LS4 420PS NA Tune

Building a 350whp Naturally Aspirated LS4

LS4 NA Power!

An LS4 Motor

The GM LS4 is a unique member of the LS family, designed for front-wheel-drive applications in cars like the Impala SS and Pontiac Grand Prix GXP. From the factory, it produces around 303 horsepower, but when measured at the wheels, this translates to only about 240–250 whp. For enthusiasts seeking to maximize performance without resorting to forced induction, building a naturally aspirated LS4 capable of producing 350 whp is a challenging but attainable goal. Achieving this level of output requires a thoughtful combination of airflow upgrades, valvetrain improvements, and tuning to overcome the platform’s factory limitations.

The foundation of the build begins with improving how the engine breathes. A high-flow cold air intake paired with long-tube headers and a performance exhaust system dramatically improves airflow in and out of the motor. Since the LS4 is restricted by emissions-friendly factory manifolds and intake design, freeing up these bottlenecks can easily add 25–30 horsepower at the crank. While these modifications alone won’t get the engine to 350 whp, they set the stage for more substantial upgrades that will fully utilize the engine’s potential.

The most significant gains on a naturally aspirated LS4 come from a well-chosen camshaft. By moving to a more aggressive cam profile, the engine can take in more air and fuel at higher RPMs, greatly improving volumetric efficiency. Supporting this upgrade with high-performance valve springs, pushrods, and lifters ensures the engine can rev safely and reliably. Deleting the factory Displacement on Demand (DOD) system is mandatory at this stage, not only for reliability but also to prevent interference with performance tuning. With a quality cam package and supporting valvetrain upgrades, it’s realistic to add 60–80 horsepower at the crank.

Cylinder head work further enhances the setup. Ported factory heads or aftermarket options allow the engine to move significantly more air, especially in the higher RPM ranges where the camshaft is most effective. Combining ported heads with a slight bump in compression ratio through custom pistons or thinner head gaskets sharpens throttle response and increases power output. Together, these upgrades can add another 30–40 horsepower, pushing the LS4 into the 400+ crank horsepower range. When measured at the wheels, this puts the build close to the 350 whp target.

Of course, airflow upgrades mean little without proper tuning. A dyno-tuned ECU calibration is essential to optimize fuel and spark maps for premium fuel, maximize the efficiency of the upgraded cam and heads, and remove the factory torque management that restricts power delivery. With professional tuning, drivability can be maintained for street use while still extracting every bit of horsepower from the naturally aspirated setup. At this point, the LS4 can produce roughly 420 crank horsepower, which translates to about 350 whp through the 4T65E-HD transmission.

The final consideration in achieving this setup is drivetrain durability. While the LS4 itself can reliably handle 350 whp in a naturally aspirated build, the stock transmission is a weak link. Reinforcing the 4T65E-HD with upgraded clutches, a stronger input shaft, and improved cooling ensures that the additional power can be reliably delivered to the wheels. Once these supporting modifications are in place, the result is a unique, high-revving FWD LS4 that makes a genuine 350 whp without boost, a rare accomplishment that blends factory drivability with muscle-car-like performance in an unconventional platform.

Every motor and transmission has a weakness. It is very important to address your motor and transmission for weaknesses before modifying them. 

Check With Your Local Laws And Regulations Before Modifying, Swiping Motors, And Transmission..👈

Important Information Before Swapping A Motor And Transmission..👈

The Importance Of Transmission Builds..👈

How To Build A Forged Engine..👈

Unlocking NA Power!👈

1UZFE 340PS NA Tune

Building a 340hp Naturally Aspirated 1UZ-FE

1UZ-FE NA Power!

1UZ-FE Series Engines

The Toyota 1UZ-FE is a highly respected 4.0-liter V8 engine, known for its durability, smoothness, and overbuilt design. Originally developed for the Lexus LS400 luxury sedan, it was engineered to last hundreds of thousands of miles under stress while producing between 250 and 290 horsepower, depending on the year and variant. While not designed as a performance powerhouse from the factory, its strong aluminum block, forged internals in early versions, and advanced design make it an excellent platform for enthusiasts seeking more power. With the right naturally aspirated upgrades, the 1UZ can be transformed into a strong 340-horsepower street engine that maintains Toyota reliability.

The foundation of this build begins with improved airflow. The stock intake and exhaust systems are highly restrictive, prioritizing refinement over performance. By replacing the factory intake with a high-flow performance system and pairing it with long-tube headers, high-flow catalytic converters, and a cat-back exhaust, the engine can breathe far more efficiently. These bolt-ons alone typically deliver 20–30 horsepower at the crank while sharpening throttle response and adding a more aggressive exhaust note. At this stage, the engine is still daily-friendly, but the gains lay critical groundwork for later modifications.

The next major upgrade is tuning. The factory ECU is conservative, tuned for emissions compliance and quiet cruising rather than maximum output. By installing a standalone ECU or a piggyback system, fuel and ignition maps can be optimized for premium fuel. A professional dyno tune can unlock additional horsepower while also accommodating intake and exhaust modifications. Tuning is essential for extracting the full benefit of bolt-ons and ensures the engine maintains smooth drivability while safely operating with more aggressive settings. With proper calibration, this step alone can net 15–20 extra horsepower.

