In the last installment of your blog series regarding the build of our 400+ naturally aspirated 2.6L 4 Cylinder K Series engine we discussed the cylinder head for the project. Now we tackle the short block.
With the CRX chassis we have concerns over engine block deck height and fitting the package into the engine bay. We have always run K20 blocks for that reason as every bit of clearance between the engine and the hood counts for packaging. This go around we took a K20a engine block and sent it off to JBR Engines to have AEBS sleeves installed and bored out to 90mm. 90mm is about the max size that we would recommend starting with if you want the largest engine possible. It is possible to push it out to 90.25mm and even 90.5mm in the future if there is an issue and the cylinder walls need to get cleaned up for an overbore. 89mm is an even better option to give you some rebuild options going forward but will sacrifice 4-5 horsepower. An O-ring groove was cut into the block and stainless steel o-rings are being utilized as the material between cylinders with this size bore needs all the assistance it can get to keep the head gasket working properly.
The crankshaft was sourced from Brian Crower and it is their 102mm off the shelf K Series crank. We went with a 102mm crankshaft for this project based on the rule set for the class the engine is being built for. This engine is for the World Cup Finals All Motor class and calculating the weight that we believe the CRX will be raced at, the fuel allowed and horsepower potential we feel the 102mm crankshaft with a 90mm bore is the stoutest option for overall horsepower and torque while still getting a nice weight break at only 1900lbs.
With the 102mm Crank in the K20 Block with custom rods and pistons, the counterweights on the crank would have been an issue with piston contact. The crankshaft was sent to Mile High Cranks to have the counterweights cut for clearance and the entire unit rebalanced. The engine block was in the process and the crankshaft was secured so we discussed piston and rod options with Jeremy at Drag Cartel. The K20 block and the 102mm crankshaft does present some challenges and rod length is one of those. Knowing the crankshaft stroke and engine deck height Saenz was contacted for a set of custom 300m Medium Duty rods. Working with JE on the pistons Jeremy spec’ed them out for max compression and low weight.
With an engine like this you don’t just go to a catalog and pick an off the shelf option. We wanted every last horsepower so Jeremy and JE worked over all the engine numbers as far as engine block deck height, crank shaft stroke, rod length and what cylinder head is being used to build a piston that would give us maximum compression in the combustion chamber as well as designed for good piston to valve clearance for our Supertech Titanium valves to let the air in and out. What JE built is a custom 255 gram, max compression piston with DLC wrist pins as well as side skirt DFL coating. JBR Engines took all of these components and assembled the short block. Piston to Wall clearance, bearing clearances, ring gaps and all torques were carefully considered and painstakingly measured to leave no horsepower on the table. A set of Calico ACL bearings were used.
With the short block on the stand the Drag Cartel Modified S2000 Oil Pump was installed, the Drag Cartel Modified Crank Timing Gear and the Inline Pro Timing Chain Tensioner to keep the parts working reliably. After all timing guides and chains were in place the ATI Damper was installed. A Cometic head gasket was put on top of the block and the ARP Head Studs were in place ready for the cylinder head.
This wraps up what it took to build our 400+ horsepower naturally aspirated K series engine block. This engine is being built to compete in the All Motor Class at the 2018 World Cup Finals event at Maryland Intl Raceway Oct 31st – Nov 4th, 2018. Stay tuned as our next installment will discuss the external components that this engine needs to use to create the horsepower.