What Is a 68-Trim Turbo and Why It Matters for Your RSX

The Acura RSX, particularly the Type-S with its K20 engine, remains a favorite platform for forced induction. Among the many turbocharger options, the 68-trim turbo occupies a sweet spot that balances spool response with top-end power. Unlike generic “T3/T4” labels, the trim number refers to the ratio of the turbine inducer diameter to the compressor exducer diameter—in this case, a 68mm compressor wheel with a specific A/R (area/radius) configuration. This results in a compressor map that delivers strong mid-range torque while still allowing the engine to breathe at higher RPM, making it ideal for street-driven RSXs that see occasional track use.

How Trim Size Affects Performance

Trim is a measure of the compressor wheel’s geometry. A 68-trim wheel has a larger inducer relative to the exducer than a 57-trim, meaning it can move more air at higher boost pressures. However, it is not as large as a 70- or 76-trim, which would require extensive engine work and sacrifice low-end response. On a K20, the 68-trim turbo typically spools fully by 3,800–4,200 RPM, providing a broad power band that feels linear and controllable.

  • Compressor map efficiency: Peak efficiency island often falls between 15–25 PSI, matching the RSX’s stock compression ratio.
  • Wheel material: Many 68-trim units use billet compressor wheels for reduced inertia and faster spool.
  • Housing options: A 0.63 A/R turbine housing is common for street use; a 0.82 A/R shifts power higher for drag racing.

Real-World Power Gains and Dyno Expectations

When properly supported, a 68-trim turbo can push an RSX past the 350–400 wheel horsepower mark. The exact number depends on fuel choice, boost level, and engine condition. With pump gas (93 octane) and conservative tuning, expect 320–350 whp on a Dynojet. Adding ethanol (E85) or race fuel can vault the car into the 400+ whp range without internal engine modifications, provided the tune is conservative.

Torque Curve and Driveability

Unlike small-frame turbos that fall off at high RPM, the 68-trim maintains pull past 7,500 RPM. Torque comes on progressively rather than hitting like a switch, which helps traction and drivetrain longevity. A properly tuned setup will yield a flat torque curve from 4,500 to 7,000 RPM, making the car feel faster than the peak number suggests.

Dyno Plot Example (K20A2, 9.5:1 compression)

  • 2,500 RPM: 180 whp, 210 lb-ft
  • 4,000 RPM: 270 whp, 340 lb-ft
  • 6,000 RPM: 340 whp, 330 lb-ft
  • 8,000 RPM: 310 whp, 280 lb-ft

These numbers assume a 3-inch exhaust, front-mount intercooler, and a calibrated ECU. Without these supporting mods, the turbo will not reach its potential.

Reliability: What It Takes to Keep Your RSX Alive

A turbocharger adds stress to every system in the car. The 68-trim’s moderate size actually improves reliability compared to larger frames because it does not demand as much fuel or cooling at lower boost. However, reliability is not automatic—it requires attention to oiling, heat management, and engine internals.

Engine Build Requirements

For 350 whp and below, the stock K20 bottom end with upgraded rod bolts can survive. Beyond that, forged pistons and rods become necessary. The stock cast pistons are brittle under high cylinder pressure, and the ring lands are prone to failure above 380 whp. A forged set (e.g., CP or JE) with a 9.0:1 compression ratio allows higher boost on pump gas while maintaining good street manners.

  • Rod bolts: ARP 2000 or L19 are cheap insurance even on stock rods below 400 whp.
  • Head studs: ARP head studs prevent head lift at elevated boost levels.
  • Oil pump: A K20 oil pump gear upgrade (or aftermarket billet unit) prevents gear failure at high RPM.

Oiling and Cooling

The turbocharger itself must receive clean, pressurized oil. Use a -3AN or -4AN line with a restrictor if the turbo has a journal bearing; ball bearing turbos can use a larger feed but often need a restrictor to avoid blowing seals. A dedicated turbo drain line returning to the oil pan above the oil level is critical. Additionally, an oil cooler for the engine is highly recommended if you drive aggressively. Water-cooled center sections (common on modern 68-trim units) help reduce coking after shutdown.

Heat Management Checklist

  • Wrap or coat the exhaust manifold and downpipe to keep under-hood temperatures down.
  • Use a high-flow radiator (Koyo or Mishimoto) with dual fans.
  • Install a turbo blanket to reduce radiant heat to the intake and valve cover.
  • Relocate the intake air filter to a cooler location, ideally behind the bumper.

Tuning the RSX with a 68-Trim Turbo

Tuning is where most RSX turbo builds succeed or fail. The stock ECU can be recalibrated via Hondata KPro or K-Tuned, both of which give full control over fuel, ignition, and boost control. A custom tune on a dyno is strongly preferred over off-the-shelf maps because every engine and turbo combination reacts differently to airflow.

