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This article was first published in 1998.
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With world-class engine management, advanced turbos and a thorough engine build, we saw AVO extract 705hp from this Godzilla motor. That's 526kW, or around four times the power of your average family car! Its specific power output is even more astonishing - 235 horsepower per litre! A 200SX can muster 'only' 100 horsepower per litre... What other streetable engine could even begin to compare?
Australia's Advanced Vehicle Operations (AVO) has been involved in creating some of the most awesome hi-tech weapons in the country. A twin-turbo Honda NSX, various modified Subaru WRXs, Mazda RX-7 turbos, Skyline GT-Rs - the list goes on. Here we'll show you the ingredients AVO used to cook up a 705hp Skyline GT-R engine - an RB26DETT six cylinder twin turbo.
Intended primarily for 'road rally' events, the big-horse engine had to have very good response and a progressive torque curve.
Terry was proud to state that after all the mods, the shape of 'their' torque curve actually looks very similar to the factory's.
The first step in making a mega-hp RB26 was to fatten its swept capacity to around 3 litres - a relatively common exercise in Japan. This high torque approach was taken to reduce the revs needed to develop the power - Terry says if they were to rev the standard 2.6 engine to around 9500rpm, bearings and assorted engine internals would be liable to break. To achieve the torque figures needed, a larger capacity RB30 3 litre bottom-end was prepared. Because it uses smaller head studs than the RB26, the block had to be drilled and re-tapped to take this DOHC head. A custom timing belt also had to be fitted.
The RB30 block wasn't designed to suit the GT-R's 4WD chassis and so the original GT-R sump needed to be bolted under the engine using a 10mm girdle, which also supports the main bearings. An external oil pick-up is used as part of this custom fabrication.
For total reliability, Argo bolts and chrome-moly rods were fitted to the standard RB30 crankshaft, while ACL bearings were used throughout the bottom-end. Atop of these, APEP forged flat top pistons and gapless rings slide in the 15 thou over-bored block. The compression ratio of 7.5:1 gives a good compromise between driveability and outright power. In anticipation of over 20psi boost, a Japanese-sourced 1.2mm stainless steel head gasket was used.
The alloy twin-cam RB26DETT head received a mild port and polish job that was performed in-house. Terry says the standard head flows quite well - but that things can always be improved!
Wanting to have few limitations to using high revs if they were actually required, stronger valve springs were inserted to prevent the valves moving up and down when they weren't supposed to. Both the intake and exhaust valves are standard. Terry commented that this type of DOHC engine is sensitive to cams and timing, and he fitted AVO's own vernier cam sprockets to the custom 25/65 cams, which have mostly secret specs.
In the engine's first guise, air was forced through by a pair of AVO roller-bearing 350hp turbos. However, larger units were needed later replaced these - but we'll come to that in a moment. The original cast exhaust manifolds were retained, having their faces ground flat and offered up to the head. After passing through the turbine and wastegate, substantial amounts of exhaust gases rush through AVO-fabricated elbows, culminating in a big four inch diameter pipe. Off the dyno and on the road car, a twin three inch exhaust system will be fitted to the GT-R.
The turbochargers pump simultaneously, sucking through two large K&N filters at the end of short lengths of mandrel bent pipe. Compressed air from the turbos enters a single "as-big-as-we-can-fit" AVO air-to-air intercooler - which Terry says flows 600hp with only a 0.5psi pressure drop across it! All of the intercooler plumbing has been HPC coated to further keep temps down.
Interestingly, the mandrel bent pipes from the twin turbos lead into the intercooler core separately, but the cooled air exits through a common (larger diameter) pipe. This approach apparently prevents pulsing from the turbos. To deter the turbo units from stalling after gear changes, an AVO throttle-closed-blow-off-valve will be fitted to the intake when the engine is bolted back into the car.
Terry can vouch from experience that the standard 6-throttle intake manifold is very difficult to improve upon, and he's therefore left it in place. It must be good - how many 6 cylinder 705hp engines can get away with the standard intake manifold?!
A top-shelf Autronic SMC engine management system was programmed with the engine's fuel and ignition maps, with this process occurring on the engine dyno. The SMC also sets the rev limit to around 8000 - where the motor's torque output is beginning to drop off. AVO has fitted their own electronic boost controller to keep a tight reign on the wastegates - which might otherwise have the potential to destroy the A$25,000-odd engine. The ignition system uses the standard configuration of direct fire ignition (ie one coil per spark plug) eliminating the need for high tension leads. Colder-range NGK '9' plugs help prevent cylinder detonation.
Six Bendix 150hp injectors quench the engine's massive thirst for aviation fuel. A pair of 600hp Bosch pumps were utilised on the dyno, with the in-car pump being a single Bosch unit capable of supplying 800hp through the half-inch lines. Fuel pressure is regulated by a Malpassi regulator, which reads manifold boost pressure (clever regulator this one; I wonder if it can write as well?). At idle, fuel pressure is around 3.2 Bar (46psi), while manifold boost pressure can be added to this number throughout the load and rev range.
Once the assembled engine was ready and raring to go, Terry bolted it to the dyno and thoroughly mapped the ECU's fuel and ignition curves. Next came the power runs. At the first attempt, the engine developed (only!) 620hp at 21psi boost. Terry decided that some more fine-tuning was required and went to work on the turbo system and cam timing. Suspecting excessive exhaust back-pressure and compressor surge, he replaced the 350hp turbos with higher flowing 400hp versions and then retarded the exhaust cam timing a few degrees.
Then the dyno needle really started to swing. With around 25 psi boost the engine thumped out 705hp at 7300rpm - and could still produce 614hp at the same revs with the more conservative boost pressure of 21psi! As we mentioned, the shape of the torque curve is nearly standard, which would make this one absolutely butt-whipping road car! And the twenty-five grand expenditure? It's well spent!
CONTACT:
AVO (Advanced Vehicle Operations) - Australia
www.avoturbo.com
+61 3 9584 4499
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