ABOVE: The induction flow path has been 'reversed' compared to the more traditional aftermarket front mount intercooler setups of this kind - In my own arrangement, I have left the intercooler as the last component before the flow entering the throttlebody to avoid heat soak suffered by the intercooler piping travelling over the top of the radiator. I have also wrapped that section of piping with fibreglass exhaust wrap to reduce the effects of heat soak even further, what you can not see is the additional ceramic coating performed to the piping under the fibreglass wrap !
ABOVE: I fabricated a custom aluminium oil catch and mounted it to the top of the radiator via a common bracket, this currently has a breather / filter in the photo, but has already been replaced with a barb fitting and plumbed back into the inlet pipe behind the main air filter / air flow meter. An engine damper was added to protect the engine & transmission mounts from the sudden rocking motion caused by the high rpm gear changes - a worthwhile investment for a small outlay.
ABOVE: Besides the stitch-welding of the sheet metal sections around the strut towers, a Nismo strut brace was added for additional stiffening of the front suspension mounting points. This strut brace also has a built-in brake booster support bracket and when properly tensioned up, this helps prevent excess flexing of the firewall area caused by the 'stomping' action of the brake pedal during 'hard driving'.
ABOVE: I fabricated a custom aluminium oil catch and mounted it to the top of the radiator via a common bracket, this currently has a breather / filter in the photo, but has already been replaced with a barb fitting and plumbed back into the inlet pipe behind the main air filter / air flow meter. An engine damper was added to protect the engine & transmission mounts from the sudden rocking motion caused by the high rpm gear changes - a worthwhile investment for a small outlay.
ABOVE: Besides the stitch-welding of the sheet metal sections around the strut towers, a Nismo strut brace was added for additional stiffening of the front suspension mounting points. This strut brace also has a built-in brake booster support bracket and when properly tensioned up, this helps prevent excess flexing of the firewall area caused by the 'stomping' action of the brake pedal during 'hard driving'.
Initially, I wanted to build a crazy all-out power monster with over 400 kw at the wheels, this was inspired by a friend's R31 which pushes out this kind of power with an old 1986 Aust-spec RB30et engine still running the single cam head.
I started doing research on the components that was required to generate this kind of power. During this time, something that kept crossing my mind was the possibility that I might need to replace the 2.5 litre bottom end with a 'stroker' crankshaft and connecting rods in order to produce more torque. To make big power, you need a big turbo and big capacity will be needed to support it all.
To understand how all these factors work together, first you have to understand the fundamentals of how turbochargers work. A turbocharged engine work very differently to one that is naturally aspriated. A traditional four stroke engine relies on the downward motion of the piston to draw fresh air supply into the combustion chamber, when this happens, the amount of oxygen that is available for the engine to process is directly proportional to the size of the combustion chamber. Because of this, the maximum power and the rate of this power being made by the engine is limited by the amount of air the engine can effectively 'swallow' at any given time.
Have you ever felt a car running much better on a really chilled cold night ? This is because air molecules contract or shrink when it's cold, so more air molecules are being sucked into the engine and effectively producing a more efficient combustion process. Now, a turbocharger is essentially an air pump driven by the exhaust heat (YES - it's the HEAT produced by the engine's exhaust that effectively spools the turbocharger and not so much the exhaust pressure what a lot of us are made to believe, but more on this later...). As the harder the engine works, the more air the turbo pumps into the inlet system for it to combine with fuel to make power.
Now, to really think about it, if a turbocharger can get more air 'pumped' into the combustion chamber compared to a non-turbocharged engine of the same capacity, more oxygen is therefore available to be processed with the fuel to make power. So by rights, less fuel is required to do the same amount of work in a turbocharged engine compared to one that is not turbocharger driven. If not driven in a spirited manner (ie thrashed), a turbocharged engine is considered to be more efficient. This is why it is a good idea to have a switchable solenoid installed so a low boost setting can be selected just for everyday driving if needed be rather than have the engine running on higher boost setting all the time.
Now, choosing the number and size of turbochargers for a given application is an art on it's own. It all comes down to deciding on what the car will be used for. The two main configurations for the six cylinder Skyline engine is a big single or a pair of smaller 'twins'. Both have it's pro's and con's.
Out of the two setups, the larger single turbo is the easier to implement in terms of hardware plumbing as it's less complicated compared to the twins. However, due to the tight layout of the engine bay, the only practical way to mount the big single is high up next to the rocker cover of the engine - this is also the quickest way to get into trouble with the law as police officers love to 'defect' cars modified in this manner (The cops aren't dumb anymore and know what they're looking at and what to look for !). Due to the larger internal components of the big single, it doesn't tend to hit full boost until higher up in the rev range - upwards of 5,000rpm is quite common, but when you get there, you'll know about it because the sudden rush is sometimes considered as 'addicitve'. This is why the big single is a configuration more suited for drag racing where cars can be set up using a stall converter with an automatic transmission. My friend's R31 drag car is in this catagory with it's strengthened and manualised automatic transmission that's also converted with a 'transbrake' - where the gearbox can be engaged in both 'Drive' and 'Reverse' at the same time, the car is then stalled to the pre-set rpm at the start line, when the start lights go green, reverse is then released via a button on the steering wheel. With this system, you would get perfect launches each and every time.
