6.5L Turbo Diesel Fuel Injection Tech - Marine vs On-Road

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6.5L Turbo Diesel Fuel Injection Tech
Marine vs On-Road
April 2009
Is it possible for the 6.5L Turbo Diesel to produce more than 250-rwhp?

by Jim Bigley

A lot has been said in recent years about using marine fuel injection system components for an on-road 6.5L turbo diesel application. For those who may not know, connecting the word "marine" with the GM 6.5L diesel began with the development efforts at Peninsular Diesel. Specially calibrated marine fuel injectors, marine fuel injection pump calibrations and marine oriented turbochargers all came from the "boat" point of view at Peninsular. A marine 6.5L diesel must be equipped to cruise at approximately 2600-2800 RPM for extended periods of time, and make efficient power at those engine speeds. Not coincidentally, Peninsular's marine 6.5L turbo diesels produce maximum torque and deliver an efficient fuel consumption rate at that same RPM range. It's all about the torque peak... To work with the marine paradigm in engine speeds, the fuel injection system must meet the needs of the engine RPM (and of course, meet the expectations of the boat owners). Here's what we know about marine 6.5L fuel injectors and marine fuel injection pumps.

The factory Bosch on-road 6.5 fuel injector is identified as order number 0 432 217 276, and is calibrated for an opening pressure of 142.0 bar (2059-psi). The Bosch pintle nozzle as shown above is stamped with the identification number DN0SD304, which indicates this is an on-road factory 6.5TD calibration. On the other hand, the Bosch marine 6.5 fuel injector is identified as order number 0 432 217 255, and is calibrated for an opening pressure of 150.0 bar (2175-psi). Multiply the bar by 14.5 to arrive at psi. The Bosch marine pintle nozzle is stamped with the identification number DN0SD311. Anyone buying marine nozzles off eBay should verify the ID number to make sure what you're getting is, in fact, a Bosch marine pintle nozzle.

So, we now know the Bosch marine nozzles operate at a higher opening pressure (pop pressure), but what about flow rates?

The Bacharach fuel injection test and calibration machine shown above is used at U.S. Diesel Parts for all of their Stanadyne rotary DB2 fuel injection pumps. In addition, the test machine uses its own "high pressure test pipes" and "calibrating injectors" (shown in the next image), which allow for swapping-in different size orifice plates (bottom of image).

I asked Jason, their lead Stanadyne tech, about injector flow rates, and whether the marine injectors flowed more fuel than the stock on-road varieties. Jason didn't have an answer, and further indicated that injector flow rates were not listed in any of his Stanadyne or Bosch literature (which he printed out for me). The Stanadyne documentation indicated that the high-output 310-hp DB4831-5722 marine mechanical fuel injection pump was calibrated using test injector orifices of 0.6mm, where the 250-hp DB2833-4974 marine mechanical fuel injection pump and the DS4831-5521 (a 2000 model-year on-road electronic fuel injection pump) were each calibrated using 0.5mm orifice plates in the test injectors. Jason indicated that the larger orifice plates used for the 310-hp marine pump would reflect a requirement for higher flow rate injectors to achieve calibrated flow rates.

So, the marine fuel injectors have a higher opening (pop) pressure and appear to have a higher flow-rate capacity. I mentioned to Jason that these fuel injection pumps use positive displacement pumping plungers. I said that the volume for each set of plumping plungers is a fixed and finite value, and changing the opening diameter in the test injector orifice wouldn't appear to have any effect on the total volume of fuel being injected by a DB2, DB4 or DS4. Jason disagreed. He said that while it might not seem logical to assume that total fuel flow could increase, the flow rates do, in reality, increase when using marine spec injectors. He couldn't explain why, but appeared pretty certain about his opinion. I'm still not totally convinced, and wish there was more data to look at.

Being the curious sort, I asked Jason if there was a way to measure the marine & on-road injector fuel flow using the Bacharach fuel injection test machine. As it turns out, there's not. The "calibrating injectors" used in the Bacharach test machine allow for interchangeable orifices, but there's no way to substitute the test injectors for an actual fuel injector without designing and machining a set of adapters that would allow connecting the fuel injection pump to a set of on-road or marine fuel injectors.

6.5 owners have long pondered the question concerning which fuel injection pump might offer the best performance, in terms of horsepower and torque. While at USDP, I looked at 3 of the highest rated Stanadyne fuel injection pump calibrations used for the 6.2/6.5L diesel, two of them mechanical and one of them electronic - which was a civilian Stanadyne DS4-5521. Calibrated flow rates for the Stanadyne fuel injection pumps are rated in "mm³/Stroke" at specific engine RPM points. Of the Stanadyne fuel injection pump spec sheets I had access to, the following three were the most relevant.

