The Nissan VQ37VHR is a notoriously difficult engine to modify in naturally aspirated form. This is due to its VVEL continual variable cam timing system on the intake side of the engine that can infinitely adjust both the intake valve lift and duration. The VVEL system does not use a camshaft, but instead uses complex combination of parts including a rocker arm and reciprocating followers that open the intake valves by transferring the rotational movement of an eccentric cam to an output shaft. The movement of the output cam is varied by rotating a control shaft with a DC stepper motor that changes the fulcrum of the links that move the followers. This makes the continuous adjustment of the amount of the valve’s lift and duration of opening relative to the crankshaft’s rotation during the intake valve event in the four-stroke cycle possible. Because of the lack of an intake camshaft, this engine cannot be modified in the conventional sense when it comes to controlling the valvetrain. To top it off, Nissan says these parts are not serviceable. We will be taking that statement as a challenge and will be building this engine with help of some of the best Nissan minds in the industry. Enter Z1 Motorsports and Jim Wolf Technology.
Many high power VHR engines have been built, but they have mostly been forced induction builds due to the difficulty in working with the complex VVEL system. We are going to do things the hard way and will try to reach the maximum of the VVEL system naturally aspirated. Below is a video we did a long time ago showing how the VVEL system works showing just how complicated the system is. Complicated or not, we will be building an engine that can take full advantage of everything the VVEL system can offer which is potentially a good producer of low end torque in addition to being able to rev freely.
We are building an engine that has the potential for high revs and high revs increase the tensile stress on the rod. Tensile stress is harder to contain than something like turbo boost which adds compressive stress. Tensile stress wants to pull the rod apart vs tensile which wants to squish it together. Tensile stress is what breaks things first. Usually at the rods weakest point, the rod bolts. To deal with this, we replaced the OEM Nissan rods with some K1 Technologies Connecting rods, part number 033CW17150.
Each K1 connecting rod is CNC machined from a 4340 steel forging and then undergoes a core hardening and shotpeening processes to improve its fatigue strength. In addition, every K1 connecting rod is magnetic particle inspected (MPI). During this inspection process the connecting rod is magnetized and then a magnetic flux, such as iron particles, is applied to its surface. Any surface irregularities will cause a disruption in the magnetic field, which the magnetic flux is attracted to. This attraction helps reveal any surface imperfections or flaws on the connecting rod’s surface.
A connecting rod experiences a high amount of compressive and inertial loads, which distorts and ovalizes the connecting rod’s big end bore. This distortion and ovalization causes the connecting rod bolt to undergo bending, tensile, and sheer stresses. Making the connecting rod bolt among the most highly stressed fasteners in an engine. Due to the high levels of stress, K1 connecting rods are equipped with ARP 2000 connecting rod bolts for their high tensile strength and excellent notch toughness. Notch toughness is a material’s ability to resist loads and absorb energy in the presence of a surface imperfection such as a crack or the circumferential, V-shaped notch of a bolt’s threads. To further increase the rods and bolts fatigue strength we had them WPC treated.