- VTEC® technology is a part of Acura's high-performance history and remains a key component in the brand's vehicles
- VTEC® was the first commercially successful variable valve timing and lift technology used in a production car
- Various uses for VTEC® technology have evolved to provide new benefits, including increasing horsepower and torque, and improving fuel efficiency
Variable Valve Timing and Lift Electronic Control, or VTEC®, made its debut in the late 1980s as a way to extract maximum horsepower and torque from smaller displacement engines. As the first practical, reliable and commercially successful variable valve timing and lift technology, VTEC® spurred an industry-wide movement to use variable valve timing in engines. It has been at the heart of Acura's best-performing models for nearly forty years.
Today, VTEC® has evolved to include specialized applications designed to improve fuel efficiency and emissions, as well as add power. Originally an alternative to turbochargers, today VTEC® is used in conjunction with turbos for maximum responsiveness and power, all while helping vehicles meet strict emissions and fuel economy standards in the U.S. and around the world.
History of VTEC®
In 1984 Honda launched the New Concept Engine (NCE) program to increase the horsepower and torque produced from its small displacement engines. The program led to the development of 4-valve per cylinder double overhead cam (DOHC) engines that debuted in Honda and Acura automobiles at the time, including the 1986 Acura Integra in the U.S.
Traditionally, high-revving four-valve-per-cylinder engines sacrificed low-rpm torque to produce high-revving horsepower. The intricate relationship between the timing, lift, and duration of intake and exhaust valves set to produce high-revving horsepower generally hurts low-rpm torque. Resetting the valvetrain and retuning an engine for low-rpm torque would do so at the expense of high-end horsepower.
Ikuo Kajitani, a Honda engineer at Honda's Tochigi R&D Center, recognized that the solution to this problem was to create a mechanism that could alter the timing and lift of the valves so low-rpm torque wouldn't be sacrificed for high-end power, or vice versa. This led to the development of Variable Valve Timing and Lift Electronic Control, or VTEC®.
Mechanics of a VTEC® Engine
At the core of early VTEC® engines was a camshaft featuring three different cam lobes for each pair of valves. The two outer cams were tuned for low-rpm torque and smooth idle, while the center cam was tuned for high-revving horsepower. Each cam had its own rocker arm, but only the outer two pressed against the valves, with the central rocker arm assigned only to the center cam.
At low engine speeds, the two outer cams were used to open and close the valves, with the center cam inactive, since its rocker arm wasn't directly attached to the valvetrain. However, as revs increased, the engine computer signaled a spool valve to direct oil pressure to activate a pin that locked the two outer rocker arms to the arm in the center. This forced the two outer arms to act upon the center cam, which featured a longer duration, higher lift, and timing optimized for high-rpm horsepower.
VTEC® made its commercial debut on the 1989 Integra XSi in Japan, with stunning results. Active on both the intake and exhaust cams of this DOHC 1.6-liter engine (B16A), it produced 160 horsepower at an incredible 7,600 rpm. The broad torque curve peaked at 111 lb.-ft. at 7,000 rpm but offered most of that torque well below that lofty figure.
Multiple variations of VTEC® have been created over the decades to improve horsepower and torque while lowering emissions and increasing fuel efficiency. The various permutations include VTEC-E®, i-VTEC® with Variable Cylinder Management™ (VCM®), pairing VTEC® with turbochargers, and i-VTEC® with Variable Timing Control™ (VTC™).
VTC™, while strictly not VTEC® since it doesn't alter the lift or duration of the valves, has often been used together with VTEC® since VTC™ was Introduced in the early 2000s. VTC™ uses a spool to direct high-pressure oil to chambers inside a cam's drive sprocket, allowing for continuous adjustments of the intake camshaft's position relative to the crankshaft.
Known as “phase,” this position could be adjusted over a wide range, depending on engine load and other factors, allowing extremely precise control of valve timing over the engine's entire operating range. When combined with VTEC®, VTC™ allows the optimal balance of power delivery, fuel efficiency and exhaust emissions.
