Project Serious Sentra

Freshening the SR20DE-T

Text & Photos By Evan Griffey

[Put into HTML format by Dan Thompson]

This article originally appeared in the Turbo & Hi-Tech Performance October 1997 issue and was reprinted with permission. For more info on Turbo Magazine check out their website.

The white Mustang GT had shown the classic signs of confrontation, but nothing had come of it. Leaving a light on PCH, all was normal. Once up to fifth-gear speed, it happened, the Ford came whizzing by accompanied by the whine of supercharged power. A quick downshift to fourth, not enough power, into third and the turbo started singing as the tires lit up. The Sentra worked its way through the gears, reeling in the Mustang like a Sea Bass after a long battle at the end of a hook-laden line. Near the top of fourth there was a light rattle-like ticking being made from the engine, but we were in hot pursuit. The Sentra swept by the Ford and accelerated until the speedo was pegged. After missing our street and making a U-turn, we passed the 'Stang going the opposite way, its pilot held his head low in shock and embarrassment. The ticking in the SR20DE engine had been a recurring one and since nothing had ever happened, it was believed the engine could handle a little detonation. Weeks later, the engine began to smoke and a compression check turned up a bad cylinder. While cylinder one, two and four registered 150 psi, number three could only muster 50. The lesson here is there is no "handling" detonation, any is bad and turning down the wick a couple psi would have avoided the whole scenario.

Luckily for us, these turbo-spec pistons from Nissan Motorsports were ready to go. When used in accordance with a Nismo metal head gasket this is the best method of lowering compression. Using a thicker head gasket is less expensive and viable for most lower boost applications.

Dan Benson of Benson's Automotive Meta-Lax stress relieved the rods and pistons. The Meta-Lax process involves finding the part's resonance frequency and shaking the table at a lower frequency which lowers the resonance frequency and relieves stress.

Here we see a shot-peened and deburred rod compared to an untreated unit. The SR20DE rods are quite stout. They feature thick I beams, a lot of material around the ends and beefy rod bolts.

Luckily we had a set of Nismo SR20DET pistons and rings and a Nismo had gasket waiting in the wings. This would be an excellent opportunity to upgrade the internals. Our pistons and a set of extra rods were delivered to Benson's Automotive. We discovered that ordering rod bearings is no easy chore as Nissan stocks five or six varieties. A particular application is determined by a five digit number on the crankshaft's forward-most counterweight. The Sentra was delivered to XS Engineering in Fullerton, California for the in-engine piston swap. Eric Hsu and Peter "Fae-lo" Yeung managed to find the number (22221) and the correct bearings were ordered. We considered upgrading the rods but the stock SR20DE units were quite stout so Benson's Automotive resized the inside diameter of the big end, deburred and deflashed the beams by grinding off the casting flashes and shot-peened all the rods to relieve stress risers. Benson's also balanced the assemblies, taking a whopping eight ounces out of one rod. Then the rods and pistons were stress relieved on Benson's Meta-Lax shaker table. The Meta-Lax process involves finding a component's resonance frequency, shaking the table at a lower frequency and reestablishing a resonance frequency which should be lower at this point. The components are then treated again at an even lower frequency. The initial treatment lasts 30 minutes. The secondary treatments, which try to lower the resonance frequency further, are 15-minute sessions. The resonance frequency can be looked at as stored stress in a part. Lowering this frequency lowers the amount of stress in the component which enhances its durability. For a more complete look at the Meta-Lax process refer back to the May 1995 issue.

With the rods and pistons shaken, not stirred, XS Engineering put the SR20DE back together. While the car was down, we had the valve cover and intercooler piping powdercoated white by P.S.C. A more extensive look at engine detailing will appear in a future installment. Once back on the road, the engine still smoked but we thought it would subside once the rings seated. But the condition persisted, the car ran hot - 232 degrees and a lifter started clicking. We believe this was due to oil starvation. The culprit was a failing turbo. This surprised us as we religiously used a turbo timer to cool the engine oil at shut down. Upon disassembly at Turbonetics, technicians found the shaft was damaged beyond repair, the bearings were shot and the wheels were unusable. So a new center section cartridge was built and installed. A T28 turbine wheel was put in the machined .86 A/R T25 turbine housing and a Super-60 compressor wheel was put in the T3 compressor housing. The Super-60 wheel is eight percent larger than the biggest Garrett T3 wheel. Turbonetic's Rick Head estimated the turbo's flow to be 450 cfm at full boost (16 psi) with a total output potential checking in at a conservatively estimated 300 horsepower. Rick offered this turbo tip of the month; a new oil feed line should be part of any turbo rebuild. Hot oil can layer in the line and restrict the passage which reduces the amount of lubrication for the turbo and substantially shortens its life. We cannot be sure this scenario is what happened to Project SE-Rious Sentra but it is excellent advice for any force-fed engine.

With the Sentra back on the highway, we will address the clicking lifter and possibly retune the car and take advantage of the more efficient front-mount intercooler. Stay tuned.