Nissan RB30 
 Twin Cam Head

This conversion was achieved using a naturally aspirated RB25 twin cam head without variable valve timing. This allowed the use of a standard 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 valve springs were quite soft at 39 Lb. which limited performance. A set of GTR springs were fitted.


Before you dismantle anything !

**Note carefully the position of the eccentric in the tensioner in its tensioned position so that
this can be replicated when the tensioner is in its new location above the water pump.**

If you need to remove the RB25 inlet manifold, do it carefully so as not to damage the gasket as they are difficult to get hold of and insanely expensive. Alternatively you can just use a thin bead of sealer instead of the gasket as the machined surfaces are very good.

Be careful when removing the RB25 head bolts. The head bolt washers are not captive on the head bolts and are difficult to remove because they are recessed deep in the head. Be sure to pick up the washers after removing the head bolts. Don't leave them in the head and then try to tip them out later as they will disappear inside the head and can be just a little difficult to find and remove. A magnetic pick up tool or clasp might be useful here.
The RB25 head bolts need to be used as they are much shorter than the RB30 items and sit much lower in the RB25 head.

While the lid was off I threw in a set of 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 !

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 the tensioner and the idler are too close together. The tensioner is moved to a new position above the water pump to waste a small amount of belt length because I could not find a belt a couple of teeth shorter. A hole has to be drilled and tapped for the tensioner. Its position can be determined once the appropriate cam belt is obtained. The block is thick enough here to drill and tap a hole for the original tensioner mounting stud. I've included dimensions here that were used on my engine, however they should only be used as a guide !

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 its tensioned position ) 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.



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 !

An RB20 turbo exhaust manifold can be used as this just bolts straight on. If you're keen, then you can make an extractor style manifold from steam pipe. A Turbonetics wastegate has since been fitted to the exhaust manifold to control boost.

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


The RB30 lower timing belt cover can be used. The RB25 upper belt cover can 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.


The RB25 fuel rail accepts o-ringed injectors. There are some large Mazda RX7 injectors available that will fit (12a turbo I think).

Here the new engine is lowered into place before going off to the engine dyno to check clearance around the turbo and inlet manifold.


Dyno Chart

Dyno Chart

Premium unleaded - 17 Psi boost
467 Hp @ 6000 rpm
456 ft/lb @ 4500 rpm
Purrs like a kitten
& pulls like a cut bastard !


Please note this is a copy of a page from another site " " I meggala did not write this information I copied it as a reference as people have shown interest in this conversion and links and info sometimes get lost . The link to the original site is at the bottom of the page. If any one has a problem with me hosting this page mail me and I'll remove it meggala

If any one has any other info re this engine please let me know and I'll link to your site or host the info. There is some one in qld who hads done this conversion using the later model head with the
variable timing it is a non turbo. the comment was made he used a oil line to activate the
variable cam timing .( I no expert jsut passing the info on) and it goes very well but no power
figure yet. I would love to see I feel this would be a great n/a engine.
anotehr note for N/A people he used the stock rb25 N/A pistons in the rb30 block (same bore) the compresssion was 10.5 to 1.
also this engien currently holds the 2wd skyline record in Australia 10.51 seconds (using and auto box and slicks

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This page was last updated 07/11/2000