Fleece Cheetah vs ATS Aurora VFR: Which Drop-In Turbo Is Right for Your Cummins, Duramax or Power Stroke?

Two of the best-known drop-in turbochargers in the diesel world take very different approaches to the same problem: your factory variable-geometry turbo is the weak link. Fleece's Cheetah chases airflow and a 650-700 horsepower ceiling with a signature 63mm forged wheel. ATS's Aurora VFR chases durability and factory-like manners with a staged 3000 and 4000 lineup. We stock both, across Ram, Chevy/GMC and Ford, and this is the guide we wish existed when customers call to ask which one to buy.

Both turbos share the same core promise. They bolt into the factory location, they reuse the factory intake, exhaust and intercooler plumbing, they keep the exhaust brake and cold-start functions the truck was designed around, and they are sold as brand-new units rather than rebuilt cores. Fleece's Cummins, L5P Duramax and Power Stroke Cheetahs carry CARB Executive Order numbers, and ATS builds every VFR to work with the full factory emissions system in place. So the choice is not "which one is legal" or "which one fits." The choice comes down to how much power you are building toward, how you use the truck, how much you value adjustability and warranty, and what each brand actually offers for your specific engine.

Why the factory VGT turbo is the first thing to fail on all three platforms

Every modern three-quarter and one-ton diesel uses a variable-geometry turbocharger: the Holset HE351VE and HE300VG on the 6.7L Cummins, the Garrett units on the Duramax and Power Stroke. A ring of movable vanes changes the effective size of the turbine housing, so the turbo behaves like a small, quick-spooling unit at low RPM and a larger, free-flowing unit at high RPM. It is also what gives you an exhaust brake without any extra hardware.

The weak point is the vane mechanism itself. Soot and heat cycles cause the unison ring and vanes to stick, which shows up as a sluggish exhaust brake, a lazy spool, a check-engine light for turbo actuator position, or in the worst case a truck that goes into limp mode with a trailer behind it. Add a tune that leans on the stock turbo for more boost and the factory cast compressor wheel becomes the next limit: it runs out of efficient airflow around 500 horsepower, exhaust gas temperatures climb, and drive pressure goes up faster than boost.

Both Fleece and ATS built their drop-in turbos to solve those two problems at the same time. Where they differ is in how they weighted them. Fleece weighted airflow first, then durability. ATS weighted durability first, then airflow, and gave you two sizes to choose from.

Fleece Cheetah: the 63mm FMW wheel and the roar that comes with it

Fleece Performance Engineering, out of Indiana, built its reputation on the Cheetah line, and the concept has stayed remarkably consistent for over a decade. Take the factory turbo architecture, machine a larger, stronger compressor wheel into a matched housing, upgrade the turbine side to flow more exhaust, and leave everything the truck's computer expects exactly where it was.

What FMW means and why it matters

FMW stands for Forged Milled Wheel. Instead of a cast aluminum compressor wheel like the factory part, the Cheetah's 63mm wheel starts as a forged aluminum billet and is CNC-machined to shape. Forging aligns the grain of the metal, so the wheel resists the cyclic stress of spinning past 100,000 RPM without fatiguing the way a casting can. It also lets Fleece cut thinner, more aggressive blade profiles than a mold could ever release, which is where the extra airflow comes from. Compared with the roughly 60mm cast wheel on a stock HE351VE, a 63mm inducer is about a 10 percent increase in swept area, and because the blade design is also more efficient, the real-world airflow gain is larger than the number suggests.

On the turbine side, every current Cheetah for the 6.7L Cummins, L5P Duramax and 6.7L Power Stroke uses an Inconel turbine wheel. Inconel is a nickel-chromium superalloy that holds its strength at exhaust temperatures that would soften a standard turbine wheel, which is exactly what you want in a turbo that is going to be asked to move more air, more often, at higher boost.

Ratings by platform

• Ram 6.7L Cummins, 2013-2018 and 2019-2024: supports up to 700 RWHP. Fleece's newest Cummins Cheetahs are the highest-rated drop-in turbos in this comparison.
• Ram 6.7L Cummins, 2007.5-2012 (HE351VE): the original Cheetah, also built on the 63mm FMW wheel and generally quoted in the 650-700 RWHP range.
• Chevy/GMC Duramax LML (2011-2016) and L5P (2017-2023): supports up to 650 RWHP. The L5P version reuses the factory actuator so there is no calibration step.
• Chevy/GMC Duramax LLY/LBZ/LMM (2004.5-2010): the Street Cheetah is rated at 625 RWHP with a 63mm FMW compressor and a 66mm turbine wheel.
• Ford 6.7L Power Stroke, 2015-2019: supports up to 650 RWHP.
• Ford 6.0L Power Stroke, 2004.5-2007: rated at 650 RWHP and sold with no core charge.

