The Castrol Syntec Top Shop Challenge has become a classic game of teams and magazine staff scrambling to see who is building what type of engine and how much power they plan to make. We're not the type to beat around the bush, so we'll come out and let them, as well as our readers, know we're building our RB26DETT engine to eclipse the 1,000-plus horsepower marker without breaking a sweat. Sure, it's been done before. The RB26DETT motors have been known to hit the 600hp marker with simple bolt-on goodies but for competition purposes and looking to score big in the "Power Under The Curve" category, SP Engineering and Turbo magazine devised a plan to build a solid motor that can deliver some reputable numbers while withstanding more than a few simple passes on the engine dyno.
As we begin part one of our engine build, SP Engineering will be focusing on the RB26 cylinder head port and prepping process. The common misconception is that porting requires the ports to be as big and round as possible. Yes, producing good airflow through the cylinder head and out of the exhaust port is essential in producing big power. However, over-porting will cause an irregularity in velocity and air speed, causing the car to become sluggish at bottom to midrange power, which makes the car nearly impossible to drive on the street. Hirofumi Kondo, chief mechanic of SP Engineering takes us through the steps in building the SP Engineering/Turbo magazine RB26DETT, destined to dominate the Castrol Syntec Top Shop Challenge. In our next issue, we'll cover the bottom end buildup and what it takes to deliver 1,000-plus horsepower.
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While both RB26DETT cylinder...
While both RB26DETT cylinder heads look similar, these two sport very different port and prep characteristics when analyzed up close. For show-and-tell purposes we'll call the competitor's ported cylinder head No. 1, while the other will be known as the SP Engineering head. Never judge a book by its cover.
SP Engineering performed much...
SP Engineering performed much of the porting on the cylinder head but also commissioned Tom Fujita of Port Flow Design to touch-up any rough edges while performing a three-angle valve job and resurfacing of the head.
Notice on the factory head,...
Notice on the factory head, looking through the valve seats into the exhaust ports, the material around the valve seat juncture, otherwise known as "humps," can cause unwanted turbulence when looking to extract maximum horsepower.
Although there are many pros...
Although there are many pros and cons with removing the junctures, such as weakening of the seats and valves, this modification has been tried-and-true on many RB26 engines without any issues.
During the porting process,...
During the porting process, Port Flow tapered and cut back the valve guide sections by shaving it down to match the ceiling in order to offer a smoother transition of air entering and exiting the ports. A new set of HKS valve stem seals were installed prior to reinserting the factory valves.
Notice on the factory head,...
Notice on the factory head, looking through the valve seats into the exhaust ports, the material around the valve seat juncture, otherwise known as "humps," can cause unwanted turbulence when looking to extract maximum horsepower.
A good cylinder head porter...
A good cylinder head porter will shape the port to get the maximum flow with a minimal amount of enlargement while increasing flow velocity. Becoming overzealous in the ports and grinding away at the bowls will affect the vehicle's performance. Notice the difference in ports with the SP Engineering head compared to the previous image. Now which do you think flows more efficiently?
Hiro points toward the factory...
Hiro points toward the factory quench pad on the SP Engineering cylinder head. For this build, we plan to keep the quench area in factory specs. The reason behind the SP Engineering theory is plain and simple. The unmodified combustion chamber promotes a smaller area quench pad that keeps energy tight, compact, and ready to explode. The burn efficiency maintains optimal use of the flame and spark energy creating a full burn.
Notice on cylinder head No....
Notice on cylinder head No. 1, the combustion chamber has been modified and enlarged. We can only guess that this was performed because the previous owner was looking to produce some monster horsepower from their RB26 engine. Hiro says this type of modification is only necessary if you plan to drag race or run high boost. Modifying the combustion chambers to increase the quench zones can increase the chances of knock due to the inability to burn completely and efficiently. This modification also lowers the compression ratio, especially if both intake and exhaust sections of the chamber are cut.
Depending on the base circle...
Depending on the base circle of the cam lobes, the factory cylinder heads require machining relief pockets on each bucket for clearance of aftermarket camshafts. Here's cylinder head No. 1 with what looks like a belt grinder that was used to grind for clearance.
The stock RB26 camshaft has...
The stock RB26 camshaft has a 240/236mm duration with 8.58mm lift (intake) and 8.28mm exhaust. Hiro says if a cam has a lift of 9.5mm or larger or the cam has a base circle larger than the factory 32mm, modifications to the head are mandatory. There's also a catch when determining mods. An aftermarket camshaft that has a smaller base circle usually means it also has a higher lift such as the HKS Step Pro L 280/280mm camshaft we plan to use. The Pro L set has a 10.7mm lift (intake) and 10.3mm lift exhaust cam profile with only a 29mm base circle. This camshaft has a smaller base circler but because of the lift, it will come in contact with the head if not modified.
Hiro machined the SP Engineering...
Hiro machined the SP Engineering head using a fly cutter in preparation for the HKS Step Pro L 280/280 camshafts.
For demonstration purposes,...
For demonstration purposes, we took a HKS 272-degree camshaft and removed the bucket/shims to showcase the clearance issue if a camshaft with larger duration or base circle is used.
Hiro uses an old trick he...
Hiro uses an old trick he learned on the RB26 by taking a punch to gently secure the coolant plug on the cylinder head.
This pressed-in plug by the...
This pressed-in plug by the factory has been known to pop off at high boost pressures, causing the coolant to spill out of the engine and cause some serious damage.
Hiro prepares the cylinder...
Hiro prepares the cylinder head with a full HKS Step Pro L kit, which includes valvesprings, retainers, lifters, and valve stem seals.
The engine we plan to build...
The engine we plan to build will develop plenty of horsepower but our emphasis is making power under the curve with a high-responding motor, which will play an important part in helping us to do well in the Castrol Syntec Top Shop Challenge.
Hiro says the factory RB26...
Hiro says the factory RB26 intake valve guides are notorious for failures in high-horsepower engines. When the guide fails, the valve drops and causes catastrophic engine failure. Hiro says if the car is stock or only running an increase in boost, the factory guides will work fine.
The valves are shimmed per...
The valves are shimmed per factory specs with intake gauged at 0.45mm and exhaust clearance at 0.38mm. As a minor hydraulic shim adjustment, some shops clearance the lash closer to create an increase in lift to save in cost.
SP Engineering recommends...
SP Engineering recommends using NGK spark plugs for any RB26 engine build. NGK plugs with a heat range of seven or eight are a good choice for those who have an engine with minor engine work or turbo upgrades. For drag racing applications SP Engineering recommends going with a nine- or 10-range plug and everyone should stay away from iridium and stick with platinum plugs. The more serious plug used in F1 Racing, World Rally Championship, and MotoGP is the NGK race plug, which lacks an electrode tip that would otherwise break off or melt from the severity of the engine. These are the highest-level spark plugs that NGK has to offer.