DOHC VTEC® in Some of Acura's Most Iconic Cars
The original DOHC version of VTEC® helped establish several Acura vehicles as performance icons in the 1990s. The iconic nature of VTEC® is due in part to the dynamic of driving cars equipped with DOHC VTEC®. At low RPM, the engines are docile and quiet, but when the VTEC® system crosses to its higher RPM cam – that is, when “VTEC® kicks in,” as the high-lift switchover has become known – the engine note takes on a sharper edge, with an increase in power that's immediately noticeable from behind the wheel.
The first Acura vehicle in the U.S. to use a DOHC version of VTEC® was the 1991 Acura NSX. It developed 270 horsepower and 210 lb.-ft. of torque from its 3.0-liter V6 engine (C30A). In its first year, the NSX garnered an impressive list of accolades, including Motor Trend "Top Ten Performance Cars," Road & Track "Ten Best Cars in the World," Popular Science "Best of What's New," and Popular Mechanics "Design and Engineering Award". In 1997 the NSX's 3.0-liter V6 engine was replaced with a larger, more powerful 3.2-liter DOHC 24-valve V6 (C32B) also with DOHC VTEC® producing 290 horsepower and 224 lb.-ft. torque.
In 1992, the Integra GS-R became the second Acura vehicle to use VTEC®. The coupe was powered by a 1.7-liter DOHC VTEC® (B17A1) engine producing 160 hp and 117 lb.-ft. The first sedan to use VTEC® was the redesigned 1994 Integra GS-R. Available as a coupe or a sedan, it was powered by a 1.8-liter DOHC engine (B18C1) that produced 170 hp and 128 lb.-ft.
In 1997 the Acura Integra Type R was introduced to the United States for the first time, powered by a hand-built version of the acclaimed B-Series engine. The 195-horsepower 1.8-liter DOHC VTEC® four-cylinder (B18C5) revved to an incredible 8,400 rpm and produced 108 horsepower per liter without the use of turbocharging.
These DOHC VTEC® engines were fundamental to the explosion of aftermarket performance parts for Japanese cars in the 1990s, and key to Acura's iconic status with enthusiast drivers. Acura was able to match the power output of competitors without complicated and heavy turbocharging, while still offering excellent drivability and fuel efficiency.
SOHC 4-Cylinder VTEC
The single overhead camshaft (SOHC) version of VTEC® first appeared on Acura vehicles in 1997 with the arrival of the Acura 3.0CL, a sleek two-door coupe. The CL was the first luxury import model designed, engineered and built in United States and it used a 3.0-liter SOHC VTEC® V6 (K30A1) that produced 200 hp and 195 lb.-ft.
In 1997, Acura also introduced the 2.2CL with a 2.2-liter SOHC non-VTEC® inline four-cylinder engine (F22B1). The following year it was replaced by the 2.3CL powered by a 2.3-liter SOHC 16-valve VTEC® 4-cylinder (F23A1). Power increased from 145 hp and 147 lb.-ft. to 150 hp and 152 lb.-ft. Fuel economy ratings also increased from 28 mpg to 29 mpg highway.
In 1999, VTEC® debuted in the TL family, with an all-aluminum, 3.2-liter SOHC VTEC® V6 engine (J32A1) that produced both abundant low-rpm torque and exhilarating high-rpm horsepower. The 3.2TL produced 225 hp and 216 lb.-ft. The same 3.2-liter engine was used to power the 3.2CL from 2001 to 2003.
Acura's first high-performance Type S model, the 2001 3.2CL Type S incorporated several engine enhancements including a dual-stage induction system, low-restriction dual-outlet exhaust, larger diameter throttle body, increased compression ratio, special intake valves, camshafts and cylinder heads. Its 3.2-liter V6 engine (J32A2) produced 260 horsepower. The 2002 3.2TL Type S sedan also featured the same performance-tuned 3.2-liter VTEC® engine.
In 2004, the redesigned Acura TL (which replaced the 3.2TL) used an upgraded version of the 3.2-liter VTEC® V6 (J32A3) from the 3.2TL Type-S. The engine now featured an aluminum-alloy cylinder block and heads, and a new crankshaft and pistons. Combining a 3-rocker VTEC® system with a high 11.0:1 compression ratio and high-flow intake and exhaust systems helped the V6 produce 270 hp (10 hp more than the 2003 TL Type-S). It also delivered more torque from 1800 rpm to redline, with 238 lb.-ft maximum torque delivered at 5000 rpm.