Two more things define the Cheetah. The first is the sound. The 63mm wheel and its housing produce a distinctive whistle on spool that Fleece leans into with the Cheetah name, and owners either love it or plan around it. The second is the warranty: a two-year limited parts warranty across the line, with a $500 core charge on the Cummins and Power Stroke units that is refunded when your factory turbo comes back.

ATS Aurora VFR: Variable Factory Replacement, in two stages

ATS Diesel Performance, out of Colorado, has built turbo kits for Cummins trucks since the Aurora 3000, 4000 and 5000 non-variable kits of the early 2000s. The VFR line applies that lineage to the factory variable-geometry architecture. VFR stands for Variable Factory Replacement, and the name tells you the philosophy: keep the factory's variable geometry, keep the factory functions, and re-engineer every part that fails.

Built around the failure points

The ATS spec sheet reads like a list of the stock turbo's complaints. The unison ring, which is the part that sticks, is machined from billet 316 stainless steel. The vane pack is Inconel. The bearing housing and turbine housing are cast from HSM, high silicon molybdenum iron, which resists the thermal cracking that plagues factory castings on trucks that tow hard. The turbine housing gets a high-temperature ceramic coating, the compressor housing is powder-coated, and on the Cummins units the actuator is brand new with updated solid-state electronics. On the 2019+ Cummins turbo ATS added dual turbine piston seals and full-floating journal bearings, and claims an exhaust brake roughly 10 percent stronger than stock.

Two stages, one architecture

• Aurora 3000 VFR (Stage 1) is the conservative, long-life replacement. On the Duramax and 2015-2019 Power Stroke it runs a 61mm billet compressor wheel; on the 2019-2024 Cummins it uses ATS's slim-hub 8x8 splitter wheel and is rated for 550 hp as a single turbo and 750 hp as the high-pressure charger in a compound kit. On the 2013-2018 Cummins ATS quotes roughly 100 hp over the factory unit as a single.
• Aurora 4000 VFR (Stage 2) steps up to a 64mm eleven-blade billet wheel on the Cummins and Duramax (63mm on the Power Stroke). On the 2019-2024 Cummins it is rated for 650 hp single and 950 hp in compounds. On the 2013-2018 Cummins ATS publishes real numbers: about 47 RWHP and 93 lb-ft on stock tuning, 150 RWHP with ATS tuning, sustained support for 550 RWHP without overloading the particulate filter, and 600 RWHP for short-term racing use.

The other ATS advantage is warranty. The 2019-2024 Cummins VFRs carry a three-year unlimited-mileage warranty on the turbo with one year on the actuator and electronics. The 2013-2018 Cummins units are listed at two years or 150,000 miles. The Duramax and Power Stroke units carry a three-year warranty as well, although ATS's own listings for the Power Stroke show the mileage cap inconsistently, so confirm the current terms when you order. Even at the low end, that is longer than the Cheetah's two-year coverage.

Where ATS has gaps

ATS does not currently offer a VFR for the LML or L5P Duramax, and it does not offer a 4000 for the 6.0L Power Stroke or for the 2004.5-2007 LLY/LBZ 61mm fitment in every configuration. If you drive a 2011-2023 GM diesel, the Cheetah is the drop-in in this comparison. On the 2007.5-2012 6.7L Cummins ATS does list the 3000 VFR and a 4000 VFR, so both brands compete there.

The numbers, side by side

Ratings are the cleanest place to start, so start with the platform where both brands publish complete numbers: the 2019-2024 Ram 6.7L Cummins.

Read that chart carefully, because it says two different things. As a single turbo, the Cheetah's 700 RWHP rating sits 50 horsepower above the Aurora 4000 and 150 above the Aurora 3000. But ATS designed the VFR to be the first half of a compound system, and if your five-year plan involves the 900 hp Aurora 4000 VFR / 6000 compound kit, buying the 4000 VFR today means you keep it when you add the big turbo later. Fleece's answer to that is its own separate compound and S400 kits, which do not reuse the Cheetah.

