Honda Civic Si - Powertrain

For the first time in Civic Si history, an advanced turbocharged engine powers the Civic Si Coupe and Si Sedan. An enhanced version of the 1.5-liter 16-valve DOHC direct-injected turbocharged powerplant that powers EX-T, EX-L and Touring Civics, the new Si engine pushes performance on multiple fronts. It's rated at 205 hp at 5700 rpm and offers an impressive 192 lb-ft. of torque between 2100 and 5000 rpm. That's an increase of 31 hp and 25 lb.-ft. of torque, as compared to other 1.5-liter turbocharged Civic models.

The new Si also marks a bold shift in strategy when compared to the previous generation 2015 Civic Si. With a displacement reduction of 36-percent compared with the normally aspirated 2.4-liter engine that powered the previous Si, the new 1.5-liter engine is lighter, more compact and more efficient. With the help of a sophisticated, electronically controlled, intercooled turbocharging system, the new Si offers the same peak 205 horsepower as its predecessor, but at a lower, much more quickly accessible rpm. More important, the new turbo engine offers a decisive peak torque advantage over a far broader rpm range. The result is a highly responsive powertrain that advances the Si's fun-to-drive mission.

Of course, some things have not changed in the new Si. It is still offered exclusively with a 6-speed manual transmission for the maximum in driver control and tactile connection, though the all-new gearbox offers a slicker shift action—and revised ratios to suit the power delivery of the new turbocharged engine. And to help put power to the ground, as in the past, a helical limited-slip front differential is standard.

The Civic Si engine is EPA Tier3/Bin125 and CARB LEV 3/ULEV125 emissions compliant. The new, more efficient engine and transmission, along with improved aerodynamics and a major reduction in running resistance, result in substantially enhanced performance and fuel efficiency, compared to the previous generation (2015) Civic Si 2.4-liter. EPA fuel economy ratings1 are up across the board: 

  • +6 mpg City (+27%)
  • +7 mpg Highway (+23%)
  • +7 mpg Combined (+28%)

Key Powertrain Specifications & Features

Turbocharged 1.5-liter, DOHC direct-injected inline-4 engine *  

  • Dual Variable Timing Control (VTC)
  • Low inertia mono scroll turbo with electronic waste gate* 
  • Computer-controlled Direct Injection (DI) with multi-hole fuel injectors*
  • 10.3:1 compression ratio
  • Lightweight, high rigidity steel crankshaft
  • Drive-by-Wire throttle system
  • Maintenance Minder™ system optimizes service intervals
  • 100,000 +/- miles tune-up interval
  • 205 horsepower at 5700 rpm (SAE net) 
  • 192 lb-ft. torque at 2100-5000 rpm (SAE net) 
  • Premium Unleaded recommended fuel

Emissions/Fuel Economy Ratings

  • EPA Tier3/Bin125 and CARB LEV 3/ULEV125 Emissions compliant 
  • U.S. EPA fuel-economy ratings (city/highway/combined)
    • 28/38/32 mpg1


  • 6-speed Manual
  • Helical Limited-Slip Differential
  • * First for Civic Si

Engine Architecture and Features
Turbocharged 1.5-Liter In-Line 4 Cylinder
The Civic Si's new DOHC 1.5-liter engine is the first turbocharged engine ever to be offered in a Si model. Closely related to the 1.5-liter turbocharged engine available in the 2017 Civic EX-T Coupe and Sedan, the Si powerplant is substantially upgraded to deliver an increase of 31 horsepower and 25 lb.-ft. of torque. With direct injection, low-inertia high-flow mono scroll turbo system with electrical waste-gate and dual Variable Valve Timing Control (VTC), the turbocharged Civic Si powerplant develops the horsepower and torque of a much larger engine.