A new SUV was added to the Acura lineup in 2001 and with it came a new VTEC® engine. The 2001 Acura MDX featured a 3.5-liter SOHC VTEC® V6 engine (J35A3) that produced 240 hp and 242 lb.-ft. of torque. With the 3.5-liter engine, the MDX was able to establish new performance benchmarks in the SUV category for versatility, responsibility and dynamic performance.
In 2003, the MDX boosted its already formidable performance by updating the 3.5-liter engine (J35A5) and increasing horsepower to 260. In 2004, further updates increased horsepower and torque again to 265 hp and 253 lb.-ft. When the MDX was redesigned in 2007, a new 3.7-liter, SOHC, VTEC® V6 engine (J37A1) developed 300 hp and 275 lb.-ft. At the time, it was the most powerful Acura vehicle ever produced.
Different versions of the 3.5-liter V6 (J35A8) and the 3.7-liter V6 (J37A2) would be used in the Acura RL. A version of the 3.5-liter V6 (J35Z6) was also used in the TSX sedan from 2010 to 2014 and in the TL from 2009 until 2014. From the late 1990s, all the way into the early 2000s, SOHC VTEC® remained a staple in Acura vehicles, appearing in top-line models and providing the dual benefits of improved horsepower and torque with excellent fuel efficiency.
VTEC® For Added Fuel Efficiency
While VTEC® added power, another version of the technology focused primarily on improving fuel efficiency by limited the engine's breathing below 2,500 rpm.
Below that engine speed, one intake valve for each cylinder remains mostly closed. This single intake-valve operation enhances swirl inside the combustion chamber, creating a stratified charge that concentrates the more fuel-rich part of the mixture near the spark plug for better fuel efficiency. Above 2,500 rpm, all the valves open and close fully.
Combined with lean-burn technology, this VTEC® operation made a dramatic difference in fuel economy ratings. Multiple engines used this type of VTEC® mechanism throughout the years, including 2.3CL (F23A1). It was also used on the SOHC 3.0-liter V6 engines in the 3.0CL (J30A1), as well as the 3.5-liter V6 in the MDX (J35A3, J35A5).
Modern i-VTEC® Builds on Decades of Advanced Technology
Implemented in the early 2000s, i-VTEC® is still in use today. i-VTEC® refers to a more intelligent version of VTEC® that incorporates tighter computer integration to the valvetrain mechanism.
Although i-VTEC® is used in both 4-cylinder and V6 engines, the details in each application differ. In Acura 4-cylinder engines i-VTEC® uses a combination of the variable cam lift and duration of VTEC® along with Variable Timing Control™ (VTC™).
DOHC 4-Cylinder i-VTEC® with VTC™
For the 2002 model year, VTEC® was reengineered to incorporate the new Variable Timing Control (VTC™) on the exhaust cam of DOHC VTEC® engines. The technology debuted in the 160-hp Acura RSX (K20A3) and the 200-hp Acura RSX Type S (K20A2).
Both engines use the cam-switching feature of the original VTEC® engines, however, the K20A3 use it solely on the intake cam, while the K20A2 use it on both intake and exhaust cams. In 2005, the RSX Type S received a power boost to 210 horsepower. A larger 2.4-liter version of the K-Series engine in the 2004 Acura TSX (K24A2) produced similar horsepower output, but additional torque.
Throughout the 2000s and much of the 2010s, variations of this naturally-aspirated 2.4-liter engine, improved through the use of direct-injection were the standard 4-cylinder powerplant in many Acura models. In 2013, a high-performance variant (K24Z7) debuted in the Acura ILX, initially with 201 hp, and later 205 hp.
The 272 hp 2.0-liter turbocharged engine in both the third-generation Acura RDX (K20C4) and the second-generation TLX (K20C6) features an i-VTEC® system that uses VTC™ on both the intake and exhaust cams, and VTEC® on the intake cam. The use of VTC™ on both cams adds another layer of efficiency and control to combustion, allowing precise timing of valve opening and closing for improved power and a smooth idle.
