Introduction: Picking the Right Turbo for 700 Horsepower

Achieving 700 horsepower from a diesel engine is an ambitious goal that demands careful component selection, and the turbocharger is the single most influential piece of the puzzle. The turbo must supply enough airflow to support that power target without creating excessive backpressure or lag that ruins drivability. Two manufacturers dominate the aftermarket diesel scene: Garrett Motion and BorgWarner. Both offer turbos capable of 700 hp, but their design philosophies, wheel technologies, and housing options produce very different driving experiences. This article provides a detailed comparison of the most suitable Garrett and BorgWarner models for 700 hp builds, explains the sizing theory behind each choice, and covers the supporting modifications needed to realize that power reliably.

Turbocharger Sizing Fundamentals

Before comparing specific models, it helps to understand the variables that determine turbo sizing. The compressor and turbine each have key parameters that influence performance.

Compressor Map and Flow Rate

A compressor map plots pressure ratio against airflow (usually in lb/min or m³/s). For 700 hp on a diesel engine, you typically need roughly 60–75 lb/min of airflow (depending on BSFC and boost levels). The map also shows the efficiency islands. Operating in the 70–78% efficiency area keeps charge temperatures low and reduces the risk of detonation. The inducer and exducer diameters, along with the trim (ratio of inducer to exducer diameter), determine how much air the wheel can move.

Turbine Housing and A/R Ratio

The turbine housing’s A/R (area/radius) ratio controls exhaust gas velocity and backpressure. A smaller A/R spools faster but restricts top-end flow; a larger A/R reduces backpressure at high RPM but increases lag. For a 700 hp street diesel, a mid-range A/R (e.g., 1.00–1.25 on a BorgWarner S400) often provides a good balance. The turbine wheel itself also matters—divided or undivided housings affect pulse separation for twin-scroll manifold designs.

Wastegate and Boost Control

Large turbos can overboost if not controlled. An external wastegate (typically 40–50 mm) is recommended for precise boost management. Internal wastegates on very large housings may be inadequate. Many 700 hp builds use an external gate even when the turbo is offered with an internal option.

Supporting Modifications That Affect Turbo Choice

The turbo you choose must work with your fuel system, intercooler, and engine head. High-pressure common rail injection capable of delivering enough fuel for 700 hp typically demands larger injectors and a higher-flowing CP3 or CP4 pump. An air-to-air or air-to-water intercooler must keep intake temperatures below 130–140°F (54–60°C) to avoid heat soak. Even the best turbo is wasted if the engine can’t ingest or reject heat effectively.

Garrett Turbochargers for 700 HP Builds

Garrett has produced turbos for decades and their GTX and G Series ranges are favourites among diesel tuners. For 700 hp, the most common candidates are the GTX4718R and GTX5533R. Both use dual-ball-bearing cartridges, billet compressor wheels, and Garrett’s latest aerodynamics.

Garrett GTX4718R

This turbo uses a 71 mm compressor inducer and a 66 mm turbine wheel. It flows approximately 72 lb/min, placing it right at the 700 hp threshold on a well-tuned common-rail diesel. Its 0.84 or 0.95 A/R turbine housing option offers quick spool for a 6.7L or larger engine. The dual ball bearing design reduces friction and allows the turbo to reach full boost as low as 2500–2800 RPM, which is excellent for street driving. Many 6.7L Cummins builds run the GTX4718R to produce around 680–720 hp with the right fuel and tuning.

Garrett GTX5533R

Stepping up, the GTX5533R uses a 76 mm compressor inducer and flows about 85 lb/min. This is a 900+ hp turbo when pushed, but it can be dialled back for a 700 hp target, running comfortably within its efficiency island. The larger wheel comes with slightly slower spool—full boost might not arrive until 3200 RPM. That makes it better suited for engines with large displacement (6.7L+) or for those planning future upgrades beyond 700 hp. The GTX5533R pairs well with a rebuilt transmission and supporting fuel mods because the extra air capacity reduces drive pressure and EGTs at high load.

For more details, see Garrett’s official product pages: Garrett Performance Turbochargers.

BorgWarner Turbochargers for 700 HP Builds

BorgWarner’s diesel lineup includes the popular S400SX (and S400SX4) family, as well as the EFR 7670. Both are known for robust construction and innovative turbine housing designs.

BorgWarner S400SX (67 mm inducer)

The S400SX-67 is a classic choice for 650–750 hp. It uses a 67 mm compressor inducer and a 73 mm turbine wheel. The SX casting features a more efficient compressor cover and a higher-flowing turbine compared to the older S400. With a 1.10 or 1.25 A/R housing, this turbo can support 700 hp on a 6.7L Cummins or 7.3L Power Stroke. Spool is slightly slower than a comparable Garrett, but the BorgWarner often carries a lower price point and is very forgiving on exhaust restrictions. Many builders pair it with a 5-inch exhaust and external wastegate for clean top-end breathing.

BorgWarner EFR 7670

The EFR (Engineered For Racing) line uses gamma-Ti turbine wheels, which are lighter and stronger than standard Inconel. The EFR 7670 has a 76 mm compressor inducer and can flow over 80 lb/min, making it capable of well over 700 hp. The turbine housing offers multiple porting options for anti-surge and a built-in wastegate that is surprisingly effective for mid-range boost control. The EFR’s spool characteristic is excellent due to the lightweight wheel and dual ball bearings. However, the EFR 7670 is a physically tight fit in some engine bays, and the turbine housing tends to run hotter due to the titanium’s thermal properties. It is a favourite in high-end street and competition builds where weight and response matter.

