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Why Cat C15 Acert Single Turbo Conversions Are So Popular

Written By, Mike McGlothlin

As federal emission standards for diesel engines became more stringent in the early 2000’s, Caterpillar transformed its C15 (and several other engines) into ACERT models. The acronym, which stood for Advanced Combustion Emissions Reduction Technology, debuted various new technologies and diesel engine upgrades that were intended to help curb nitrogen oxide (NOx) and particulate matter (PM) pollutants. Along with being equipped with intake valve actuators (IVAs), the C15 ACERTs came with a compound turbocharger arrangement. The emissions-friendly C15 ACERT was a different animal from the C-15 and C-15 bridge engines that had preceded it, and many owners quickly came to dislike the new, multi-turbo CAT engine.

Common complaints with the factory compound turbo system are turbo lag, cost of replacement, and the fact that its added complexity makes the C15 engine itself more difficult to work on. For those reasons (and others, which we’ll delve into below), loads of C15 ACERT owners have ditched the factory compounds in favor of a singlae turbo configuration. In fact, single turbo conversions are so popular that many aftermarket retailers offer complete, bolt-on kits to simplify the job. Below, we’ll expand on why so many owners perform the conversion, what’s involved in the process, and then weigh the advantages and disadvantages of a single turbo system.

Reason #1: Simplicity

First and foremost, the single turbo conversion process is a fairly big undertaking on a C15Caterpillar C15 Acert Kenworth W900L ACERT—and it’s also not cheap. You can easily spend upward of $5,000 depending on other diesel engine upgrades you make during the install. But even though it’s expensive, a single turbo conversion simplifies the engine tremendously. Not only is there one less charger to worry about failing at some point, but the reduction in intake and exhaust plumbing alone greatly reduces the chances of developing a power-robbing boost and/or drive pressure leak. Additionally, and as you can see here, a single turbo opens up a lot of working space on the passenger side of the C15 engine.


Reason #2: Cooler EGT

Improved MPG Building on the simplicity factor, C15 ACERT owners also convert to  a single turbo for cooler engine operation and an uptick in fuel economy. That’s right, Diesel Engine Pyrometer Gauge EGT with a  properly spec’d single turbo—coupled with the right engine calibration—the C15 ACERT diesel engine upgrade will often produce lower exhaust gas temperature (EGT) than the factory compound turbos do. And, because most single turbo conversions entail fueling tweaks through ECM tuning, a significant performance increase usually occurs. The higher-horsepower and cooler-running engine, left in the hands of an astute driver, is known to consume fuel at a more efficient rate than a C15 ACERT equipped with the factory turbos.


Reason #3: Cost

Even though we’ve already admitted that a single turbo conversion is expensive, cost still plays a part in why many owners follow through with the process. This is because the C15 C15 Acert Cat Engine Factory Compound Turbo Parts ACERT’s compound turbo arrangement is a pretty penny to replace—and even if you’re only replacing one turbo, it pays to consider replacing the other one (or at the very least performing a minor component rebuild) at the same time. A factory compound arrangement sourced through a CAT dealer can get costly in a hurry, not to mention the fact that you’re guaranteed to see downtime. With many single turbo C15 ACERT owners running a common (i.e. off the shelf), BorgWarner S400-based unit (more on them in a bit), even if they do have a turbo issue it can be remedied on the side of the road.

Less Stress On The Engine

With any compound turbo arrangement, boost is multiplied, along with drive pressure. At Single Turbo Swap Cat C15 Acert Diesel Engine the factory power level, these compounding pressures are fine, but sprinkle in some extra horsepower and both boost and drive go up. In the case of an aggressively-tuned C15 ACERT equipped with the OEM compounds, excessive boost and (especially) drive pressure can take a toll on the head gasket—even blow it. A properly sized single turbo is not going to produce excessive boost or drive pressure, and overall pressure is going to be lower. These lower overall pressures will make life much easier on the head gasket.