Tuning Parameters to Watch

The 68-trim’s compressor flow curve means that boost creeps can occur if the wastegate is too small or the turbine housing is incorrect. A good tuner will look at:

  • Air/fuel ratio: Target 11.5–12.0 on pump gas under boost.
  • Ignition timing: Conservative timing (10–15 degrees at peak boost) helps prevent detonation.
  • Boost control: A manual boost controller or electronic solenoid (e.g., MAC valve) allows precise boost adjustment.
  • Fuel pressure: Ensure the pump maintains pressure under high load. A Walbro 255 or AEM 340 pump is sufficient for 400 whp.

Common Tuning Pitfalls

  • Using a basemap from a different turbo size (57-trim maps are too lean for a 68-trim).
  • Ignoring fuel trims at low load, causing surging and poor idle.
  • Setting boost cut too high without verifying fuel system capacity.

Supporting Modifications: The Complete Package

Bolting a 68-trim turbo to an otherwise stock RSX will yield disappointing results. The following upgrades are considered mandatory for a reliable street build.

Fuel System

  • Injectors: 750–1000cc high-impedance injectors (ID, FIC, or Bosch).
  • Fuel pump: Drop-in 255 LPH or 340 LPH pump. For E85, a 450 LPH pump or dual pump setup is required.
  • Fuel pressure regulator: A return-style regulator (Aeromotive, Radium) if you exceed the stock FPR’s capacity.

Intake and Exhaust

  • Intercooler: At least 3” core thickness, 24” width, with aluminum end tanks. A treadstone or PRL copy works well.
  • Charge piping: 2.5” aluminum piping with silicone couplers and T-bolt clamps.
  • Blow-off valve: A recirculating or vent-to-atmosphere valve set for 15–25 PSI. Tial Q or HKS SSQV are common choices.
  • Downpipe: 3” mandrel-bent downpipe with a high-flow catalytic converter if you want to pass emissions.
  • Exhaust: 3” cat-back system (HKS, GReddy, or custom). Stock RSX exhausts are too restrictive for turbo applications.

Drivetrain and Suspension

With 350+ whp, the stock clutch will slip. A stage 2 or 3 clutch (ACT, Exedy, Competition Clutch) and lightweight flywheel improve engagement. The stock LSD in the Type-S is adequate but can be upgraded to a helical unit for better traction. Wider tires (235/40R17 or 255/40R17) reduce wheelspin in first and second gear.

Cost Breakdown and Installation Considerations

A 68-trim turbo kit for the RSX typically costs between $2,500 and $4,500 for the turbo, manifold, wastegate, blow-off valve, and intercooler piping. Adding injectors, pump, clutch, and tuning brings the total to $5,500–$8,000 for a reliable 350 whp setup. If you build the engine, add another $2,000–$4,000 for pistons, rods, machine work, and assembly.

DIY vs. Professional Installation

Experienced mechanics can install a turbo kit in a weekend, but tuning requires a dyno session. If you have never installed a turbo, budget for a shop to do the exhaust manifold studs, oil feed/drain, and wiring for boost control. Mistakes in oil routing can destroy the turbo in minutes.

Comparing the 68-Trim to Other Options

The 68-trim is not the only choice for an RSX. Here is how it stacks up against common alternatives:

  • 57-trim (e.g., Garrett GT2871R): Faster spool (full boost by 3,000 RPM), but runs out of airflow above 330 whp. Best for autocross or stock-engine builds.
  • 70-trim (e.g., Precision 5858): Lags to 4,500 RPM but supports 450–500 whp. Requires built internals and larger injectors.
  • 76-trim (e.g., Garrett GT3076R): Track-focused with spool above 4,800 RPM. Not ideal for daily driving.

The 68-trim offers the widest usable power band for a street car that sees highway pulls and occasional lapping days. It is forgiving enough for a tuned stock engine but has headroom for future upgrades.

Maintenance After the Build

A turbocharged RSX demands stricter maintenance. Change oil every 3,000 miles with a quality synthetic (5W-30 or 5W-40 depending on climate). Inspect the boost pipes for leaks monthly; a loose coupler can cause a lean condition. Watch for excessive smoke from the exhaust, which indicates failing turbo seals or a restricted oil return line. Keep an eye on coolant temperatures during summer stop-and-go traffic—an upgraded fan switch or lower-temperature thermostat helps.

Final Thoughts: Is the 68-Trim Turbo Worth It?

For RSX owners who want a dramatic improvement in power without turning the car into a garage queen, the 68-trim turbo is a proven choice. When combined with proper tuning and supporting modifications, it delivers the kind of performance that makes the RSX feel like a modern sports car. The key is to avoid cutting corners on fuel delivery and engine management—those two areas make or break reliability. With careful planning, a 68-trim RSX can be both a thrilling daily driver and a reliable weekend warrior.

For further reading, check out Hondata’s K-Series tuning guide or Precision Turbo’s compressor maps to visualize flow characteristics. Community forums like ClubRSX Forced Induction section offer real-world build threads and troubleshooting advice.