GT-R Unleashed

The first instalment of my journey with the R32 GTR (see GT-R Revisited) looked at bolt-on modifications, which yielded 280 kilowatts at all four wheels. The result was a highly driveable street car, with as good as - or better - than factory fuel consumption, and vastly improved top end power.

However, it was ultimately time to go beyond the bolt-on power-ups, and look at the engine itself.

There are a lot of options in terms of building a tough RB-series bottom end, and I considered all of them carefully before making my choice. Taking apart the bottom end also represents and opportunity to address what I consider to be some of the shortcomings of the factory RB26DETT.

One of these shortcomings is the engine’s relatively small displacement – with 2.6 litres, it doesn’t take much in the way of turbo or cam upgrades before you find yourself rowing through the gears to keep the engine on the boil. The good news is that there are options to increase the swept volume. The hard part is choosing the best option for your driving style, budget and target power output.

RB26s often have issues with oil surge, and oil pump failures. I also took the chance to improve on some of the factory oil control equipment in my build.

No replacement for displacement

Many people have achieved big numbers from 2.6 litre bottom end, and given the quality and price of off-the-shelf internal components, building a tough, fully-forged RB26 bottom can be achieved quite cost-effectively. It also allows the retention of the short connecting rods, factory rod angles, and above all, the quintessential high-revving nature of the engine.

However, using revs to achieve a given power target can be a double-edged sword. For example, running very large turbos and/or camshafts on a 2.6 litre bottom end can harm off-boost driveability. This is fine for the track but I was concerned it may be hard to live with on a day-to-day basis. While the ‘32 was perfectly driveable with its bolt-on modifications, I was not convinced that it would stay this way once I made other changes.

The next option I explored was the stroker kit. These kits are available in a range of brands, with displacement of around 2.7 - 2.8 litres, depending on the bore size used. These kits consist of a custom (sometimes billet) crank with a longer throw, as well as rods and pistons to suit. Some aftermarket stroker cranks also include additional counterweights to allow more reliable, higher-RPM operation. Prices start from around AUD$7000, which may seem expensive at first glance, but these kits usually include forged or billet rods and forged pistons, and so represent a significant upgrade over the factory gear and reasonable value.

There is a lot to recommend these kits. Retaining the standard RB26 block has many advantages over the 3.0 litre conversion (far more than I realised, it turns out – more on this later) and removes the need for a lot of custom machining and adaptors. Stroker kits have the added advantage that once they are in and running, the engine is visually indistinguishable from the OEM item.

The stroker kit was one option I gave serious consideration to before deciding on the three-litre hybrid.

A hybrid (and custom) RB26/30 uses the twin-cam RB26DETT cylinder head mated to the RB30E bottom end. The RB30E was sold locally in single-overhead-cam form in the R31 Skyline sedan and VL Commodore, and was also available in turbocharged form in the VL series.

The RB30 has the same bore as its 2.6 brother, however the longer stroke provides a ‘square’ bore/stroke relationship.

Compared to the 2.6, the 3.0 is not as rev-happy, however I was more comfortable achieving my power target through displacement rather than through RPM (either option was going to require fairly serious boost…).

Unlike in Japan, good condition 3.0 engine blocks are readily available in Australia. Since I was going to be running forged internals anyway, it made sense for me to have a complete short-motor assembled in a workshop while the car was still on the road. This would, I reasoned, keep the ‘down-time’ for the GTR to an absolute minimum.

(Note that stroker kits for the RB30 were not widely available for the RB30 when I commenced my build – it is now possible to stroke an RB30 out to 3.2 or even 3.4 litres).

Having decided on what bottom end I wanted to run, my next decision was whether to build the motor myself, or have a workshop assemble a short block built. Retaining the 2.6 bottom end, or even installing a stroker kit, would be within the reach of many competent DIYers, but the RB26/30 conversion represents an additional layer of complexity which I was not prepared to tackle on my own.

Many DIYers have completed the RB30 conversion themselves, and this task has no doubt been made easier with the increased availability of specialised conversion parts, especially complete adapter kits (including oil pickup) to mate the alloy 4WD sump to the RB30 bottom-end. I am running the ProEngines sump adapter kit, which included the oil pickup, sump adapter plate and all required bolts. The kit has had many positive reviews and recommendations on Skyline forums, and it lived up to its reputation as being a well-made and well-fitting item (note that the sump adapter moves the GTR’s alloy sump 10mm lower relative to the gearbox, and that the lower bellhousing bolts will no longer line up. The alloy sump holes need to be welded up and redrilled to suit – obviously this is easiest with the engine on a stand).

