The Nissan VG30DETT

Designed in the late 1980s, Nissan's twin turbo, DOHC, 4-valves per cylinder powerhouse is one of the all-time classic turbo engines. Surprisingly sophisticated both for its time and cost, the engine was fitted to the 300ZX twin turbo sports car. Nissan engineers were aiming very high with the car - the background to the engine development makes this very clear.
In this article we'll cover the technical nitty gritty of the engine and its original development goals.
The Basic Anatomy
The VG30DETT is 2960cc in capacity, with an over-square bore/stroke relationship of 87 and 83mm, respectively. The combustion chambers are of a pent-roof design, with the spark plugs positioned close to the bore centre. The four valves per cylinder are operated by double-overhead cams working with zero-lash hydraulic tappets. The compression ratio of this twin turbo engine is 8.5:1 and the original specs show an SAE NET output of 300hp at 6400 rpm and a peak torque output (again SAE NET) of 283 ft-lb at 3600 rpm. Almost a cube in physical dimensions, the engine is 710mm long, 775mm wide and 695mm high.
While based on the much lower-powered VG30DE engine, major changes were made for the twin turbo engine. These weren't just limited to strengthening the engine and installing the twin turbos; instead the opportunity was used to design completely new intake and exhaust systems. The engineers made much of the fact that twin intercoolers, twin throttles, twin plenum chambers, twin turbos, twin exhausts, twin catalytic converters and twin mufflers were adopted.
Intake System
The intake system design had to balance two opposing outcomes: the smaller that the intake runner diameters were made, the greater the frictional losses (and so pressure drops) but the larger the intake runner diameters, the slower the airflow speed, resulting in a decrease in cylinder filling, especially at low rpm
In addition, simulation and testing showed that long intake runners resulted in better torque development at low engine revs - however, fitting long runners into an already crowded engine bay was going to be difficult. Runners that were 360mm long gave peak intake efficiency at 4400 rpm, while lengthening these to 480mm dropped the peak intake efficiency revs to 3600 rpm. Since one of the goals of the engineers was strong bottom-end torque, the longer runners became a requirement. Further testing showed that a runner diameter of 48mm worked well with the 480mm long design.
It's interesting to note the major amount of development that occurred in tuning the intake system in this turbocharged engine. Many turbo engines - including Nissan's own RB26DETT Skyline GT-R engine - have no intake resonance tuning at all.

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