KNOW THE LEDGE WITH NISSAN’S MOST POPULAR FOUR-CYLINDER
When it comes to Japanese sport compacts, an engine’s success stems from its design, performance, consumer embrace, and, in our world, aftermarket support. For Nissan fanatics, the venerable SR20 engine is a four-cylinder favorite. This versatile mill was produced for over 13 years in practically every configuration imaginable; from naturally aspirated and forced-induction, to all three driveline options: front-wheel, rear-wheel, and all-wheel drive. This engine family propelled 18 different Nissan/infiniti platforms throughout the world. Of these, America only saw the Sentra, Pulsar NX and Infiniti G20, which were all FWD, naturally aspirated SR20DE (Sr-engine series/20-2.0 liters/d-dual Overhead Cams, E-electronic Fuel Injection) engines.
SLIDING INTO THE SPOTLIGHT
At a time when drifting matured from an underground and illicit style of driving in Japan to a mainstream form of motorsport in the U.S., American enthusiasts had a modest selection of Japanese platforms (Supra, 300ZX, 350Z, RX7, MR2, 240SX, AE86) to choose from. Of these choices, the 240SX offered an affordable, plentiful, lightweight, and balanced RWD chassis. The USDM 240SX came equipped with a naturally aspirated single-cam KA24E or dual-cam KA24DE, engines that did not benefit from as much support from the aftermarket at the time. Fortunately, since the 240SX is the same as the JDM Silvia and 180SX, a complete RWD SR20DET engine, transmission, wiring harness, and ECU could be swapped with relative ease. Add to this the extensive aftermarket support already offered by Japanese tuners and performance-minded manufacturers, and the performance ceiling rises substantially.
THE BOOSTED VARIETY
The SR engine family comes in a variety of displacements and cylinder head technologies. The performance-oriented, RWD SR20DET (yes, the “T” stands for turbocharger) engines didn’t gain a foothold stateside until drifting became popular in the early 2000s. These engines, the three variants that powered the JDM S13, S14, and S15 Silvias and the 180SX, are the most common swaps. So, what’s the big deal about these engines? They’re factory turbocharged, have power potential twice that of stock output with factory internals and, thanks to the aftermarket, can be built for even greater power potential.
Nissan engineered its turbocharged, all-aluminum SR20DET engine with a square, 86mm bore and 86mm stroke dimension, which is favored for its balance of torque and horsepower output. The block features a closed deck with alloy cylinder liners and each cylinder has an oil squirter to help maintain piston temperatures. Up top, the 16-valve cylinder head features chain-driven, dual overhead camshafts that permit independent adjustment of camshaft timing (when aftermarket adjustable cam gears are installed). The cams lift the valvetrain by way of rocker arms with hydraulic valve lifters, the benefit of which is reduced maintenance, since they constantly and automatically adjust for valve clearance. A single throttle body regulates the incoming air charge that pressurizes the aluminum intake manifold. As the air is distributed to the intake ports, side feed, high-impedance fuel injectors spray atomized fuel into the combustion chambers. A coil-on-plug ignition system delivers precise spark timing for optimal combustion and performance. Over the course of its production life, the SR20 experienced an evolution of small changes that distinguish each generation Nissan released.
THE RWD VARIANTS
The early SR20DET engines were commonly identified by their valve cover. The “Red Top” and “Black Top” (these were sometimes referred to as “Flat Top” as well) engines were found in the RPS13 180SX and S13 Silvia. These engines came with a “High Port” cylinder head that relied on non-variable timing camshafts and offered excellent airflow from the factory, making them desirable as a performance option that did not require heavy port work. They use 370cc/min fuel injectors to deliver fuel and a Garrett T25G journal bearing turbocharger for boost pressure. This engine produced 200 horsepower in stock trim but could support approximately 400 hp safely on a stock bottom end, the right combination of bolt-on parts, turbo upgrade, fuel delivery improvements, and calibration.
Later, Nissan released an updated SR20DET engine with Valve Timing Control (VTC), which is Nissan’s variable valve timing system. This engine first appeared in the S14 Silvia at the end of 1993. This engine, characterized by its unusually shaped valve cover, earned it the nicknames “Notch Top” and “Slant Top.” This new cylinder head, known as the “Low Port,” features a redesigned intake manifold feeding slightly smaller ports for
increased intake velocity. Calibrated with the VTC on the intake camshaft, the low port head offered improved response while delivering greater peak power compared to the previous SR20 engines. With boost supplied by a larger, journal bearing Garrett T28 turbocharger, stock output increased to 217 hp. In 1994, Nissan Motorsports released a limited edition called the 270R. This run of only 30 units generated 270 hp and sported a host of Nissan Motorsports performance upgrades to complement the higher engine output.