In addition to getting the components to physically bolt up, there is a lot of custom machining required for the RB30 bottom end, and making the necessary modifications to the RB30E block myself would have been time-consuming at best, and frustrating at worst. In light of this, I decided to talk to a few workshops to find out the cost of having a complete short-block built.

Endless list of options

There are a lot of variables in building an RB26/30 combo. For example, the RB30 block runs a 10mm head bolt, whereas the RB26 runs 12mm bolts. Some workshops recommend using 10mm bolts with washers in the head; others recommend redrilling the block for 12mm studs.

Some workshops are adamant that the OEM head gasket (with an o-ringed block) is optimal; others insist on running a multi-layer metal head gasket. I spoke to a lot of workshops to seek their views on my build. Some workshops gave detailed reasons for their recommendations; others were less forthcoming. Still others baulked at the prospect of the bottom end being (ultimately) subjected to up to 30 pounds of boost.

In the end I opted to have the bottom end assembled at ESP Racing. The staff at ESP were happy to speak to me at some length regarding the engine build, as well as my power target and boost level, and in the end I was confident that the bottom end was going to be able to cope with the amount of boost I intended to throw at it.

The specification of the build will ultimately depend on your power target and the boost that will be run. The entry-level price for a forged 3.0 bottom end is around $5000 (not including ancillaries or the required adapters to run in 4WD configuration) – the upper limit is as much as you want to spend!

Once you include gasket kits, a high-flow oil pump, a harmonic balancer and timing belt, sump adaptor and all the other required parts, you are looking at a minimum of $10,000.

If you are running the standard clutch, you will most likely need an upgrade, which can cost between $2000-$3000 (if buying new); or from around $1000 for a good-condition used clutch and flywheel.

Cylinder head

The other major expenditure item is the cylinder head.

In terms of the head itself, one of the most hotly contested issues in modifying GTR heads is whether or not there are benefits to be had with porting. It is clear that the factory RB26DETT cylinder head is very well designed, and has flow capabilities sufficient to support some phenomenal horsepower.

In the end I opted for a cylinder head with the ports ‘cleaned up’, but did not opt to increase the size of either the ports or the valves. I also match-ported the throttle plate to the head to minimise any flow restrictions.

There is some level of debate as to the point at which a given camshaft profile will render a GTR ‘undriveable’ on the street. However, there is some consensus that up to around 280 degrees duration will still have some level of road manners. I chose to play it safe and run JUN cams, with 272 degrees duration and 10.5 mm lift (both inlet and exhaust). By comparison, the advertised duration/lift of the RB26 factory cams is 240 degrees/8.58mm (inlet) and 236 degrees, 8.28 mm (exhaust).

A visual comparison between the factory-spec RB26 cams and the aftermarket JUN cams shows a significant difference in the ramp profile and the lift.

Note that these cams required modifications to the cam tunnels – in particular, a small section of the ‘lip’ on the cam tunnel needs to be ground down (with an air grinder or similar) to allow sufficient clearance for the cam lobes.

I am also running JUN heavy-duty valve springs which are rated as suitable for the cams.

Oil filter relocation and oil cooler

Any GTR owner who has their oil filter in the factory location will tell you that changing the oil filter is the bane of their existence. The RB26’s side-mounted inlet plenum almost eliminates access to the side of the motor. There is little joy to be had attempting to access the oil filter from below, due to the location of the engine mount, drive shafts and cross-member.

For this reason, having the engine out of the car represents a great opportunity to fit an oil relocation kit. Mounted high up in the engine bay, it makes changing the oil filter a pleasant five-minute job, rather than an exercise in contortion.

Many oil filter relocation kits can also be integrated with an optional oil cooler. I reckon an oil cooler represents worthwhile insurance, especially if you’ve just splashed out major dollars on building a tough bottom end. My ’32 runs a Trust item, which sits the oil filter just to the rear of the battery. It includes braided lines that go all the way across to the passenger side guard, where the ‘cooler sits behind a vent in the front bar.

Bear in mind the volume of oil held in the lines will increase the volume of oil required at service intervals.

Oil pump

Numerous reports of N1 oil pump failures led me to the German-made Nitto oil pump. At the time of purchase, it was more than three times the cost of the N1 item, however I didn’t want to take any chances when it came to the oiling system and most workshops agreed it was a sound investment.