Compressor wheel size

A millimeter of inducer does not sound like much, but on a wheel this size it is a meaningful change in the corrected airflow the turbo can deliver before it runs out of efficiency. The Cheetah's 63mm sits right in the middle of ATS's range. What the chart cannot show is blade geometry and housing design, and this is where the two brands really diverge: Fleece's forged wheel is cut for maximum flow per millimeter, while ATS's slim-hub design trades a little peak flow for lower inertia and quicker spool. ATS's own note that the 4000's 64mm billet wheel is 25 grams lighter than the stock wheel is the tell. Both approaches work; they simply feel different on the road, and we cover that below.

Price

On the 2019-2024 Cummins, all three turbos land within $400 of each other. The Cheetah at $3,099 is $99 more than the Aurora 3000 and $301 less than the Aurora 4000, and it carries a 50 to 150 horsepower higher rating than either. On the 2015-2019 Power Stroke the Cheetah and Aurora 3000 are $34 apart. Where ATS wins clearly on price is the older Duramax and the 6.0L Power Stroke, where the Aurora 3000 undercuts the Cheetah by $300 and $524 respectively.

Price per rated horsepower

By this measure the Cheetah is the more efficient purchase on the Cummins and modern Power Stroke, at $4.43 and $4.15 per rated horsepower against $5.23 to $5.45 for the ATS units. On the 6.0L Power Stroke the two are within pennies of each other. The obvious caveat is that a rating is a maximum, not a promise. A Cheetah on a stock-fueled truck will not make 700 horsepower; it will make the truck spool more freely, run cooler exhaust temperatures, and hold boost at the top of the tach where the stock turbo fell off.

How they drive: spool, sound, exhaust brake and towing

Spool and throttle response

This is the most common question we get and the honest answer is that both turbos spool essentially like stock, because both keep the variable geometry that makes a stock turbo spool well. Below about 1,800 RPM the vanes are closed and the turbine sees a small housing regardless of what compressor wheel is bolted to the other end. The differences show up above that. The Aurora 3000's smaller 61mm wheel and lighter slim-hub design make it the snappiest of the three off idle; owners describe it as a stock turbo that never gets lazy. The Cheetah's 63mm wheel gives up a fraction of that immediacy in exchange for pulling harder from 2,200 RPM to redline, which is where a tuned truck lives when it is working. The Aurora 4000 sits between them on response and closest to the Cheetah on top-end flow.

Sound

The Cheetah whistles, loudly enough that it is part of the marketing. The VFRs sound close to stock. If you want the truck to announce itself, that is a point for Fleece. If you drive it to job sites at 6 a.m. or your spouse drives it, that is a point for ATS.

Exhaust brake

Both retain the factory exhaust brake in full. ATS goes a step further and claims its 2019+ Cummins VFR produces about 10 percent more braking than stock because of the tighter vane closure the stainless cage allows. On a truck that tows heavy in the mountains, that is a real benefit and it is unique to ATS in this comparison.

Exhaust gas temperatures and towing

Both turbos lower exhaust gas temperatures relative to a stock turbo on the same tune, because both move more air for the same fuel. The Cheetah's larger flow gives it the edge on a truck that is tuned aggressively and towing at altitude; there is simply more air available at the top of the pull. For a truck on a mild tow tune, the Aurora 3000's efficiency at moderate boost is more than enough, and the extra durability hardware matters more than the last 100 horsepower of headroom.

Head to head

Platform by platform: which one we would put on your truck

Ram 2500/3500 6.7L Cummins

This is the only platform where you get the full menu from both brands, and the decision is about your endgame. If the truck is a 500 to 700 horsepower single-turbo street and tow build, the 2019-2024 Cheetah is the highest-rated drop-in on the market, it carries a CARB EO, and it costs less than the Aurora 4000. If you are replacing a failed factory turbo on a truck that will stay under 550 horsepower and you want the strongest exhaust brake and longest warranty, the Aurora 3000 VFR is the smarter buy. If the plan says compounds in two years, buy the Aurora 4000 VFR now and add the 6000 later.