Turbocharged 1.5-Liter Engine and Intercooler

Compared to the significantly larger normally-aspirated 2.4-liter engine that was standard in the previous-generation Civic Si (model year 2015), the 2017 Si engine develops the same peak horsepower (205) but at a much lower and more quickly accessible rpm (5700 rpm compared to 7000 rpm). The new Si also develops 18 lb.-ft. more peak torque (192), and delivers it over a far greater engine speed range. In the new Si, peak torque hits at just 2100 rpm—less than half the engine speed (4400 rpm) of the previous generation 2.4-liter engine.

Specifically engineered for direct injection and turbocharging, the Si powerplant is designed to offer very high torque output from 2,100 rpm to 5,000 to maximize responsiveness and acceleration without the need for high engine revs. The Si's highly accessible power delivery is a key feature of its immediate power delivery and fun-to-drive nature.

The turbocharged Si 1.5-liter engine is designed to operate on premium unleaded fuel and is rated at 205 horsepower at 5,700 rpm and 192 lb.-ft of torque between 2,100 and 5,000 rpm (SAE net). The Civic Si is rated by the EPA at 28/38/32 mpg1.

Cylinder Block and Crankshaft

The Civic Si's new 1.5-liter inline four has a lightweight die-cast aluminum block with individual reinforced main bearing caps to minimize weight. Cast-in iron cylinder liners provide long-lasting durability. Each journal on the lightweight forged-steel crankshaft is micropolished to reduce internal friction.

Pistons and Connecting Rods  
The 1.5-liter engine's pistons help maintain stable combustion and contribute to improved efficiency with "cavity-shaped" crowns. The lightweight pistons have a carefully optimized skirt design to minimize reciprocating weight, which minimizes vibration and increases operating efficiency. The pistons are cooled by twin oil jets directed at the underside of each piston crown. A cooling gallery cast into the circumference of each piston helps provide superior heat resistance. Ion-plated piston rings help reduce friction for greater operating efficiency. Lightweight, high-strength steel connecting rods are heat-forged in one piece and then "crack separated" to create a lighter and stronger rod with an optimally fitted bearing cap.

Cylinder Head and Valvetrain
The direct-injected Civic Si 4-cylinder turbocharged engine has a lightweight DOHC cylinder head that is made of pressure-cast aluminum alloy. With exhaust port cast directly into the cylinder head, the need for a traditional separate exhaust manifold is eliminated. Compared to other 1.5-liter Civic turbocharged engines, which have a 10.6:1 compression ratio, the Civic Si has a lowered 10.3:1 ratio to allow it to reliably operate at a higher maximum boost pressure of 20.3 psi (16.5 psi on Civic EX-T).

A low-friction, silent-chain drives dual overhead cams and four valves per cylinder. The cam drive is maintenance free throughout the life of the engine. To help further reduce weight, thin-wall hollow camshafts are used.

To benefit fuel efficiency, emissions and power, the turbo engine utilizes sodium-filled exhaust valves. A hollow chamber within the valve contains sodium that is cooled by the exhaust-port cooling jacket. As the chamber reaches close to the valve head, the sodium helps to cool the entire valve. As the valve is internally cooled it doesn't need the enriched fuel mixture that was generally used in turbo engines to help cool the exhaust valve. The resultant leaner mixture reduces emissions, increases fuel efficiency and helps increase power.

The cylinder head includes smaller M12 sparkplugs, down from the more common M14, to save space and weight. The head also includes direct-injection multi-hole fuel injectors with a small diameter bore. Higher-pressure direct injection optimizes fuel atomization, allowing for more efficient combustion. To provide a high-tumble intake charge that further enhances combustion efficiency, both the intake port and piston crown have special designs.

The Civic Si turbocharged engine features Variable Valve Timing Control (VTC) that can vary the timing of both the intake and exhaust camshafts independently. With the turbo engine's variable cam timing, the cam timing can be optimized to suit the driving conditions. Under light loads, valve overlap can be increased to reduce pumping losses and improve fuel efficiency. When engine speed is low and engine load is large, such as during initial acceleration, the amount of overlap is increased to boost the scavenging effect, which improves torque and responsiveness. When engine speed is high and engine load is also high, such as during full-throttle acceleration, the amount of valve overlap is reduced to increase engine output by improving both intake and scavenging.

