalent to "wide open throttle".
3f. Intro to MAF:
Mass air flow (MAF) is a direct indicator of how much clean horsepower an engine can make. Fuel is important too, but as we saw with lambda and EGTs, if the air isn’t there to support the fuel then we create undesirable operating conditions. While boost measurements are affected by temperature, altitude, and other atmospheric conditions. A mass air flow number remains a true measure of air flow into the engine regardless of atmospheric conditions. MAF data was logged from the engine computer via the OBDII port.
3g. Trends in MAF:
Looking at the middle of each chart for MAF, you will see very similar numbers for each RPM/HP level. This is exactly what we would expect- MAF is a direct indicator of how much horsepower potential an engine has. At higher HP levels, you can see the stock turbo MAF values falling off compared to the STR- that is because the stock turbo is running out of capacity. Where the STR's air flow starts to drop off, the 64 and 67 are able to hit almost 650 g/s peak at the 600 hp mark.
3h. Intro to Boost:
Although boost pressure is relatively unimportant since this engine is equipped with a mass airflow sensor as discussed above, it still provides interesting data and is a metric that most truck owners are more familiar with. Our aftermarket turbos are capable of creating boost far beyond what the stock sensor is able to read, so boost in this test was sampled using an analog sensor located on the intake near the factory sensor.
3i. Trends in Boost:
Given these tests were run with very similar ambient air conditions, the boost numbers make it clear to see how the STR, 64, and 67 are able to push out more air than the stock units. To increase mass air flow with a fixed flow rate (CFM) dictated by engine RPM, like we had discussed earlier, Boost must increase. Notice how at the same HP levels, boost is higher at lower RPMs. Notice how the larger turbos are able to carry the highest 42 PSI boost value out into the higher RPM ranges. 
3j. Intro to Drive to Boost Ratios:
Drive pressure, back pressure, or exhaust manifold pressure- whatever you call it, it is an important metric to observe in relation to boost pressure. A significant imbalance in drive and boost pressures can create an uneven thrust load on the turbo bearings which can cause premature failure. Too much drive pressure limits engine performance, restricting air flow through the entire system. A simple way to look at this data for comparison is by creating a ratio of drive pressure divided by boost pressure. Values close to 1.0 are the most ideal. These turbos, equipped with variable vane technology, allows superior regulation of drive to boost ratios compared to a fixed-geometry turbo. Drive pressure was measured with a pressure sensor connected to a copper coil plumbed into the exhaust manifold right before the turbine inlet of the turbo. The copper allows the exhaust gases to cool down to protect the sensor. Below are charts for drive pressure and calculated drive to boost ratios.
3k. Trends in Drive to Boost Ratios:
In the low horsepower and mid rpm range cells, the drive to boost ratios are the best, right around 1.0. This area is the most efficient area to operate the engine. In these tests, the stock turbo had the highest drive:boost ratios. The STR was able to outperform stock, with lower drive to boost ratios in similar RPM/HP ranges and lower drive:boost overall. As we step up in turbo size, D:B ratios further improve with lower values. However, with the bigger turbos the overall drive pressure increases also, because more drive pressure is needed to create all the boost that these larger turbos put out.
3. Conclusion
Regardless of what you plan to do with your VVT/LML Duramax, Calibrated Power has a high-performance aftermarket turbo to fit your needs. The Stealth STR is an excellent option to get a little more power with great benefits like better airflow, faster spool up, and lower EGTs. The 64 is an excellent option for those who need more power than what the STR can provide while still maintaining lightning fast low end responsiveness. The 67 is a great choice for those chasing all out horsepower at safe EGT levels and all around great performance.
For more information on the turbos mentioned in this article please click the product links below:
Stealth Mach 1 For VVT and LML
Stealth Mach 2 For VVT and LML
If you're interested in learning more about the Stealth line of turbos for your 2004.5-2016 6.6L Duramax click here to visit Calibrated Power's website or give us a call at (815)-568-7920 Monday-Firday 9am-5pm (CST) and we would be happy to provide you with any information about this turbo that we can. 
Don't Forget To Check Out Our Other Articles On 6.6L Duramax Turbo Upgrades!
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Breaking Down the Stealth Turbo Line: STR, Mach 1, and Mach 2 – Which One Is Right for You?
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Stock Duramax Turbo Specs and Information
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64MM Vs. 67MM Turbo: 3 Things To Consider Before Making Your Purchase
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High Flow Vanes (HFVs) For Variable Geometry Turbos and Why You Need Them
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High EGTs? Bad MPGs? Excessive Smoke?
