Why Blueprint Turbochargers?
In recent years, “blueprinting” turbochargers has become a popular way to raise horsepower and overall efficiency of older diesel engines.
By re-sleeving and cleaning up the interior turbo housing to encourage superior airflow, instead of unnecessarily replacing engine parts, boats are now able to increase their performance while decreasing fuel consumption and staying at a consistent rpm.
More airflow makes for more complete combustion, resulting in less unburned fuel-smoke, and more power. More complete combustion can lead to better mileage as well.
Sulfur in fuel, when combined with water vapor from the combustion process, forms sulfuric acid. Similarly, when nitrogen oxides mix with water vapor, nitric acid is formed. Over time the acids, natural byproducts of the combustion process, erode the inside of the cast iron turbine housing. The turbine blades are unaffected by this because they are made of super grade non-corrosive alloys and resist high temperatures and chemicals.
As this erosion occurs, the clearance between the inside of the turbine housing and the turbine blades increases. There is a certain amount of clearance built into the housings to allow for heat expansion, and for the “floating” bearings in the turbocharger center. As the clearances increase, the turbocharger efficiency drops.
At some point, all Marine Diesel Turbocharged engines will experience this phenomenon. Experience tells us that tip to blade clearance greater than .020” will lose efficiency. As that dimension increases past .035”, the turbochargers begin to perform more poorly. The most noticeable symptoms are slow acceleration, long durations of black smoke during acceleration, higher fuel consumption and loss of horsepower at ¾ to full throttle. Most people first notice the boat being slower to plane and the loss of RPMs at full throttle settings. This slow deterioration of performance typically occurs within 1000-2000 hours or 10-12 years.
To verify that turbochargers are working correctly or not, one can perform a boost pressure check and an EGT Test. Comparing current test results to the results of the new boat’s original testing allows one to conduct a proper comparison. If no test data is available, the turbochargers can be measured with the exhaust system removed.
What's involved in “Blueprinting” a Turbocharger?
The process of blueprinting involves removing the turbocharger and disassembling it during a turbocharger overhaul. The exhaust housing is machined out to accept a CNC insert to perfectly match the turbine blades curvature and restore blade tip to housing clearances. The turbine housing is bored and readied for the new sleeve. A special material is chosen to match the heat characteristics of the cast iron turbine housing. The blueprinter can get the tolerance to meet production factory clearances and restore efficiency back to new or better.
Keep up with your maintenance and keep on boating!
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