The earlier R32 GTR crankshafts a relatively narrow oil pump drive, which do not contact the full face of the oil pump gear. This has, over time, lead to premature oil pump failure in R32 GTRs. The cost-effective method of addressing this issue is to install a friction-fit “collar” over the crankshaft snout, which increases the width of the contact surface for the oil pump.

Sump baffles

One of my favourite attributes of the GTR is the ability of the 4WD system to facilitate some serious high-rpm launches. That same 4WD traction also enables some frankly ridiculous cornering speeds in long, sweepings turns. However, it also exposes a weakness of the factory sump design. On big-horsepower GTRs, hard launches or fast cornering can force all the oil to one side of the sump and cause oil starvation.

This gated sump replaces the complex GTR windage tray, and surrounds the oil pickup with one-way ‘trap doors’. These ‘gates’ slow the movement of oil to one side of the sump under big cornering loads or hard launching and therefore help ensure the pickup remains immersed in oil.

Between the high-flow oil pump, the oil cooler, the wider oil pump drive collar for the crank and the gated sump baffle, I am confident that I’ve done everything possible to maintain good oil pressure and preserve the life of the bottom end.

Rotating assembly

ESP recommended running H-beam connecting rods - also Nitto items – which have an oil squirter integrated into the side of the rod. These small channels spray oil onto the thrust face of the bore, and help compensate for the absence of oil squirters in the RB30 block.

The pistons are forged CP items, and are designed specifically for use in an RB30 using a twin-cam head. The valve reliefs are sufficiently deep to allow high-lift cams, and they maintain the same 8.5:1 static compression ratio used in the RB26.

I opted to retain the factory RB30 crank. The standard forged crankshaft from the RB30 has a reputation for being not only strong, but able to handle reasonably high RPM (allowing for the comparatively long stroke). My crank was balanced, and the bearings resized and micropolished, before being returned to the short motor assembly.

Clutch

I opted for a good-condition, second-hand triple plate clutch. Used multi-plate clutches start from around $1000, compared to a new item which would be around $3000. Be careful not to bend any of the plates when inserting the gearbox spline into the motor.

Achieving bonnet clearance

One of the more time-consuming aspects of fitting an RB30 block into an R32 GTR is finding sufficient space to accommodate the extra 38mm of block height. When installed in its factory position, the RB26/30 fouls on the bonnet, and it is also difficult to reconnect intercooler and radiator plumbing.

The R32 GTR bonnet is made out of alloy, and is susceptible to warping under high heat. It is therefore not a straightforward matter to simply modify the bonnet (e.g. by welding in a ‘bonnet bulge’) to accommodate the additional deck height.

One simple option would be to replace the entire bonnet with an aftermarket fibreglass item, with the required bonnet bulge added in. However, this would markedly change the external appearance of the car and not what I was after.

I fabricated a set of 10mm steel spacers to sit between the k-frame and the chassis rails. This allowed the engine to sit slight lower in the engine bay. Once the ribs on the bonnet were relieved, there was just enough clearance to shut the bonnet.

Unfortunately, I had to remove the strut brace to accommodate the twin-turbo setup. I also needed to relieve the “twin turbo” boss cast into inlet plumbing. Since I will ultimately be running a single turbine, this was an acceptable (temporary) trade-off which can be addressed later.

Devil is in the detail

So far, we’ve covered the big-picture modifications that are involved in running an RB30 in an R32 GTR. But there is a long list of small, but time-consuming, modifications that are required before you hit the road.

Even if running the RB30 lower timing belt cover, it needs an extension plate welded in to cover the timing belt. There is no provision on the RB30 block for the turbo support brackets, so the existing ones need to be modified to suit. There is only one oil drain on the RB30 block, and so a twin-turbo configuration requires the use of a T-piece.

There are also a number of changes required to accommodate the additional 38mm clearance between the block and the head.

Due to the additional block height, new oil and water feeds and drains are needed for the turbos – the existing hard lines will not flex enough. Be sure to use high-temp oil hose for the drains, wrapped in heat wrap. Some of the under-plenum water lines also need to be extended to accommodate the extra height. And of course the intercooler plumbing will need to be modified or replaced. If you were running a top-mounted “Autech”-style catch can on your 26, you will need to find some other way of trapping those blow-by vapours – and an appropriate spot to mount it in the engine bay – as there is not enough bonnet clearance to mount it above the cams.