In 1999, Nissan unveiled the last S-chassis to be powered by an SR20DET engine, the S15 Silvia. The SR20DET that powered the S15 Spec R continued to benefit from the VTC cylinder head and came equipped with a Garrett GT28R ball bearing turbocharger and larger, 480cc/min injectors. For this engine, Nissan eliminated the “dumb” coils with the external ignitor in favor of “smart” coils with built in igniters. An improved engine management system regulates the fuel delivery and ignition timing to produce 247 hp.
PARTS, POTENTIAL, POWER
What gives the SR20 such potential and staying power? Aftermarket support. Nissan started producing this engine in 1989 and despite ceasing production of this engine with the model year 2002 S15 Silvia Spec R, the aftermarket continued to support each of these variants with performance parts that have continued to release even to this day. From the basic boltons to rotating assemblies, stroker kits and full cylinder head tuning, options for modification are plentiful.
The bolt-on friendly SR20DET engine welcomes most modifications with increased output in return. After you’ve made the basic intake, downpipe, and exhaust upgrades, prepare to invest in engine management solutions for the more advanced bolt-ons like intake manifolds and front-mount intercoolers. The importance of an aftermarket engine management system becomes paramount once you’ve upgraded injectors, fuel pump, ignition system, exhaust manifold, and turbocharger, followed by an increase in boost pressure. If you’ve taken the valve cover off to upgrade the camshafts, it’s a good idea to add rocker arm stoppers to keep the rocker arms from being flung at high engine speeds. If you’re hardcore, ditch the hydraulic valve lifters in favor of solid lifters. Since solid lifters do not move, they reduce the chances of the rocker arms being flung from their positions. The only caveat is that they’re a pain when it comes to dialing in the valve lash. Even so, many argue that the effort is worthwhile, since they won’t likely need to be adjusted for quite some time. Depending on the parts you choose and the type of fuel you’re running, these upgrades could get you anywhere from the high 200-to-mid-300hp range.
If you blew your SR20 engine or are just ready to step up to the next level, you’re ready to upgrade your engine internals. The alloy cylinder liners of the SR20 can only be overbored 0.5mm or 20,000ths of an inch twice (86.5 mm and 87 mm) before the liner walls are too thin and you are forced to resleeve the block. Fortunately, there are a few choices available when it comes to resleeving a block, and the stout, aftermarket ductile iron cylinder sleeves expand your options to use much larger pistons. In the case of the SR20, you can safely go up to a 90mm bore and still have plenty of cylinder wall thickness to contain the immense cylinder pressures without cracking. It’s also a good idea to upgrade connecting rods at this time, especially if you’re planning to increase the output of the engine. For increased torque, lengthen the stroke by way of a stroker crankshaft. Plan to order custom pistons if you do, as the wristpin position will need to be adjusted to accommodate the longer stroke.
WHAT’S IN YOUR HEAD?
Once you’re done strengthening the rotating assembly and/ or increasing the displacement of your SR20 block, it’s time to improve the volumetric efficiency of your engine. To improve airflow in and out of the cylinders, simply installing higher lift and longer duration camshafts can have a significant effect on engine output and the shape of the horsepower and torque curves. Larger valves and port work can further complement the bigger camshafts for optimal volumetric efficiency. But remember, bigger isn’t always better. Head porting, valvetrain and camshaft selection go together with turbo sizing to achieve the desired peak output and torque curve. Going big with high peak power output is great if you’re drag racing, but usually
translates into numb response and boost lag on the streets or on a road course. Choose your upgrades based on the purpose for the build or what you plan to do most with the car. A high output build typically sucks in traffic. Horsepower junkies will argue against the SR20DET engine, since it is not based on an iron block or that its output can’t compete with the likes of the inline six-cylinder RB or JZ engines. However, there are compelling reasons to get into an SR20 swap. The lightweight, aluminum SR20 engine helps to maintain the excellent weight balance that the 240SX is known for, which contributes to its desirable, neutral handling. The RB and JZ engines weight quite a bit more, which puts more ballast toward the front. The SR20’S relative attainability is also an attractive talking point, with engine importers on either coast selling complete swaps for anywhere between $2,800 and $4,000. Thanks to more than two decades of development and aftermarket support, there are still plenty of parts available for these engines. When built properly, the SR20 can reliably support more than 700 hp at the wheels. For those seeking a reliable, cost-effective engine swap that is practically a drop in for the S13 and S14 240SX, look no further.
››The Flat Top cylinder head features fixed cam timing. However, the aftermarket offers adjustable gears that permit “degreeing” the camshafts for optimal performance.
››The first generation Flat Top cylinder head (1) can be distinguished from the second generation (2) by the cooling fins at the front of the head. The Notch Top (3) had the VTC cam gear that protrudes from the front.
››The Flat Top cylinder head (A) features a cast in, “high angle” intake port. By comparison, the Notch Top (B) features a more traditional looking low port design.
››The distinct shape of the Notch Top valve cover houses the VTC cam gear that adjusts the intake cam timing.
››The sheet metal rocker arm stoppers that bolt onto the cam caps help to keep the rocker arms from being flung from their positions under the cam lobes at high engine speeds.