SOHC V6 i-VTEC® with VCM®
Fuel efficiency has always been an Acura hallmark, and in 2005 VTEC® was again modified with a new technology, Variable Cylinder Management™ (VCM®). Depending on throttle position, speed, and engine load, VCM® shuts down half of the cylinders, effectively turning a V6 into an inline-3 cylinder.
Although also called i-VTEC, the system used on the V6 engines does not include a cam-phasing mechanism as on four-cylinder application. Instead, i-VTEC® with VCM® uses traditional VTEC® cam-switching for low-rpm torque and high-end horsepower combined with the added benefit of shutting down the engine's rear bank of cylinders to increase fuel efficiency in certain driving situations.
The VCM® system can tailor the working displacement of the engine to match the driving requirements from moment to moment. Since the system automatically closes both the intake and exhaust valves of the cylinders that are not used, pumping losses associated with intake and exhaust are eliminated and fuel efficiency gets a further boost. The system combines maximum performance and maximum fuel efficiency — two characteristics that don't typically coexist in conventional engines.
VCM® monitors throttle position, vehicle speed, engine speed, automatic-transmission gear selection and other factors to determine the correct cylinder activation scheme for the operating conditions. In addition, the system determines whether engine oil pressure is suitable for VCM® switching and whether catalytic-converter temperature will remain in the proper range.
To further smooth the transition of activating or deactivating cylinders, the system adjusts ignition timing and throttle position and turns the torque converter lock-up on and off. As a result, the transition between 3- and 6-cylinder modes is effectively unnoticeable to the driver.
When under light load, VTEC® switches these cylinders to a cam with zero lift, closing the intake valves completely. This, along with cutting fuel to the injectors on the affected cylinders, shuts them down almost completely; the spark plug continues to fire to maintain heat in the plug for when the cylinders are restarted.
Both the first-generation MDX (J35A3/J35A5) and second-generation MDX (J37A1) featured a SOHC 3.7-liter V6 with VTEC®. A 290 hp SOHC 3.5-liter V6 (J35Y5) with i-VTEC® and VCM® is found under the hood of every third- and fourth-generation MDX, with two notable exceptions:
- The MDX Sport Hybrid, sold from 2017 to 2020, featured a 321 hp 3.0 liter, 24-valve, SOHC V6 gas engine (J30Y1) with i-VTEC® valvetrain paired with three electric motors. Instead of VTEC® and VCM®, the Sport Hybrid used battery electric power and the cam-switching feature of the original VTEC® engines solely on the intake cam.
- The 355 hp turbocharged MDX Type-S, introduced in 2022, is powered by a DOHC 3.0-liter V6 (J30AC) that does feature VCM®, but is not equipped with i-VTEC®.
VTEC® and Turbocharging
Using variable valve timing and lift with a turbocharger presents unique opportunities for generating power and improving fuel efficiency. Acura has combined these technologies in multiple ways. The combination of turbocharging, VTC™ and VTEC® also helps smaller displacement engines equal the output of larger non-turbocharged engines with the added benefits of a broader torque curve, a lower rpm torque peak, and sustained power at higher rpm.
Acura combined VTEC®, VTC™ and a turbocharger for the first time in the 2007 Acura RDX. The 2.3-liter four-cylinder (K23A1) used an innovative variable flow turbo that overcame the shortcomings of conventional turbo designs and delivered an unusually broad powerband with little or no lag in throttle response.
At low engine speeds at wide-open throttle, the exhaust uses the low-lift cam, while VTC™ is used to advance the intake and delay the exhaust timing. This high-overlap combination results in optimum scavenging at low speeds. At high engine speeds and wide-open throttle, VTEC® switches to the high-lift cam, while VTC™ reduces overlap as much as possible, reducing pumping losses. The result is excellent boost response at all engine speeds, and outstanding high-RPM power.
Acura has two turbocharged four-cylinder VTEC® engines. The 272 hp 2.0-liter in the third-generation RDX (K20C4) and second-generation TLX (K20C6) features i-VTEC® with VTC™ on both the intake and exhaust cams, and VTEC® on the intake cam. The 200 hp 1.5-liter (L15CA) that powers the 2023 Acura Integra also combines turbocharging, VTC™ and VTEC®.
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