The RB26 power steering pump bracket needs to be modified to fit the RB30 block – an RB30 bracket will not work. The exhaust manifold flanges need to be modified to clear the block. The RB30 crank uses a different crank bolt than the RB26, so be sure to get one of those. And the knock sensor mounting bosses on the RB30 block are different diameter and thread to the RB26, so an adapter is required. And the existing ‘Y-pipe’ – connecting the turbo dump pipes to the main section of the exhaust – will not fit without modification (the extra deck height moves the turbos up, and the Y-pipe fouls on the firewall).

While these may seem like minor hiccups, each problem is time-consuming and frustrating to address, and above all requires a fairly well-equipped shed and some ingenuity. At many points during the process, I looked back and thought “if only I had opted for the 2.8 stroker kit…”

Fuel

The Tomei fuel pump now serves as a lifter pump to feel two DeatchWerks 300lph fuel pumps, fitted inside a Sard surge tank. ESP supplied and fitted both pumps, a used Sard surge tank, and installed the system in the boot of the R32.

Tuning

With the engine installed and filled with run-in oil, it was back to ESP Racing for Glen to do the run-in tune (Glen did not recommend driving the car to the workshop as the more aggressive cams would require tuning to run safely). Once the run in tune was done, the seemingly interminable task of running-in the motor began…

Results

There were many stages throughout the RB30 conversion where I seriously questioned whether I had made the right decision. Although the RB30 is the same family as the RB26, making the RB30 fit into the R32 GTR is fiddly and time consuming, and a lot more difficult than many internet build-threads might have you believe. I have tried not to gloss over the difficulties of this conversion.

Although I am very happy with the results I have achieved with my 3.0 conversion, I would advise anyone considering their options to think carefully before discarding the 2.6 block.

There are also other tradeoffs in terms of driveability (these issues would occur regardless of how the power level was achieved – 2.6 or not). Compared to the OEM clutch, the HKS item has a quite abrupt engagement, and is heavy to operate, particularly in traffic. It is definitely no longer possible to crawl along in peak hour traffic for any sustained period.

After around 4000 rpm in either first or second gear, the nose of the GTR starts lifting noticeably, and the steering becomes very light (almost ineffective). More careful use of the throttle is now required around corners – the rear end is now very willing to step out if the steering angle is too acute. I will definitely be focussing my attentions on the suspension and tyres before adding any more horsepower.

The newfound power and torque also comes with a significant increase in fuel consumption – from around 10 litres per hundred kilometres to perhaps 14 or 15. While the fuel consumption is probably acceptable in absolute terms, this represents a surprising large percentage increase. It’s also worth noting that with an oil cooler and the sump adapter in place, the required volume of oil at each oil change is up to 7 litres – which is a substantial cost per oil change when running Motul oil.

Now for the good news…

The Vi-PEC engine management system (together with Glenn’s tuning prowess) does an impressive job of handling the lumpier cams and 1000cc injectors, with a low and stable idle. The idle is notably lumpier, but not unpleasantly so.

In terms of on-road performance, the RB30 is a different animal altogether.

Even with the larger cams, it no longer has the low-rpm doughiness of its 2.6 litre brother, and boost comes on faster and stronger. Although the longer stroke of the RB30 requires a somewhat conservative rev limit, there is a much wider power band available for use. Even in day-to-day driving, far less thought is required from the driver’s perspective in terms of selecting appropriate gears. It is now possible to cruise along comfortably in fifth gear at 60 km/h, with the engine just barely ticking over above idle. And it is now all too easy to flick the back end out to get around corners and roundabouts with a quick dab of the throttle. In these respects, the road manners are superior in terms of day-to-day driving.

A quick inspection of the dyno chart speaks for itself. The power curve is now much flatter with stronger mid-range, and the torque curve is higher and flatter. Boost comes on much sooner, giving a much broader power band.

Peak boost is raised to 22 psi, producing a tyre-shredding 383 kW.

Undertaking an engine conversion of this type clearly represents moving beyond the basic bolt-on mods - and with that comes significant cost and effort.

Even assuming you already have upgraded all the necessary ancillaries referred to in the first story (ECU, injectors, intercoolers, etc) and are doing the installation work yourself, an engine conversion of this type probably demands a budget of around $15-$20k, depending on the types of components chosen (note though that a substantial part of this cost could be recovered by selling off the 2.6 litre motor). And then there are engineering costs if you want to have your modifications certified for street use.

But, given the results that can be achieved, this can be a very worthwhile and satisfying investment.

Thanks to: ESP Racing http://www.espracing.com.au

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