Project Nissan 350Z - Tech

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Project Nissan 350Z - Tech

Three years have passed since the last installment of Project Z and there's good reason. The car's been such a tank and so spectacular to drive, we found little reason to mess with it further. It almost cleared 100,000 miles of boosted abuse by various hard-driving editors-ranging from drift monkeys to the mechanically unsympathetic-and we were determined to squeeze every last mile we could out of it. We missed the mark by just 2500 miles, when the bottom end finally succumbed to excess blow-by and oil consumption.
However, we'd long anticipated the demise of our supercharged stock block. Arrangements had already been made for a newly built, low-compression, Jim Wolf twin-turbo engine package, assembled by Violent Racing Technologies-now called Verified Racing Technologies (VRT)-in El Cajon, California.
As much as we loved the predictability of the 330 wheel-hp delivered by the Vortech supercharger kit, we knew we would need to make more power in order to take on a Corvette Z06 in a shoot-out. While a low-compression engine, with the same supercharger running more boost, could easily have met the 500hp target we were shooting for, making low-end torque comparable to a small-block V8 would be an issue with the centrifugal supercharger, as it requires revs for boost. A pair of smaller turbos should spool quicker and provide more boost through the middle of the powerband.
To minimize downtime, we sent a spare VQ35DE long-block down to VRT to be torn down, machined and built with Pauter E-4340 connecting rods and JE 8.5:1 compression pistons. The plan was to drive Project Z to VRT on its last leg and have the built motor and Jim Wolf Technology (JWT) twin-turbo kit ready to drop in.
Things never work out as planned. On the big day, the car was just on the verge of spinning a bearing or two. I took the keys the night before, having been assured by its former driver that he checked the oil level regularly, even though the oil pressure warning light was already flashing intermittently when I fired the car up.
Figuring pressure was down because of blow-by degradation and the oil was just a little low, I stopped at the local gas station for some thick, el-cheapo stuff to last the 90-mile drive to VRT. Three trips to the cashier and four quarts later, I finally got enough into the motor to register on the dipstick, but the damage was already done. The faint rattle I heard earlier had developed into a full-on knock. Project Z only made it 10 miles down the freeway the next morning before the rod knock got so out of hand that we were at risk of damaging the original block (which we might re-use at a later date). The remaining 80 miles were made on the back of a tow truck at $5 a mile.
Modes Of Failure
Before building the new engine, we needed to figure out what happened to our original block, so the same mistakes wouldn't be repeated. As a starting point, the VQ is a tremendously stout engine, able to withstand endless beating under drift and race conditions. But we've seen and heard of two consistent signs of weakness from the people within Nissan Motorsports.
VQs and previous generations of Nissan motors, stretching from the QR to the RB series, all use a modern-style bearing material that's fairly intolerant to heat. While older engines used a tri-metal, lead-based alloy (designated F-770 internally by Nissan) that held up well at elevated temperatures, newer bearings use a lead-free material (for environmental reasons) that's far less tolerant of high oil temperatures. This is why most new Nissans from Sentras to Skylines all use oil coolers and bearing failure is so common for track-bound GT-Rs and 350Zs. At temperatures below 300 degrees F, where most synthetic oils are still stable, the newer lead-free bearing material has already changed chemically and been damaged permanently. Even at 250 degrees F, these bearings have lost significant load-bearing capacity.
Early generations of the VQ also used small bearings, which have less surface area to reduce friction and mass. The drawback is more load per bearing area. When coupled with a bearing material intolerant of high temperatures, that results in a lot of spun bearings in hard-driven cars. This is why we're seeing larger and larger bearing surfaces on updated versions of Nissan engines, as well as oil temperature sensors wired into the ECU. Add the fact that most new engines feature piston oil squirters, which transfer more heat from the pistons into the oil, and there's a snowball effect of hotter oil, bearing material transfer, increased oil clearances and reduced oil pressure.
Over-revving the stock VQ is also an issue. Newer engines use light pistons with small ring lands and low ring tension to decrease friction and reciprocating mass, and to clean up emissions. Under stock conditions, this shouldn't be a problem, but throw in boost, rich fuel mixtures and raised rev limits, and there's the potential for accelerated cylinder wear and eventual blow-by. The stock rev limiter was designed specifically so that piston speeds do not exceed 4100ft/second, based on the stock bore and stroke. Missed shifts or raised rev limiters could push the stock, low-tension, thin-strip rings beyond the margin of safety and either gouge the cylinder liner wall or cause ring flutter.
We saw the end result of both these issues in our VQ. The engine consumed and degraded oil at an excessive rate and it was the lack of proper lubrication that ultimately led to main and rod bearing failure. But, much to Nissan's credit, the engine steamed along like this for a good 30,000 miles. As long as we kept adding oil, the bearings kept going, although the blow-by and power loss kept getting worse.
Much of the burnt oil could be seen exiting the exhaust under boost or while the car was cold, so we had a suspicion that the stock rings and bore had taken a beating from being driven hard before reaching proper temperatures. And since the car was supercharged, boost only increased the blow-by effect-as well as the oil degradation-from fuel mixing with the oil that wasn't scraped away by the pistons or within the crankcase itself.
