Editing Twin Cam conversion

[[Category:Engine]]
[[category:RB30E]]

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 [[RB30E]] 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.

RB30 combustion chamber = 55cc
RB25 combustion chamber = 63cc
This was determined by measuring the cubic capacity of the combustion chamber.
This is done by turning the heads, RB25 and RB30 upside down and placing a piece of perspex with a small hole in it over the combustion chamber.
A syringe is then used to inject oil through the hole in the perspex into the combustion chamber until it is full.
As the syringe has CC's marked on it, you just add up how much oil you have injected.


'''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.

*On the RB25 engine, note the position of the cam gears with the engine at No.1 TDC. The dot on each gear should line up with a mark on the timing cover back plate. Mine were close but not exactly in line, so draw yourself a diagram or take a photo if this is the case to help during assembly.


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 chopper 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.

'''Note:'''
The water outlet on the RB25 manifold sticks out a lot further than on the RB30.
You might need to work a bit of magic with the top hose fitment.
I modified this area to get the outlet closer to the manifold due to space restrictions in the vehicle.

Also, the RB25 block has a longer dipstick and tube so that it clears the inlet manifold.
Which, together with the twin cam head is wider than the RB30 manifold/head.
The longer dipstick set up should be transferred to the RB30 block - to make things easier in future.

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.

A deflector plate was inserted into a slot that had been milled into the bottom of the plenum chamber behind the throttle body. This is to disperse the boost flow inside the plenum chamber and prevent the pressurising of the two runners directly opposite the throttle body.

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.

[[Image:Tc1.jpg]]

While the lid was off, I threw in a set of  ' Custom ' Wiseco forged slugs in
anticipation of things to come.

[[Image:Tc2.jpg]]

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.
A hole has to be drilled and tapped for the tensioner.
Make sure that adequate tension can be gained when determining the location for the stud.
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.
A machine shop could drill this for you, but I just lined it up by eye with the help of a friend.
I've included dimensions here that I used on my engine, however they should only be used as a guide!
Have the eccentric in a slack position and the belt tight by hand when setting up, so that you can gain adequate tension when you swing on the eccentric in the tensioner.

[[Image:Tc3.jpg]]

[[Image:Tc4.jpg]]

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 (Suits: Audi A4 1995- Volkswagen Passat 1998-).
A VL turbo oil pump was used.

[[Image:Tc5.jpg]]

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 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.

[[Image:Tcwg.jpg]]

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

[[Image:Tc6.jpg]]

Here the old turbo was bolted on so that I could set up its plumbing &amp; check clearance in the car.

[[Image:Tc7.jpg]]

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.

[[Image:Tc8.jpg]]

The RB25 fuel rail accepts o-ringed injectors.
There are some large Mazda RX7 12a Turbo injectors available that will fit.
Make sure you obtain the connectors if you use these injectors.

[[Image:Tcinj.jpg]]

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.

[[Image:Tctrialfit.jpg]]

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'm using a plug one range colder - NGK PFR6A.

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.

[[Image:Tc-circuit.jpg]]

Dyno Chart

[[Image:Tc-dyno.jpg]]

Premium unleaded - 17 Psi boost
467 Hp (348Kw) @ 6000 rpm
456 ft/lb (618Nm) @ 4500 rpm

==Cost involved==

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 chopper disk.
This may be required to keep the programmable ECU happy - depends on what ECU you use.

*ECU                             $1800 (Autronic)
*Forged pistons             $1500
*RB30 Turbo oil pump     $550
*Bearings                         $200
*Valve springs                  $438
*TO4E Turbo                 $1200
*Waste gate                     $825
*Platinum spark plugs         $80
*RB20 Turbo exhaust manifold $100
*Exhaust manifold gasket     $32
*Head gasket                     $70
*Timing belt                     $30
*Rod Bolts and Nuts         $90
*EA Falcon coils             $250
*Coil connectors             $45
*Plug leads                     $45
*Thermostat                    $40
*Rear main seal                 $20
*Water pump                 $100
*Acid bath block             $40
*Welch plugs                 $20
*Speedi sleeves for front and rear seals     $92
*Oil, oil filter and coolant     $75
*Exhaust manifold studs     $17
*Dyno work                     $800

'''Compiled by'''

Rowan


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[[Image:Twincam.jpg|240px]] [[Image:Twincam2.jpg|240px]] [[Image:Twincam3.jpg|120px]]

''Magazine article from "ZOOM"''