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Street Spec Value Shortblock

Our Street Spec Value series short blocks are designed as an ideal compromise between cost and performance for less demanding applications. This revised version now features a lighter yet more detonation-resistant Cosworth "boxed strut" piston. Piston skirts are Xylan coated for reduced friction and tighter clearances. Connecting rods are a low cost Manly H-beam 4340 rod with increased strength and rigidity over the stock rods. The OEM forged and surface hardened crankshaft runs in King XPG tri-metal race series bearings.

Every short block is professionally assembled from all new components in our dedicted engine building room by our in-house builder who has 18 years of motorsport level Subaru engine experience and has built over 500 Subaru high performance engines. Every short block is blueprinted to carefully designed specifications that balance extended service life with extreme power capabilities. Every dimension is logged and a build spec sheet is provided for reference. The block is assembled with all necessary block hardware and oil separator plate.

Click here for shortblock comparison chart.

Usually ships in 4 to 5 days.

Manufacturer: RalliSpec

  • Subaru WRX STI MY15-17
  • Subaru Impreza STI MY01-14
  • Subaru Impreza WRX MY06-14
  • Subaru Legacy GT MY05-12
  • Subaru Outback XT MY05-09
  • Subaru Forester XT MY04-13

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). We fully stand behind the quality of our short blocks but there are many factors outside of our control that will contribute to or detract from the reliability and life expectancy of the engine. Poor tuning, improper or lack of maintenance, failure to select the proper supporting components for the power output, or engine cooling issues are often the culprits behind many engine failures. However, we understand the frustration a customer might experience after investing a significant amount into a built engine only to have it fail. Therefore, we will provide a one-time reduced cost rebuild service if a customer has suffered a failure outside the warranty period and unrelated to any assembly or parts quality issue. With this service we will cover all labor costs and charge only any parts or outside machining costs required and those charges will be at our cost. To receive this service the short block must be shipped back to us in the same state of assembly as it was originally sold. All external parts should be removed unless otherwise agreed upon in advance. Short blocks that have been disassembled or otherwise tampered with will not be eligable for this service.

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.

Do you use the nitrided factory crankshaft? Subaru has switched between nitriding and induction hardening processes for their crankshafts. Both processes increase the surface hardness of the crankshaft for strength and wear resistance. The depth of the surface hardness may vary depending on the process but is generally not very deep. We use whichever hardened crankshaft happens to be available and currently that seems to be the nitrided variation. We have found no significant advantage of one over the other.

What is the balance process used when building this short block? Street Spec Value short blocks have the piston weights matched to 1/2gram and connecting rod weights matched to 1 gram end to end. Additionally, the engine is assembled so that reciprocating components are installed to achieve the best possible overall balance (when dimensional considerations do not conflict). For example, the lightest piston pin is installed in the heaviest piston and the lightest piston and pin assembly installed with the rod that has the heaviest reciprocating weight. Rotating weights of the 2 rods on one side of the crank are selected to best match the 2 rods on the other side. Dynamic balancing of the crankshaft is left at factory tolerance.

Is the block honed? The block is not honed unless we find excessive distortion or an inability to achieve our desired piston-to-wall clearance within a tolerance of +/- 0.0002in. The price of this block does not allow for this machine work unless absolutely necessary. However, be assured this short block is far beyond the "drop in piston" short blocks competitors are selling for the same price.

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. Target piston clearance on the Street Spec Value 2.5L short block is 0.0027" with Cosworth pistons.

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 with more limited after-sale support. We feel that our off-the-shelf engines represent the best possible combination of components and processes.