To reach the target of 340 horsepower, the 1UZ benefits enormously from camshaft upgrades. The stock cams are mild, built for luxury performance, but aftermarket performance cams increase lift and duration, allowing the engine to take in more air at higher RPMs. Supporting upgrades such as stiffer valve springs, titanium retainers, and upgraded pushrods ensure the valvetrain remains stable at higher revs. With cams and supporting hardware, the 1UZ wakes up considerably, adding 40–60 horsepower depending on grind and tune. This modification also shifts the powerband upward, giving the engine a sportier, more free-revving character.

Cylinder head improvements further maximize performance. Porting and polishing the heads reduce turbulence and improve volumetric efficiency, particularly in the upper RPM range. While aftermarket heads are rare for the 1UZ, carefully worked factory heads paired with performance cams can add another 15–20 horsepower, pushing the engine comfortably past 330 hp. At this point, the combined effect of bolt-ons, tuning, cams, and headwork results in a broad power curve that delivers usable street performance without sacrificing reliability or drivability.

In the end, the naturally aspirated 1UZ-FE with bolt-ons, cams, tuning, and mild headwork represents a balanced street build capable of achieving around 340 horsepower at the crank. This setup retains the legendary smoothness and durability of the engine while providing a dramatic increase in performance compared to stock. For enthusiasts, it strikes a sweet spot: enough power to transform the driving experience, without the complexity or stress of forced induction. It proves that the 1UZ, despite being born as a refined luxury engine, can be turned into a naturally aspirated powerhouse suitable for spirited street driving while maintaining Toyota’s hallmark reliability.

Every motor and transmission has a weakness. It is very important to address your motor and transmission for weaknesses before modifying them. 

Check with your local laws and regulations before modifying, swiping motors, and transmission..👈

Important Information Before Swapping A Motor And Transmission..👈

The Importance Of Transmission Builds..👈

How To Build A Forged Engine..👈

Unlocking NA Power!👈

Frankensteinmotorworks 2ARFE And 2ARFXE Swaps

2AR-FE NA Power!

A 2AR-FE

This Is Fitted For Cars For Under 3000LBS!

Do Weight Reduction! 👈

Mod The Transmission and Car!

Get Better And Approved Performance Tires!

Be The Perfect Driver! 

Selecting the Core Engine and Platform

Begin with a 2AR‑FE (factory ~205 whp) or the fuel‑economy‑tuned 2AR‑FXE (modded variant). Frankenstein Motorworks supports both, though many of the performance cams and intake parts are specific to the FE block, important if you're leaning toward more aggressive tuning. Aim to start with a running, clean engine, this ensures reliability and avoids hidden pitfalls down the line.

Valve Train and Cam Upgrades

FMW’s street cams are designed to work with stock valve springs up to ~7600 rpm, offering a noticeable bump in performance without sacrificing everyday comfort. For more track‑oriented builds, their track cams push further, but require upgraded springs and fuel system changes. These cam upgrades alone can unlock significant gains while staying manageable for street use.

Intake Enhancements: Velocity Stack Manifold

Pairing the cams with the 2AR‑FE velocity‑stack intake manifold is a game‑changer. In dyno testing on a stock motor (plus FMW cams, springs, retainers, lash caps), it produced up to 270 whp, a massive leap over stock performance. This intake dramatically boosts top‑end breathing, while still being realistic for streetability with proper tuning.

Reinforcements: Springs, Studs, and Head Hardware

To support increased RPM and performance, FMW offers 8000‑rpm valve springs, retainers, and ARP head studs, ideal for strengthening the valvetrain and head stability. These parts also provide peace of mind for daily driving and spirited use. A well‑balanced combination of cams and spring upgrades ensures durability without pushing it into full race territory.

Fueling, Tune, and Real-World Expectations

Tuning is essential, especially since fuel and timing demands grow with airflow upgrades. Reddit users report 195–205 whp on a “completely stock motor with just a tune and free‑flowing bolt‑ons,” using intake, cat‑back exhaust, and a tune. Upgraded setups with cams and the velocity stack intake approach 230+ whp, though they often require higher fuel pressure (4 bar) or larger injectors. The gains can be dramatic when you commit to fueling properly.

Real-World Commentary and Street Driveability

On Reddit, one enthusiast summed it up like this:

“With a different intake manifold, it is possible to get to 270 wheel, and potentially beyond while staying NA.”
“Even a stock motor with just a tune and free‑flowing bolt‑ons” got 190–205 wheel horsepower on 87 octane (Reddit).

This reflects the sweet spot of FMW’s strategy: offer modular, bolt-on upgrades that progressively elevate performance, from mild street gains to high-output naturally aspirated builds, while keeping reliability and tune-ability.

Every motor and transmission has a weakness. It is very important to address your motor and transmission for weaknesses before modifying them. 

Check with your local laws and regulations before modifying, swiping motors, and transmission..👈

Important Information Before Swapping A Motor And Transmission..👈

The Importance Of Transmission Builds..👈

How To Build A Forged Engine..👈