SE-Rious Sentra Part V
Fuel Enrichment Tech
Text & Photos By Evan Griffey
[Put into HTML format by Dan Thompson]
This article originally appeared in the Turbo & Hi-Tech Performance October 1996 issue and was reprinted with permission. For more info on Turbo Magazine check out their website.
When we last left project Sentra we had just installed the new T28 turbocharger from Turbonetics and were turning our focus on fuel enrichment. To refresh your memory our fuel system was maxed out on many fronts. The 370cc Q45 injectors, the stock mass air sensor and Bosch fuel pump were all operating on the limiter. However, even with the boost backed down to 12 psi (from 15 psi) the car felt much more eager to get down to business than with the T25.
Prior to upgrading the fuel system, the Sentra was strapped to Dynamic Autosports' DynoJet dyno where it generated 245 horsepower at the wheels. From there we began construction of our custom fuel rail with a 300ZX twin-turbo fuel pump, as well as stainless-steel tubing and auxiliary fittings supplied by MSD. The rail was mocked up by Belanger's Muffler on a spare manifold and finalized by Jim Wolf Technology (JWT). The injectors are also MSD units rated at 50 lb/hr, which is equivalent to 530cc. (To convert from lb/hr to cc, multiply the lb/hr figure by 10.6.) The top-feed-style MSD injectors fit snugly against the manifold's O-rings, making this kind of upgrade a very easy and cost-effective method considering the price of many aftermarket side-feed injectors. The best-case scenario (and the most expensive) would have been the 444cc injectors from a limited-edition Nismo 270R Silvia, as they would have featured a R&R [Remove & Replace] installation on the factory rail. The 444cc "upgrade" injector for the 300ZX would have required some alteration to work, as the outside body is bigger than the stock SE-R and Q45 injector. A 444cc Skyline or Pulsar GTi-R injector is a low-impedance unit and would not work on our application. The MSD injectors are six-hole squirters which should enhance fuel atomization and help idle quality. The stock mass air sensor was swapped for a 70mm Hitachi unit.
Another area of power generation that had to be severely challenged in the SR20DE's forced-induction environment was the ignition system. Kudos to Nissan, we have experienced no misfires or shortcomings from the stock system. However, with the power figures we would be dealing with, we thought it prudent to upgrade. A Crane HI-6 capacitive discharge ignition and PS-92 coil now spark a fresh set of factory plug wires.
With the new fuel system and ignition up to speed, it was time for JWT's Jim Wolf and Clark Steppler to tune in the power. This is accomplished by bypassing the stock computer's ROM (Read Only Memory) and using a custom-programmed JWT chip that operates off a daughter board in the ECU. With this setup, Jim Wolf Technology says the Hitachi mass air sensor has another 100 horsepower left in it while the injectors are operating at 75-percent duty cycle.
During the tuning process, Clark noticed that the inlet temperatures were quite high - 175 degrees when running at WOT for extended periods of time. This caused detonation at 18.5 psi of boost pressure. The car was also sensitive to ambient temperatures, running better in the morning and late at night than during mid-day. It was decided to cut back to 1.1 bar where there was no detonation and fine-tune up to this level. We are currently configuring a front-mount intercooler setup and should be able to turn the wick up with more efficient cooling. JWT also reports that 18.5 to 20 psi may be the most we can expect out of the turbo as the turbine side is creating 42 psi of backpressure at these levels. The only foreseeable options are a different, nine-blade wheel, a bigger, rare 1.04 A/R T25 housing or moving up to a T3 housing.
With the T25 programming and the boost turned down a bit, the car was still capable of providing whiplash-inducing torque. Turbo response was also excellent as the Serious Sentra was able to quickly carve its way through commuter traffic. The Z-car fuel pump plain killed driveability as throttle response was sluggish at best - we were surprised how noticeable the difference was. Once again the value of proper tuning became apparent. After getting the car back from Jim and Clark the sluggishness was gone and the responsiveness was back. However, the neck-snapping brute force had been replaced with a smoother more linear power delivery. According to our Blitz boost gauge, the T28 is generating 1.1kg/cm2 or 16 psi of maximum manifold pressure when the T-BAC is at its highest setting. On Dynamic Autosports' DynoJet dyno the SR20DE pumped out 260.7 horsepower and 264.7 lbs-ft of boost at the wheels of the Serious Sentra.
We also updated the rolling stock on the SE-R from 15 inches to 16 inches. The wheels are 16x7 Spa Inter Mesh alloys from GBC Motorsports. The ground-breaking news surrounding the Inter Mesh's is that GBC Motorsports has convinced the manufacturer to supply 4-on-100mm bolt pattern wheels to cover the popular sub-compact cars like the Sentra, Hondas, Acuras and other imports. We were pleasantly surprised by the Spa wheels as they looked much better in person than they did in the PR photos we'd seen. They looked better still when mounted on the car, giving the SE-R a much more Japanese look. The wheels were shod with 205/40-16 Nitto NT-505 rubber. Not only does the new combo look great, torque steer, a real problem, was noticeably reduced. Grip from the 180-treadwear rated Nittos was significantly greater than the 220-rated tires they replaced. We were able to get much better launches on the street and when max boost hits the car seems to float less than before.
Under the banner of troubleshooting, we have been struggling with a leaking transmission. Dynamic Autosports Power Technician Dan Sherman went through the five-speed gearbox, installed new seals, throw-out bearings and a new speedo cable. We discovered the previously installed metallic clutch disc had damaged our flywheel so it was resurfaced. Next Dan installed Dynamic's six-puck Kevlar Double-D clutch and then bolted on a new transmission case. The leakage has stopped and the clutch feels stout, but there may still be some gremlins in the tranny.
Our plans for now may include a return trip to Jim Wolf Technology for a high-octane program, going front-mount on the intercooler, addressing the suspension and interior, as well as slapping on some slicks and getting to a quarter-mile strip.