Project Nissan Skyline R33 GT-R – Part 3: Borg Warner turbo and Full Race exhaust manifold

Let’s talk turbos. Okay, I have to admit something. Through the years I’ve literally run a dozen different turbos from four different turbo companies with my personal projects, but I’ve yet to run a Borg Warner. I can’t tell you how excited I am to finally be doing so. Having covered their turbos a couple of times at the PRI shows, and seeing how involved in the OE world (and Indycar, etc) they are, these turbos have always seemed uber-high end to me. I know my Project Supra’s engine builder, Jeff Gerner of Four Rings Performance will be satisfied. He’s always been about Borg Warner. Thanks to his Borg Warner S400SX3-boosted 1993 Audi S4, Jeff holds the Bonneville Salt Flats record for the “F Production Supercharged” class, where he reached a terminal speed of over 260 MPH—crazy for a 2.3L little engine. A tribute to his car is in Borg Warner’s own catalog, too.

Given my goals for the RB26, the 67mm Boost Lab turbo (essentially a Precision 6766) installed by the previous proved unnecessarily too big.  So what are my goals? First, I want a fun and reliable engine and so, therefore, I won’t be trying to squeak out every bit of power out of this thing. In order to keep the potentially detonation-inducing cylinder pressures at bay, I’m going to put a limit on the dyno-tested torque, as opposed to horsepower. With my 2.6-liters of displacement and 93 octane, I’m limiting torque to a very safe 350 lb-ft. Before you fret, read on because the power will be significantly higher. (By the way, notice this torque is not measured in “ft-lb” but “lb-ft” since we’re not turning a wrench).

Fortunately, this RB has a short stroke, and so RPM will be pushed to a healthy (and yet still stock!) 8000 RPM. This gracious engine speed means this RB will be able to make some horsepower, but as long as we can flow enough air to sustain torque. How much power? Well, contrary to popular belief, horsepower and torque are not mutually exclusive. They’re actually calculated from each other with the following formula: Horsepower = (Torque x RPM)/5252. So, by using our 8000 RPM and 350 lb-ft we can figure out our max horsepower potential.

By now, most of us already know that most aftermarket turbo torque curves are “bell-shaped” if boost is held at a steady PSI. This also assumes we’re talking about a turbo performing in its intended power level (otherwise, a large turbo at very low boost will have a flatter curve at high RPM). After the torque hits its peak, it significantly starts to drop, thereby keeping the horsepower relatively flat (and sometimes even dropping on the smaller ones) thereafter, given the aforementioned formula. Therefore, on an average performance car that redline to around 6500 RPM, if we’d see some peak torque number—let’s say it’s 350 lb-ft—in the midrange, the horsepower would end up being somewhere between 335-400 WHP at peak, and typically before this redline. However, given the RB26’s rev limit, our AEM Infinity EMS, and a very knowledgeable tuner like Chad Charlton at Modified by KC, we can cheat! Let me explain.

What if we could get Chad to get a turbo to whip up the 350 lb-ft of torque pretty early in the midrange, but then also keep that torque fairly flat through redline?  The top-end would be like that of a centrifugal supercharger, which–because of the belt-driven design–has an incremental boost increase that doesn’t do much for the midrange but screams by redline. It kind of feels like you’re angrily chucking 3-4 ex-girlfriends out the window with every incremental 1000 RPM (please don’t take this literally). This incremental boost is what keeps these torque curves flat, keeping, therefore, the horsepower climbing at around a 45-degree angle thru redline. So how do we do that? Thanks to the AEM EMS, we can tune the turbo to hit the desired range (whatever boost the 350 lb-ft requires, within reason) and then slowly feed the engine more boost through redline. As long as we keep torque the same, we won’t be hurting anything, but we’d need a turbo that is both quick spooling and also high flowing. How can we have it both ways? Enter the Borg-Warner 8374!

I like the fact that—while being known as a quick spooling turbo—the Borg-Warner 8374 is rated to over 700 WHP because this not only means lower PSI numbers to achieve our goals, but it also leaves room to pursue higher power numbers in the future, should the need arise. In the end, we’ll have the best of three worlds: turbo torque, a good top end, and reliability not just for the engine but also for the drivetrain components (by achieving this power at a lesser torque). Hey, if you have money to throw at things as they break, have at it–make 500+ lb-ft of torque with the 8374. I have a stock RB, however (and I’m married–enough said).