• 6.2L Turbocharged 250-hp mechanical DB2833-4974, maximum fuel rate of 81.5mm³/Stroke @ 2000-RPM, and 68.5-73.5 @ 3600-RPM.
• 6.5L Turbocharged 310-hp mechanical DB4831-5722, maximum fuel rate of 79.0mm³/Stroke @ 2600-RPM, and 73-77 @ 3500-RPM.
• 6.5L Turbocharged 2000 model-year electronic DS4831-5521, maximum fuel rate of 89.9mm³/Stroke @ 2000-RPM, and 65.2-75.2 @ 3400-RPM.

The data for the marine DB4 mechanical pump didn't show a fuel-rate number at the 2000-RPM setting, indicating that the marine specification max fuel-rate at 2600-RPM was the more important data point. The max fueling data for all of the pumps I looked at occurred well below the max governed engine RPM. Some theorize that the thermodynamics of diesel fuel combustion require a certain length of time for the fuel to burn during the power stroke. A higher engine RPM doesn't allow for enough burn time, so the max fuel-rate is scaled back as engine RPM rises - while simultaneously advancing the injection timing to increase the burn time.

To help understand the relationship between fuel-rate, boost pressure and 6.5L diesel engine power, lets consider the original 2001 LB7 Duramax 6600. This engine was GM/EPA certified to produce 300-hp @ 3100-RPM (at the flywheel) with a fuel-rate of 91.7mm³. The turbocharger used on the LB7 Duramax delivered a maximum boost pressure of about 20-psi.


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So, to get a 6.5L diesel to perform similarly to the original LB7 6.6L Duramax, you'd need roughly the same fuel-rate, the same boost pressure and run it at the same RPM. There are other marine specification DB4 mechanical fuel injection pumps available that supposedly allow the 6.5 to produce up to 400-fwhp when using twin turbochargers, a highly efficient water/air intercooler and an entire lake for engine cooling. For a realistic HP number in a pickup truck, we'd need to scale that back by about 25% - to something approaching 300-flywheel hp (or 250-rwhp), and when using the right fuel injection pump, the right injectors, an air/air intercooler and of course the right turbocharger. A Holset HX-35 or HX-40 would be good candidates to experiment with - think in terms of an efficient 20-psi boost pressure above 3000-RPM. The factory GM turbo is simply too inefficient for 300-fwhp.

So, what's all this mean? We now know that marine-spec injectors operate at a higher opening pressure and possibly higher flow rates. This information should help those buying Bosch marine nozzles off eBay. Unless the seller is a member of The Diesel Page, you likely know more about the Bosch nozzle ID numbers and fuel injection pump specs than he does. This exercise also showed us that the electronic DS4 fuel injection pump can produce slightly higher flow rates than the 310-hp marine mechanical, but only at 2000-RPM. The marine-spec fuel injection pump pulls ahead of the electronic pump slightly at the mid to higher engine speeds where horsepower is made, but even that fuel rate falls far short of the 2001 LB7 Duramax spec fuel rate at 3100-RPM.

In short, despite the optimistic flywheel horsepower numbers listed in the Stanadyne literature, no 6.5 DS4/DB2 fuel injection pump (marine/off-road or on-road) can deliver a fuel-rate capable of producing more than about 250-rwhp on a chassis dyno using diesel fuel and boost alone in a pickup truck.

Back in about 2007 I attended a diesel dyno day here in Montana. Attending that day were quite a few Duramax, Powerstroke and Cummins trucks. Among them was a lone 6.5L turbo diesel owned by Bill Heath. Bill didn't come himself, but the guys who drove the truck to Montana were eager to put it on the dyno. That 6.5 truck was equipped with a Heath program, water/methanol injection, propane injection and nitrous oxide. Everything but the kitchen sink was thrown at the truck to make power. What did it do, you might ask? It managed to barely break the 300-rwhp figure, while sounding a lot different (scarier) than every other diesel I've ever heard on a chassis dyno - and I've witnessed thousands. I'm mentioning this here to make a point... I would challenge any 6.5 performance product retailer to demonstrate 300-rwhp on a certified chassis dyno in a 6.5L equipped pickup truck while running on diesel fuel and turbo boost pressure alone. It's not possible because of the fueling limitations inherent in the Stanadyne fuel injection pumps. I truly like the 6.5L TD, but the fueling limitations of the Stanadyne fuel injection pumps discussed here make the "500-hp" online claims seem a little silly.

TDP