06/04/2013
The OEM Subaru block uses a cast in iron liner, which is similar to a Honda, as an example. Unfortunately the Subaru liner is cast in below the deck surface by .090". This exposes the Aluminum at the top of the cylinder to the combustion chamber area making it weak and prone to cracking when any sort of high cylinder pressure is applied to it. There are exceptions to this with certain, nearly un-obtainable, subaru castings.
For most applications the stock liner is a good combination but far from being the best. Installation of the sleeve is key and so is proper "abuse". Any casting has flaws, so there are failures just as there is with any OEM aluminum cast block with sleeves. That's why virgin cast or billet aluminum is used for super high end race stuff.
It is imperative that everything is 100% correct to "reduce" the risk of an improper sleeve installation but there are many other factors just with the casting that are just inherent in using a recycled, low quality material to cast the block in-the-millions and drill a bunch of holes in it.
With that said sleeves are the only way you will have cylinder integrity and make serious power in an OEM casting. Sometimes, you may need more than one to get to your goal and that's nobody's fault but the OEM manufacturer for making a mediocre product to start for under a 1000$ the rest of the time somebody was being human.
Experience sleeving 100's of them since 05' , I have been able to watch the evolution between casting years and noticed a trend that Subaru was determining flaws in their products and made changes to reflect a higher quality part but it still isn't perfect. I have also learned from our mistakes several times. One that sticks out is to not sleeve castings earlier than 702' without warning the customer first at what may happen and why it does it.
Howard