The Bottom End
Rarely do we have the opportunity to tear apart and completely rebuild an engine in our project cars, since the terms 'rebuilding engines' and 'cheap speed' never usually occur in the same sentence. It's a risky affair with a lot of potential pitfalls and expense if not done right. But in this case, building a high-performance bottom end able to withstand 500 wheel-hp is absolutely crucial.
The stock open-deck engine was designed to be light and strong enough only for the original 287bhp. Everything was designed from the ground up to save fuel, reduce weight and satisfy emissions regulations. In order to contain over twice the power, we would need much stronger internal components. Several options were open to us, but we decided to maintain the stock bore and stroke so we didn't have to deal with the limitations of increased piston speeds or gear ratios that didn't work for our power range.
We addressed compression ratio and piston strength with 8.5:1 compression forged aluminum pistons and rings from JE. The piston has been designed for forced induction, so it uses thicker rings (under more tension), as well as larger ring lands. The larger ring land (the area between the top of the piston and the first ring) adds significant resistance to damage from detonation. The stock piston uses a small ring land in order to reduce hydrocarbon emissions, as well as gain a couple of hp.
Since we're going to use forced induction, piston strength against detonation was far more important than squeezing out an extra couple of horses. In order to accommodate the larger rings and ring land, the oil scraper ring was moved down toward the free-floating wrist pin. In this case of this particular design, the oil ring groove partially intersects the pin bore, so a rail support ring is used below the oil rings and expander to support and prevent the rings from excess movement.
A dished-type piston changes compression and increases the volume of the combustion chamber. JE also machines in valve reliefs specific to the angles of the intake and exhaust valves, so its pistons are bank-specific (unlike stock). The valve reliefs are cut deeper for added lift and duration.
To take the extra bending load of higher cylinder pressures, the stock forged steel connecting rods were replaced with forged E-4340 chromoly crossbeam-style connecting rods from Pauter. Unlike the OEM I-beam rod, which is manufactured by using powdered metal forged together in a cost-saving process called sinter forging, Pauter uses a one-piece conventional forging process. This ensures continuous grain flow and starts with a billet piece of 4340 steel that is forged, shot peened for additional surface hardness, CNC machined and balanced to within a gram.
OEM-type rods also use snap caps, where the bottom half of the big end is intentionally broken off after being forged. While this offers more surface area to hold the rod cap onto the rod, it's done primarily to save time and machining costs. The Pauter rod uses caps that are cut off from the original one-piece rod forging and then bored to the proper journal diameter and fitted with pressed rod cap alignment sleeves to ensure an exact fit.
Pauter's crossbeam geometry is designed to increase bending strength in the direction of engine rotation and distribute the load over the whole, beefy cross-sectional area of the rod. It also has better windage properties than H-beam designs. We ordered our rods with the optional oiling channels on the journal end, which provide a path for oil to escape from the journal and make room for fresh oil to flow, while at the same time throwing the exiting oil toward the bottom of the pistons and wristpins.
The stock bearings were replaced with ACL tri-metal Race Series bearings that use a copper, lead and P76 overlay alloy, increasing load-carrying capacity as well as temperature tolerance. Lead helps the bearing's embedability (as well as prolong service life) without compromising wear on the crank or bearing itself. While it would have been a good time to lighten and knife-edge the stock forged and counterbalanced crankshaft, we left it alone to maintain street driveability and avoid issues with engine harmonics.
The Top End
While the engine was torn down, we also installed a set of Jim Wolf Technology 0.456-inch (11.6mm) lift, 261-degree duration (at 0.005 inches of lift) C2 intake and exhaust camshafts. These cams were specifically designed to work with the VQ's variable intake cam phasing system on forced induction applications to accommodate added airflow at mid and high revs while eliminating the excess duration and overlap of the stock NA cams.
The C series is intended for modified valvetrains, which use JWT harmonically matched valve springs (which allow for the minimum design spring pressure), while its S (or Street) profiles are engineered to work with stock valve springs. JWT also provided us with single-wound valve springs 30 percent stiffer than stock, with a higher natural frequency than dual springs, due to the larger wire diameter, which eliminates spring surge. Other valve springs can be as much as 80 percent stiffer than stock, which adds excess load and wear to the valvetrain, causing parasitic power loss.
JWT managed to use softer springs because its cams are designed, tested and ground to provide the desired flow characteristics, and accommodate the harmonics of the VQ valvetrain to eliminate miniscule profile changes. These changes are often overlooked by cam manufacturers and can induce spring surge, causing valve float at specific frequencies. Next time, we'll bolt on the turbos and install the engine, along with the additional hardware to keep Project Z running on the track. We'll see how close we come to the 500 wheel-hp needed for a fighting chance against the Z06.
Previous InstallmentsPart 1: August 2003Limited slip, flywheel, Nismo (Rays) wheels and tires
Part 2: April 2004Nismo wheel studs, BBS wheels, Hotchkis anti-roll bars
Part 3: November 2004Vortech supercharger
Part 4: Feburary 2005Nismo suspension

Photo Gallery: Project Nissan 350Z - Tech - Japanese Car - Sport Compact Car Magazine

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