For 2013-2018 trucks the same logic holds, with ATS publishing hard dyno numbers on its 4000 (47 RWHP stock tune, 150 RWHP tuned) that make it easy to set expectations. For 2007.5-2012 HE351VE trucks, the original Cheetah remains one of the most proven drop-ins ever sold, and ATS lists both a 3000 and a 4000 for the platform.

Chevy/GMC Silverado and Sierra HD Duramax

On the 2004.5-2010 LLY, LBZ and LMM trucks, both brands compete and ATS is the value pick: the Aurora 3000 VFR at $2,304.99 is nearly $300 under the Street Cheetah, while the Aurora 4000 VFR gives you a bigger 64mm wheel for about $100 more than Fleece. If you are building an LBZ toward 600 horsepower, the Cheetah's 625 RWHP rating and 66mm turbine make it the performance choice. If you are keeping an LMM tow rig alive for another 150,000 miles, buy the ATS.

On the LML (2011-2016) and L5P (2017-2023), the decision is made for you. The LML Cheetah and L5P Cheetah are the drop-ins here, both rated at 650 RWHP, and the L5P unit is CARB compliant, reuses the factory actuator and ships with no core charge at $2,399, which makes it the least expensive Cheetah for a late-model truck.

Ford F-250/F-350 Power Stroke

On the 2015-2019 6.7L, the Cheetah at $2,699 and the Aurora 3000 VFR at $2,664.99 are priced within $34 of each other, so price is not the deciding factor. The Cheetah publishes a 650 RWHP rating; ATS does not publish a rating for the Power Stroke units but does publish a three-year warranty and the same Inconel vane pack and HSM casting story. Our read: a 2015-2019 truck that is tuned and driven hard goes Cheetah; a stock or lightly tuned tow truck replacing a tired factory turbo goes Aurora 3000; and the Aurora 4000 VFR with its 63mm wheel is the middle ground for owners who want ATS durability with Cheetah-level airflow. For 2011-2014 trucks ATS offers the Aurora 3000 VFR.

On the 2004.5-2007 6.0L, both are excellent and inexpensive relative to the rest of the market. The 6.0L Cheetah is rated at 650 RWHP, is built with genuine Garrett internals and upgraded 360-degree thrust bearings, and has no core charge at $1,979. The Aurora 3000 VFR for the 6.0L is rated at 500 horsepower with a 64mm inducer and comes in at $1,454.99, the least expensive turbo in this entire comparison.

Every Cheetah and Aurora VFR we carry

These are the drop-in turbochargers from both brands currently listed at Alligator Performance, organized by platform. Prices are at the time of publishing and exclude any core charge. Compound kits are listed separately at the bottom for Cummins owners planning ahead.

Ram Cummins

Chevy/GMC Duramax

Ford Power Stroke

ATS compound kits that build on the VFR (Cummins)

What to budget beyond the turbo

Neither turbo needs tuning to run, and both are sold as complete units with gaskets. That said, the truck will only make the power the turbo is rated for if the rest of the system keeps up, and a few line items belong in the same cart:

• Tuning. Both brands are clear that their ratings assume aftermarket tuning. A 63mm or 64mm turbo on stock calibration will feel crisper and run cooler, but the big gains come with a tune that uses the extra airflow.
• Fuel. On a 6.7L Cummins or LML Duramax pushing past 550 horsepower, the injection pump and injectors become the limit before the turbo does. If a CP3 conversion or larger injectors are already in the plan, buy the turbo with the headroom to match, which is the strongest argument for the Cheetah on those trucks.
• Feed and drain lines. Our Cummins turbo listings offer an oil feed and drain line add-on. If your factory lines have 150,000 miles on them, replace them while the turbo is out.
• Intercooler pipes. On the 2011-2019 Power Stroke, factory plastic intercooler pipes are a known failure point at higher boost. Our Ford turbo listings include a hot- and cold-side pipe add-on for that reason.
• Core return. Fleece charges a $500 refundable core on the Cummins and 2015-2019 Power Stroke Cheetahs; ATS charges a core on the Duramax VFRs. Send the old turbo back promptly and the net price drops accordingly.

Frequently asked questions

Ready to replace the weakest link on your truck?

Learn more

• Why Every LML Duramax Owner Should Consider a CP3 Conversion
• Does a Diesel Tune Really Make a Difference?
• Full Force Diesel 6.0 Power Stroke Injectors: Buyer's Guide
• Aisin vs 68RFE: Which Transmission Should You Build Behind Your 6.7L Cummins?