For a complete list of BorgWarner S400SX specs, refer to the manufacturer’s documentation: BorgWarner Turbo Technologies.

Head-to-Head Comparison: Garrett vs BorgWarner

Now that we have covered the prime candidates, let’s compare them across the factors that matter most for a 700 hp street-legal diesel.

  • Spool Time and Response: Garrett’s GTX4718R spools faster than any BorgWarner in this range, often reaching full boost 300–400 RPM earlier. The EFR 7670 is close, but the larger housing needed for 700 hp sacrifices some low-end. If towing or daily driving with frequent low-RPM load is part of your use, the Garrett dual-ball-bearing design wins.
  • Top-End Airflow and Power Ceiling: The GTX5533R and EFR 7670 both have headroom beyond 700 hp. The BorgWarner S400SX-67 is more tightly matched to the 700 hp target—it will be very efficient at that power but may run out of steam above 800 hp. The Garrett GTX4718R also sits near its limit at 700 hp, so the S400SX-67 is a great option if you intend to stay right at 700 hp.
  • Durability Under Extreme Conditions: BorgWarner’s S400 series is renowned for taking abuse—over-speed events, high drive pressures, and occasional detonation. The cast iron turbine housing can withstand heat cycling better than some Garrett offerings. The Garrett GTX series with dual ball bearings is very reliable when properly installed and oiled, but the bearings can be damaged by oil contamination or extreme shaft speeds. The EFR’s titanium wheel is almost indestructible under normal use, but it is expensive to replace.
  • Price and Availability: The S400SX-67 is significantly cheaper than the Garrett models—often 30–40% less. The EFR 7670 is in the same price range as the GTX5533R. If budget is a primary concern, the BorgWarner S400 family offers the best value for a proven 700 hp turbo. Keep in mind that support for BorgWarner parts (such as rebuild kits and different turbine housings) is widely available through diesel performance vendors like Diesel Power Products.
  • Ease of Integration: Many aftermarket manifolds are designed around the Garrett T4 or T6 flanges. The GTX4718R and GTX5533R come with standard T4 or T6 inlets, making them a drop-in upgrade for common diesel platforms. BorgWarner’s S400 uses an S400 flange, which may require an adapter or a custom manifold. The EFR 7670 has a unique V-band inlet and outlet, simplifying piping but limiting exhaust choice.

Supporting Modifications: The Turbo Is Just One Piece

A 700 hp turbocharger will only deliver its potential if the rest of the system is ready. Here are the essential supporting upgrades:

  • Fuel System: The CP3 pump (or CP4) must be modified to supply higher rail pressure and volume. Upgraded injectors (usually 50–75% over stock) and a larger fuel rail or lines are typical. For common-rail engines, a good tuner can dial in the injection timing to match the turbo’s air delivery.
  • Intercooler and Charge Piping: A large air-to-air intercooler (25–30 sq in of core) or an air-to-water unit is mandatory. Charge piping should be 3–3.5 inches in diameter to minimize pressure drop. Silicone couplers with T-bolt clamps prevent blow-offs.
  • Exhaust System: A 4-inch downpipe is the minimum; 5-inch is better for 700 hp. The exhaust must flow freely to reduce drive pressure on the turbine. A quality external wastegate (e.g., Tial 44 mm or 50 mm) should be plumbed to the crossover pipe or manifold to control boost spikes.
  • Engine Internals: While stock diesel bottom ends can handle 700 hp for a while, forged pistons, upgraded connecting rods, and head studs are recommended for reliability. A six-cylinder Cummins or Duramax can survive stock rods at this power with conservative tuning, but the margin for error is thin.
  • Transmission and Drivetrain: An automatic transmission (48RE, Allison 1000) will need a billet torque converter, valvebody upgrade, and possibly a gear set. Manual transmissions require a heavy-duty clutch and possibly a gear change for driveability.

Single vs Compound Turbocharging for 700 HP

All the turbos discussed above are used in single-turbo configurations. However, many street-driven diesel trucks achieve 700 hp with compound turbo setups (e.g., an S300 over an S400 or a Garrett GTW over a GTX). Compounds offer unparalleled spool and airflow, but they add complexity, weight, and cost. For a 700 hp target that still needs towing capacity and rapid response, compounds are a strong option. A single large turbo (like the GTX5533R or EFR 7670) can work well if the engine is built for high RPM and the vehicle is primarily used for street or drag racing. If you want responsive torque for daily driving or towing, a compound kit might be the better investment despite the higher price.

For a detailed explanation of compound turbo selection, refer to this technical guide: Engine Basics: Compound Turbo Systems.

Making the Final Choice

There is no single “best” turbo for 700 hp—the right selection depends on your specific engine platform, intended use, and budget.

  • If you prioritize fast spool for street use and are willing to spend more, the Garrett GTX4718R is an excellent choice. Pair it with a well-matched A/R housing (0.95 for 6.7L, 1.10 for larger engines) and a good intercooler.
  • If you want a proven, cost-effective turbo that can take punishment, the BorgWarner S400SX-67 delivers reliable 700 hp with a 1.10 or 1.25 housing. It may spool later, but it is forgiving and easy to tune.
  • If you plan to push beyond 700 hp eventually, the GTX5533R or EFR 7670 provide headroom for 800–900 hp without changing turbos.
  • If you need towing capability with 700 hp, consider a compound setup. A single large turbo won’t satisfy low-RPM torque demands.

Ultimately, work with a reputable diesel tuner who can model your compressor map and recommend the exact turbine housing and wastegate sizing. A turbo that is too large will lag and overboost; one that is too small will choke the engine and melt EGTs. With the correct selection, a 700 hp diesel can be both powerful and reliable for many miles.