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Street Spec Pro Shortblock

The Street Spec Pro is the next evolution in our shortblock line. It is in response to the demand for a non-sleeved Subaru block that is fully blueprinted and balanced for more serious trackday and extreme street performance applications. The Pro version builds on the Street Spec standard unit with the addition of precision dynamic crankshaft balancing and blueprinting of the cylinder bore dimensions by going to an oversized bore. Every shortblock dimension and specification is logged and a detailed build sheet is provided with each serialized shortblock.

Click here for shortblock comparison chart.

Usually ships in 1 to 2 weeks.

Manufacturer: RalliSpec


  • Subaru

What is the recommended break-in process for the engine? This information along with warranty details can be downloaded here: Engine Warranty & Break-in Instructions (PDF).

What engine block casting is used to assemble the engine? We have no choice in the selection of the engine blocks. We purchase the current engine block part numbers available from Subaru. Currently the EJ257 blocks coming from Subaru are all "704" castings. The EJ257 block is a semi-closed deck design.

Do you use the nitrided factory crankshaft? The current crankshaft we are using is induction hardened. The nitriding process is no longer being used and those cranks are not available any more. However, the two processes are both used to increase the surface hardness of the crankshaft. We have found no significant advantage of one over the other.

What is the balance process used when building this short block? Street Spec Pro short blocks have pistons matched to within 1/4 gram and connecting rods matched to within 1/2 gram end to end. The crankshaft is dynamically balanced to 0.25 oz in.

Is the block honed with a torque plate? Yes, we always fit a torque plate during the honing process to simulate the distortion created by the cylinder head bolt torque. We suggest you indicate to us what cylinder head hardware, torque values, and head gaskets will be used so we can most accurately replicate the loads. When this information is not supplied to us our standard process is to use ARP standard head studs torqued to 90ft-lbs with an OEM head gasket.

What clearances are used for piston-to-cylinder and for crankshaft bearings? The clearances we use are based on extensive testing and experience. Oil clearances are increased over the factory settings to allow for significantly increased loads and component distortions. The engines require a 5W40 / 10W40 (road) or 10W50 / 15W50 (race) oil viscosity and a minimum of an 11mm oil pump. Piston clearances on the Street Spec Pro are set to 0.003".

What is the maximum boost pressure for this short block? We are often asked this question. Boost pressure on its own will not overstress an engine. Peak cylinder pressure after the spark plug fires will be significantly higher than any useable boost pressure. Increased boost pressures generally lead to increased cylinder pressures and heat loads which can overstress an engine. But the exact correlation depends greatly on the tuning, the type of fuel, and other factors. Its impossible to tell you what the maximum boost pressure the engine will handle will be.

What is the maximum rpm of the short block? There are many factors to consider when establishing a maximum rpm for a particular engine. Our shortblock comparison chart offers a suggested maximum rpm provided all other contributing aspects of the engine assembly have been designed to support that rpm. It is also important to understand that it makes no sense to attempt to increase revs if the engine's power is already falling off significantly or is running outside the efficiency range of the turbo. Additionally, there are often limitations in the factory oil and cooling systems that make significant increases in rpm unwise without a proper re-evaluation of those systems.

Can I substitute different pistons or rods? Our engines have been developed using what we believe are the finest components available within the target price range. In particular, when selecting pistons and rings for our Street Spec engines we took into account the desired characteristics of low noise, maximum longevity, and reduced blowby/oil consumption under typical street use drive cycles. Although we are happy to build a short block or long block to your specific requirements if you feel strongly about a certain setup, we treat any deviation from our standard engines as a custom job. We feel that our off-the-shelf engines represent the best possible combination of components and processes.