Direct Injection System
The direct-injection system enables increased torque across the engine's full operating range along with higher fuel efficiency. The system features a compact, high-pressure, direct-injection pump that allows both high fuel flow and pulsation suppression, while variable pressure control optimizes injector operation. A multi-hole injector delivers fuel directly into each cylinder (not to the intake port, as in conventional port fuel injection designs), allowing for more efficient combustion.

The multi-hole injectors can create the ideal stoichiometric fuel/air mixture in the cylinders for good emissions control. Theoretically, a stoichiometric mixture has just enough air to completely burn the available fuel. Based on the operating conditions, the direct-injection system alters its function for best performance. Upon cold engine startup, fuel is injected into the cylinders on the compression stroke. This creates a weak stratified charge effect that improves engine start-up and reduces exhaust emissions before a normal operating temperature is reached.

Once the engine is fully warmed up, fuel is injected during the intake stroke for maximum power and fuel efficiency. This helps create a more homogeneous fuel/air mix in the cylinder that is aided by the high-tumble intake port design. This improves volumetric efficiency, and the cooling effect of the incoming fuel improves anti-knock performance.

Low Inertia Mono Scroll High-Flow Turbo System with Electronic Wastegate

Civic Si’s Turbocharger highlighted with “Hot” and “Cold” Airflow Paths

The turbocharged Civic Si engine employs a unique high-flow, high capacity turbo for maximum responsiveness. The Mono scroll housing design helps the turbo build boost even at relatively small throttle openings and low rpm. The electrically actuated wastegate allows boost pressure to be precisely controlled. With its lower compression ratio, the Civic Si's maximum boost pressure has been elevated to 20.3 psi (from 16.5 psi in Civic EX-T), substantially increasing maximum horsepower and torque.

A large air low-restriction intercooler is positioned low in the front of the car where it receives unobstructed airflow when the vehicle is in motion. Intake air travels from the air filter, to the turbo compressor, on to the intercooler, then to the engine's intake ports. The intercooler helps reduce the temperature of air entering the engine, making it denser for greater performance. To reduce weight, the turbo system is plumbed with rigid, lightweight resin composite inlet pipes to carry intake air to and from the intercooler.

Friction Reducing Technology
The Civic Si's engine makes use of friction-reducing technologies designed to improve engine efficiency. The outer skirts of lightweight aluminum pistons feature a low-friction coating applied in a unique pattern application. The result is reduced overall friction as the pistons move within the cylinder bores. Plateau honing further lowers the friction level between the pistons and the cylinders by creating an ultra-smooth surface. Plateau honing is a 2-stage machining process that uses two grinding processes instead of the more conventional single honing process. This also enhances the long-term wear characteristics of the engine. Low viscosity oil (0W-20) also reduces friction. Other contributors to overall operating efficiency are a special two-stage oil pump relief valve, low-friction oil seals, special low-drag piston ring design, low-friction cam chain and a lightweight crankshaft.

Drive-by-Wire Throttle System
The Civic Si's Drive-by-Wire throttle system replaces a conventional throttle cable with smart electronics that "connect" the accelerator pedal to a throttle valve inside the throttle body. The result is less under-hood clutter and lower weight, as well as quicker and more accurate throttle actuation. Plus, a specially programmed "gain" rate between the throttle pedal and engine offers improved drivability and optimized engine response to suit specific driving conditions.

Honda's Drive-by-Wire throttle system evaluates the current driving conditions by monitoring throttle pedal position, throttle valve position, engine speed (rpm) and road speed. This information is used to define the throttle control sensitivity that gives the Civic Si's throttle pedal a predictable and responsive feel that meets driver expectations.

