SR20 EX­PLAINED

KNOW THE LEDGE WITH NIS­SAN’S MOST POP­U­LAR FOUR-CYLIN­DER

Super Street - - Contents - WORDS & PHO­TOS Richard Fong

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.

SR20DET BA­SICS

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.

REC­OM­MENDED UP­GRADES

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.

AD­VANCED EN­HANCE­MENTS

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.

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