What’s Required To Perform A Single Turbo Swap

So, what does it take to bolt a single turbo on to your C15 ACERT? This comprehensive Momentum Worx Caterpillar C15 Single Turbo Conversion Kit kit from Momentum Worx should give you a good idea. First, a different exhaust manifold will be in order, as you’ll need a different flange (or foot) to match the new S430-based BorgWarner Due to its location, a different turbo downpipe is required, along with new oil lines (supply and drain) and different air cleaner piping. New charge air cooler piping will be required as well, primarily because the factory pre-cooler will be scrapped. And don’t forget the various odds and ends (intercooler boots and clamps, adapter fittings, hardware, and gaskets) you’ll need. Finally, you’ll need the right turbo.

The Preferred Turbo

The base replacement unit of choice for Cat owners converting their C15 ACERTs to a BorgWarner S430 Turbo Cat C15 Acert Diesel single turbo is an S430-based BorgWarner. Equipped with a cast 78mm compressor wheel (inducer), the standard 96mm turbine wheel (exducer) and a 1.32 A/R exhaust housing with a T6 divided turbine housing inlet flange, this fixed geometry, non-wastegated charger adequately supports C15 engines making between 425-600 hp. The robustness and affordability of this journal bearing turbo is tough to beat, and its center section can be upgraded via a 360-degree thrust bearing assembly. Larger, freer-flowing exhaust housing options of 1.45 A/R and 1.58 A/R are also available, and are often used in higher horsepower applications.

Performance Options

Speaking of higher horsepower applications, many single turbo C15 owners opt for a Air Tec Innovations 80mm CAT C15 Acert Turbo different 78mm compressor wheel material, an optimized design, a slightly bigger wheel, or all of the above. An S430-based turbo from Air Tec Innovations can be had with a titanium 78mm compressor, paired with the standard 96mm turbine wheel, your choice of a 1.32, 1.45 or 1.58 A/R exhaust housing, and supports up to 750 hp. For added durability, this turbo also makes use of a larger, CAT-specific turbine shaft and bigger journal bearings. The company’s titanium 80mm version of the same turbo (shown) can support north of 750 hp.

Does The Engine’s Compression Ratio Need To Be Lowered?

No. Converting your C15 ACERT to a single turbo doesn’t necessarily warrant lower CAT C15 Acert 625 Horsepower Diesel Engine compression pistons. In performance builds, lower compression pistons allow more fuel and air to be crammed into the cylinders while simultaneously lowering the risk of popping the head gasket. Many 550 hp and under C15 ACERT engines left the factory with 18:1 compression, and there is no need to run lower compression pistons in conjunction with a single turbo conversion, provided you’re not going to pursue a lot of additional horsepower. As a general rule of thumb with C15 ACERTs, 17:1 compression pistons are a good idea for the 600-625 hp range, and 16.5:1 or 16:1 is recommended for power levels beyond that.

Tuning: The Glue That Holds Everything Together

At the end of the day, all of these engines are electronically controlled, so the electronic PDI Tuner Caterpillar C15 Acert Big Boss Monitor Screen side of the equation is what allows you to take advantage of any mechanical changes. The make-or-break mod in any single turbo conversion boils down to one thing: tuning. The ECM has to be properly programmed in order to: 1) keep the engine happy, and 2) get optimal performance out of the single turbo setup. Unrefined ECM calibrations can lead to poor, laggy drivability, excessive heat, and low fuel efficiency. Well-refined tuning results in favorable drivability, minimal turbo lag, and can increase fuel economy. Of course, a notable horsepower increase is also often on the table with sound ECM tuning.

A Case For Keeping The Compounds

What gets lost in the single turbo debate is the fact that there is nothing wrong with the Compound Turbo System Cat C15 Acert factory compound arrangement. Yes, Cat’s C15 ACERT is laggy in stock form, but this is a problem that can easily be rectified with a revised ECM calibration. In fact, a finely tuned C15 ACERT equipped with the factory turbos will outperform a single turbo setup in virtually every measurable way (drivability, low-rpm responsiveness, midrange and top-end power, fuel economy). Simply put, your power curve is much broader with the compounds still in the mix. However, once you venture beyond what the factory turbos can support in terms of horsepower, you risk pushing them out of their map, which is both harder on the turbos and the engine. Bottom line: if you’re chasing a horsepower number, go single turbo. If you’re after optimum drivability and are OK with moderate horsepower, stick with the factory compound arrangement.


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