With the Civic Si's drive mode selector positioned on the center console, the driver can choose between NORMAL and SPORT modes. In SPORT mode, the Si's Drive-by-Wire throttle system has a more aggressive profile targeted at performance driving.

Emissions Control
The Civic Si's engine meets the tough EPA Tier3/Bin125 and CARB LEV 3/ULEV125 emissions standards, and is certified to this level of emissions performance for 150,000 miles.

100,000+/- Mile Tune-up Intervals
The Civic Si's powerplant requires no scheduled maintenance for 100,000+/- miles or more, other than periodic inspections and normal fluid and filter replacements. The first tune-up includes water pump inspection, valve adjustment, and the installation of new spark plugs.

Maintenance Minder™ System
To eliminate unnecessary service stops while ensuring that the vehicle is properly maintained, the Civic Si has a Maintenance Minder™ system that continually monitors the vehicle's operating condition. When maintenance is required, the driver is alerted via a message on the Driver Information Interface (DII). (See the Interior Section for more information.)

6-Speed Manual Transmission
In keeping with the Si's enthusiast driver tradition, just one transmission is available, a quick-shifting 6-speed manual transmission (6MT). The unit offers smooth and precise shift feel and great efficiency. Compared to the closely related 6-speed manual transmission offered in the Civic EX-T, the Si transmission has more rigid bracket mounts to match the engine's higher horsepower and torque. Refinements to the shift linkage and selector mechanism produce a precise and smooth gear lever shift action while reducing stroke by 10 percent.

The 10th-generation Civic 6-speed manual transmission has been carefully engineered to deliver state-of-the-art performance and shift action, with reduced internal friction, tighter internal tolerances and improved synchronizers. The transmission also has a more rigid aluminum exterior case, higher-capacity ball bearings, stiffer gear shafts, and greater torque capacity – compared to the previous Civic Si transmission. A constant-mesh helical reverse gear mechanism significantly reduces noise when reverse is selected. A reverse lockout feature prevents the transmission from accidentally being shifted into reverse while the car is moving forward.

Manual Transmission Gear Ratio Comparison

Gear Ratio (X:1)

2015 Civic Si

2017 Civic EX-T
1.5L Turbo

2017 Civic Si
1.5L Turbo





























Final Reduction Ratio




Powertrain Feature Comparison


2015 Civic Si

2017 Civic EX-T
1.5L Turbo

2017 Civic Si
1.5L Turbo

Engine Type


L-4 Turbocharged

L-4 Turbocharged

Displacement (cc)




Horsepower @ rpm (SAE net)

205 @ 7000

174 @ 5500

205 @ 5700

Torque (lb-ft @ rpm SAE net)

174 @ 4400

167 @ 1800-5500

192 @ 2100-5000

Bore and Stroke (mm)

87.0 x 99.0

73 x 89.5

73 x 89.5

Compression Ratio




Maximum Boost Pressure (psi)




Fuel Injection




Programmed Fuel Injection (PGM-FI)




16-Valve DOHC i-VTEC®

16-Valve DOHC
w/ VTC

16-Valve DOHC
w/ VTC

Drive-by-Wire Throttle System

Low-Inertia MONO Turbocharger


Variable Intake Valve Lift



Intake/Exhaust Variable Cam Timing





Helical Limited-Slip Differential


Front Wheel Drive

100K +/- Miles No Scheduled Tune-Ups

Fuel Economy and Emissions Ratings


2015 Civic Si

2017 Civic EX-T 1.5L Turbo

2017 Civic Si
1.5L Turbo

EPA Fuel Economy Ratings1

22/31/25 (6MT)

31/42/35 (6MT)

28/38/32 (6MT)

Recommended fuel

Premium Unleaded

Regular Unleaded

Premium Unleaded

CARB emissions rating




(See the Specifications and Features section for all data.)

1Based on 2017 EPA fuel-economy ratings. Use for comparison purposes only. Your mileage will vary depending on how you drive and maintain your vehicle, driving conditions and other factors.