Note :-  Information contained in this web site has been published in the public domain to freely help like minded  people. My Text and pictures are not to be reproduced in any form without my consent and certainly must not be distributed for profit ! I didn't think I needed to spell this out but apparently I do......................... Any sites that have copied my pictures should at the very least include a link back here or other acknowledgement or remove them ! Nissan RB30 Twin Cam Head Conversion This conversion was achieved using a "naturally aspirated RB25 twin cam head without variable valve timing". This allowed the use of a standard original Nissan RB30 head gasket and no modifications to the cylinder head coolant galleries were required. A genuine Nissan head gasket was used upon assembly. The original RB25 normally aspirated valve springs were quite soft at 39 Lb. which limited performance. A set of GTR springs were fitted to suit the turbo application.

Pick an RB25 engine that has a removable rubber grommet in the centre of the crank angle sensor. This denotes a crank angle sensor that can be disassembled to allow replacement of the trigger disk. This feature may be required if you plan to use a programmable ECU. Of course, I picked the wrong bloody engine didn't I, so it cost me another $150 for a crank angle sensor from an RB20 that 'could' be disassembled.

Photo used with permission

This shows the crank angle sensor that can't be disassembled easily. You can see the collar that was pressed down holding the disc in place - there was a bearing on top of that. There is no easy was of holding the collar or getting leverage under it without damaging the disc or collar.

Photo used with permission

This is the unit that can be disassemabled easily. Instead of the collar, there are a couple of screws clamping the disc in place. Use a big hammer to punch out the pin (circled in photo) that holds the drive adaptor onto the shaft, then press the bearing off to gain access to the screws that clamp the rest of the shaft onto the trigger disc.

While the lid was off, I threw in a set of  ' Custom ' Wiseco forged slugs in anticipation of things to come. These engines are amazing - This block has done over 400,000 Kms and still has hone marks, the bores are round and the bearing clearances were still within factory spec ! The compression ratio was set at 8.5:1 as I didn't want to sacrifice off boost drivability.

This photo shows the tensioner mounting stud in it's new location. The cam belt idler pulley from the RB25 engine is required which simply bolts into place on the RB30 block just below the water pump. The RB25 cam belt is too short because of the increased deck height of the RB30 block. The RB30 cam belt tensioner cannot be used in its original location because belt tension cannot be gained using the Dayco 94407 belt. As I could not find a belt a few teeth shorter, the tensioner was moved to a new position above the water pump to waste a small amount of belt length.

To find the length required for the new cam belt, I cut the original RB25 belt (141 teeth long) and ran it around the pulleys, idler and tensioner( in a slightly slack position so that tension can be gained ) so that it started and finished on the inlet cam pulley and taped it in place. Then I counted the number of teeth left between the ends of the cut belt. The new belt needed to be 11 teeth longer at 152 teeth.

The belt manufacturer Dayco was the only manufacturer that I could find that included the number of teeth in its timing belt catalogue listings. The belt with the required number of teeth is the Dayco 94407 at 152 teeth. A VL turbo oil pump was used.

Grit blasting does a fabulous job of cleaning up the inlet manifold and  exhaust manifold heat shield. If you decide to clean up the inlet manifold by grit blasting then make damn sure that it is sealed up very well to prevent  the grit from lodging inside where it can't be cleaned properly. Any grit that goes through an engine will stop it real quick ! A few cans of clear lacquer will keep it all looking good. Don't bother polishing the manifold unless you are extremely keen - it's far too hard ! I bought a naturally aspirated engine instead of turbo because it was way cheaper. I picked up a turbo exhaust manifold quite cheap too. I fitted a deflector plate to the inlet manifold to disperse the charge air so that pots 3 and 4 don't get pressurised more than the other cylinders. A 4" slot was milled in the underside of the manifold between the throttle body and the start of the runners. An aluminium plate was welded in. If you look through the throttle body, the top of the plate comes up to about the height of the butterfly.

An RB20 turbo exhaust manifold can be used as this will bolt straight on. If you're keen, then you can make an extractor style manifold from steam pipe. A steam pipe elbow was welded to the top of the exhaust manifold so that a Turbonetics wastegate could be fitted. An RB30 exhaust manifold won't fit as most of the flanges are angled the wrong way. Here is the flange orientation on both heads... 1  2  3  4  5  6 /   /   /   /   /   \    RB30 \   \   \   \   /   /    RB25

Here the old turbo was bolted on so that I could set up its plumbing and check clearance in the car. The first dyno run proved that a bigger turbo was needed so a TO4E was fitted.

The RB30 lower timing belt cover can be used. Obviously, the RB25 upper belt cover needs to be used but it needs to lengthened a bit due to the increased deck height of the RB30 Block. To work out the dimensions of the extension, I made a cardboard template ( a couple of them actually ). I then made an extension out of aluminium, painted it black and riveted it onto the upper timing belt cover.

Here the new engine is lowered into place for a trial fit to check clearance around the turbo and inlet manifold before going off to the engine dyno.  An Autronic SMC ECU provides multiple ignition outputs to operate the DFI. It drives 3 Bosch ignition modules which drive 6 EA Falcon coils - Programming by 'Allan Engineering'. The intercooler core is 520mm wide, 350mm high and 50mm thick. The tanks add about 50mm to each end. Make sure you use the services of an experienced dyno tuner to program the ECU. The spark plugs that were in the RB25 engine when I bought it were NGK PFR5K. I used a plug one range colder - NGK PRF6A You will probably have dissected a couple of engines to achieve this build so have a look at the harmonic balancers and check which one matches up with the belt requirements of your accessories as the A/C pulleys can either use a 'V' belt or a flat grooved belt. The size of the heater hose fittings on the block vary too. The Skyline block has 5/8 fittings while the Commodore block is 3/4 - just to give ya the absolute shits.

Here is the circuit that I used to combine the three ignition signals to drive the tacho.

My R31 Skyline info page

R31 Skyline Club.com

A few people have asked about the costs associated with this work so here is a guide.........prices as of about 1999 / 2000

RB25 engine $1200 (Normally aspirated) - Pick one that has a removable rubber grommet in the centre of the crank angle sensor. This denotes a crank angle sensor that can be disassembled to allow replacement of the trigger disk. This may be required to keep the programmable ECU happy - depends on what ECU you use.

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