As with the lag that is associated with the big single, the only way to bring full boost in earlier in the rev range is to increase the capacity of the engine - picture this as increasing the size of the 'lungs' of the engine. With Nissan's RB engines in the Skyline, there are essentially two ways this can be done. The first is the expensive way. You start off by hunting down a (preferably new) RB26 N1 block, this is the strengthened version of the RB26dett that came out in the R34 GTR N1, then a special aftermarket kit made by OS Giken in Japan is installed. This stroker kit consists of a special deck extension which is added onto the top of the RB26 block using strengthened dowells and larger diameter head bolts along with custom cylinder sleeves / liners, this basically increases the deck height of the 2.6 litre block to the taller configuration in order to support the longer stroke configuration of the 3 litre billet crankshaft. OS Giken recently updated their catalogue with a 3.15 litre rather than the older 3.0 litre setup. There are various custom shops (RIPS in NZ is one) that have released their own versions of this setup ranging from 3 litres up to a huge 3.4 litres ! Having said all that, this kind of setup is not cheap as OS Giken has a $15,000+ price tag on their short block alone.
The second method to this madness is to go down to the local wreckers if you are lucky enough to be living in Australia and hunt down a 1987-1988 model Holden VL Commodore or Nissan R31 Skyline with a 'series II' short block. You basically need just the block and crank as aftermarket conrods and pistons (original 2-valves-per-cylinder pistons for the single-cam head can not be used with the twincam head to support 4 valves per cylinder) would be required in this application anyways. The objective here is to collect the pieces to build a RB-hybrid. This involves removing the single cam head that was originally on the RB30e / RB30et engine and grafting on a twincam head from the later model RB25 or RB26. The preferred choice is the RB30 block from the later model 1987-88 series II VL Commodore as the required oil supply and return holes for the turbocharger is already there. This is the same RB30et block that Holden used for the VL / Calais turbo.
Due to the taller deck height of the block to accomodate the longer stroke of the 3 litre engine, a longer timing belt is required. An additional belt tensioner is therefore required to be installed. To fit this, a hole is required to be drilled and tapped to the forward facing surface of the block. The exact position of this tensioner is available from various forums. The series II block has this required front face already in place, so just drill, tap and install.
When using a RB25 head, if possible, find one from a earlier non-turbo version of the R32 GTS - there was a 2.5 litre non-turbo version of the R32 that pre-dates the variable valve timing (VCT) system, this is the ideal choice as no modifications is required to the oil gallery passages that meets up with the RB30 block - a job that is necessary on the later VCT-equipped RB25 heads if one is to be used in such a hybrid build. Welding and modifying of the block and/or head will be required.
The RB26 head from the twin turbo GTR is not VCT equipped but however has head bolts with larger diameter, so larger holes are required to be drilled and tapped into the RB30 block to accomodate this difference if the RB26 head is used. Even tho the two heads are similar in design and the one obvious difference already mentioned is that the later RB25 heads are VCT equipped, there are still several major differences between the two. The first being that RB25 heads are equipped with hydraulic lifters and RB26 have the solid type. This is why the RB26 is equipped with a camshaft profile more suited for a higher rpm redline. Another difference is the mounting patterns of the inlet and exhaust manifolds. The actual positions of the ports are pretty much identical between the two, but there are minor differences between the positions of a couple of the mounting studs. From the factory, the RB25 is equipped with a single throttlebody whereas the RB26 has six individual butterflies. Adaptor plates are available from various Japanese parts suppliers to allow mixing and matching of the induction componets between the two heads. The same goes for the exhaust / turbo manifolds. The mounting stud positions are identical except for two that needs to be reversed. This is why some aftermarket manifold manufacturers release manifolds with 'universal' flanges that includes two sets of mounting holes on the one flange to suit both heads.
Now the two major components of the head and block has been chosen, the rest is just pretty much ordering and playing the waiting game for it all to arrive in the post. The rest of the components that need addressing include forged pistons, billet / forged con-rods, camshafts, inlet / exhaust valves, bearings, head / rod bolts / studs, etc etc.. These are available from a large variety of sources and are pretty much 'you get what you pay for'. So choose wisely - 'reliablility' is the key word with any performance engine build.
At this stage, I have decided to stay with the 2.5 litre block for now. After much research, I've discovered the longer conrods of the 3 litre bottom end suffer from excess loading when rev'd. For performance street tuning, the 2.5 litre setup is more than sufficient for the required drivability. I want to see what damage I can cause first with the current configuration.... I plan to transplant this engine into my other car at a later date - a 1988 VL Commodore and perhaps build a twin turbo Nissan V8 for this R33. The Nissan V8 engine I am considering using will be similar in design to the engine that Nissan is currently using in the Australian V8 Supercars series, based on the current Infiniti eight cylinder platform.