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Nissan RB30 DOHC Conversion Guide.pdf 371.2KB
16 downloadsA quick rundown:
Nissan did not produce this engine, but it refers to a turbocharged engine featuring an RB30E block with a twin-cam head conversion. Common hybrid in Australasia (referred to as the RB25/30 or RB26/30) using a RB30E bottom end mated to a RB25DE,RB25DET or RB26DETT cylinder head and turbo (RB20DE and DET heads are not used as the bores are different in size, RB30 86.0mm RB20 78.0mm, but were originally modified and used on the Tommy Kaira Rb30de as the RB25 engine did not exist). The RB25DE cylinder head from the A31 Cefiro C33 Laurel or R32 skyline (aka: Non VCT) can be used, and fits perfectly on (although better valve springs are recommended, GT-R valve springs are a decent upgrade). The RB25DET (from the R33 Skyline or C34 Laurel or Stagea) head is also used, however an external oil feed must be fabricated for the variable cam timing (VCT) on the RB25DET, and the galleries at the front of the engine do not line up. The variable cam timing may be disconnected altogether. Also it is wise to change the oil restrictors in the block to 1.5mm and get a full face oil pump drive collar machined onto the crank which solves it shattering at high RPM, with the use of a twin cam oil pump.
The fitment of a twin cam head from any of these engines onto a standard compression RB30E bottom end gives an ideal compression ratio for a mild to moderately modified street turbo engine around 8.2:1, (but always check your compression when building this engine as it may vary), making the conversion popular amongst those who would otherwise convert their RB30E to a high compression RB30ET using original ET bolt on externals.
Although it has a larger displacement than the RB26DETT, maximum possible horsepower is less, as the RB30 block lacks the RB26 block's internal cast-in bracing, and consequently cannot rev as high due to harmonic issues at ~7500 rpm. To compensate, the RB30DET produces more torque at lower revs due to its longer stroke. However they have been known to reach engine speeds up to 11,000 rpm with a lot of balancing and the use of the RB26 head with solid lifters. Power of the RB30det in this form can far exceed that of an RB26DETT, RB30DET's are usually only found in rwd cars as it's a lot easier to install, with the 4wd setup in the GTR or GTS4 an adapter plate has to be made to fit the 4wd sump as its bolt pattern is different to the RB30, as there is a adapter plate between the sump it sits off on the gearbox bolt holes, they will have to be modified to fit.
There is also an 'RB30DETT' kit manufactured by OS Giken of Japan, which bolts an extension on top of the RB26 engine block, and fits liners, to give an 86 mm bore x 86 mm stroke. It is available as an assembled short block, containing billet chrome-molybdenum crank, billet chrome-molybdenum H-beam connecting rods, forged pistons, and costs 1,500,000 yen.
In recent times, Rotorua Import Pro Shop (RIPS), a tuning garage located in Rotorua, New Zealand has emerged as one of the foremost tuners using the RB30DET engines, The vast majority of engines they do are RB30's. They have found that the stock Bottom end can easily withstand in excess of 600hp reliably, with many of their engines capable of running a Skyline in the 10 second range 0-400m sprint. RIPS also has produced the world's most powerful RB30, installed in a Nissan 240Z, this car has run 0-400m in 7.86 seconds at 177.4 MPH, running 1400hp+ using a stock unfilled block, stock crank, stock cradle, stock mains bolts, and stock wet sump without engine failure. That particular engine has now been installed into a purpose-built front engine dragster with a current best of 7.26 seconds and they are now going for 6 second 1/4 mile times at 200+ MPH. Another one of their developments is a 3.3 litre RB30DET dubbed the "RB33" by using a crankshaft with an extended stroke.
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