'94-'99 The Low Port
In an effort to reduce emissions, Nissan shortened the SR20DE's intake port and placed the injectors closer to the intake valves by using a more conventional intake port design. This intake port makes a sharp turn inside the head and doesn't flow quite as well when ported. Although, it flows nearly as well as the high port when stock. Due to the lower un-split port configuration, the hydraulic lash adjuster also intrudes on the roof of the port. The low-port engine has milder camshafts especially on the intake cam, which is about 10 degrees less duration than the high port. The intake manifold most easily identifies the low-port motor with the plenum on top of the runners. In stock and modified form, once the cams are changed, the low port more than equals the power of the high port, usually producing more bottom end torque and the same amount of horsepower.
'00-'01 The Roller Motor
The '00 SR20DE had significant changes to improve emissions and help power and response. The main cap girdle was deleted to reduce windage losses sacrificed by having the girdle so close to the rotating crank assembly. The pistons were lightened with a slipper skirt racing-inspired design and are coated with black Teflon-looking coating to reduce friction. The pistons have thinner, lower tension for less friction rings. The top ring is moved higher on the piston to improve emissions.
Although the connecting rods are unchanged, the crank is considerably lightened. Since the pistons are much lighter, Nissan was able to remove one counterweight from the crank. The bearing journals are micro-polished. The most noticeable external feature of the motor is the new, taller valve cover to clear new friction-reducing roller rockers. The head has valves with a 3mm shorter stem with springs and retainers to accommodate this shorter height. The roller SR has a revised intake manifold with shorter runners. The intake has a larger diameter, smoother pipe between the throttle body and a new larger airflow meter. The exhaust manifold has a close-coupled catalytic converter. The roller SR has 145 hp.
For our buildup we're starting with a JDM Bluebird (the JDM version of our U13 Altima) high-port SR20DE. This engine is very common in JDM engine salvage yards and can be found for as little as $275 for a clean unit. We plan on installing this motor when it's done in our daily driver 200SX SE-R. The engines are so cheap that we decided to do our build leisurely on this spare motor while we continued to drive our 200 on the stock low-port motor. The tricks that we apply to our built motor will also apply to all versions of the SR-so no matter what year you have, you'll get similar results.
Machining and headwork are two of the most expensive parts of a new motor build and we'll save a lot of money here. Since our car sees plenty of track days we'll work to address the SR's weaknesses. Not all of these have to be done on a street car and we'll tell you where you can skip a step to save some money.
To get a good gain of power across the board, we decided to up the compression ratio of our motor to 11.5:1. To do this we obtained a set of SR16VE pistons from GSpec. The SR16 VE pistons are used in a 1,600cc JDM variant of the SR20. These pistons are a high-quality cast OEM piston. It features hard anodizing in the ring grooves for better ring seal over a long period of time and anti-friction coating on the skirts. The pistons use the thinner low-tension rings from the '00-'02 SR. This reduces friction and improves ring seal at high rpm. The pistons are also about 40 grams lighter than the stock pistons. At about $160 a set, they cost less than half of what a set of forged aftermarket pistons go for. While not as tough as forged pistons, they're easier on the cylinder walls, can run a much tighter pistonto- wall clearance for better ring seal, have less oil consumption and, for street use, have a longer service life.