Nissan RB26DETT - Castrol Syntec Top Shop Challenge

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 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 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 head using a fly cutter in preparation for the HKS Step Pro L 280/280 camshafts.

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 learned on the RB26 by taking a punch to gently secure the coolant plug on the cylinder head.