Finding the Balance Between Performance and Reliability: The IAG 550 Short Block versus the STI Type RA Short Block
If you’re like a lot of Subaru enthusiasts, you’ve likely spent a fair amount of time (and money) trying to eke out every last bit of horsepower by modifying your OEM Subaru engine. Finding that balance between power and reliability can be an artform, and there is always that possibility that you’ll end up pushing your engine past its breaking point. These things happen, and when they do, it’s definitely time to reconsider what your new set up should look like.
THE IAG 550 VS. THE STI TYPE RA
We’re often asked if the STI Type RA Blocks can hold as much power as an IAG 550 Short Block, and while there are reports that the RA blocks can handle up to 450whp, the real question is whether it can reliably handle the additional power. In this article, we’ll take a comparative look at the IAG 550 Short Block versus the STI Type RA block to help you find the optimal balance between performance and reliability in your Subaru build.
Shop Now
STI TYPE RA BLOCK
The STI Type RA block made its debut in 2018 in what was supposed to be a limited edition run, but became a regular offering in all the STIs from 2019 on. While the stock RA only made 5 more hp than its STI predecessor, it was hopeful that the 2.5 liter turbo boxer engine with 310whp would be capable of accommodating additional power without the risk of a catastrophic engine failure.
Shop Now
THE WEAK SPOTS
As the piston ringlands have long been a common point of failure for many a Subaru engine, Subaru attempted to address this issue by equipping the RA with a fortified piston that could stand up to extra load on the motor. Unfortunately, the pistons in the OEM Subaru STI EJ257 and the RA blocks continued to be produced using a hypereutectic cast design. This casting method is susceptible to irregularities in both the casting process and the materials used, leading to potential weaknesses in the pistons. While an additional 10 grams of aluminum was added to strengthen the wrist pin area of the RA pistons, the new design still didn’t address the failure-prone ringlands or the casting imperfections.
We've got you covered for all your maintenance needs-
Shop Now
A GOOD DEAL?
From an economic standpoint, the RA may initially seem like a pretty good deal. Not only do they cost less than the IAG 550, but there are plenty of power-boosting options available. The thing to keep in mind, however, is that the RA blocks only come equipped with the basic OEM components- from bearings, to the crankshaft, to rods, the only upgraded internal components are the structurally modified pistons. This means you’d be getting an engine that is still susceptible to failure due to cracked or broken ringlands or a spun factory rod bearing. This brings us to another crucial point to consider, which is the fact that Subaru does not warranty their engine blocks, even if they’re brand new and direct from the factory. (Unless the block is installed in the model of car originally equipped with the same short block.) This doesn’t mean that the Type RA doesn’t have its place, but without spending to upgrade the internal components, there’s sure to be costly issues if you’re using it aggressively (which you most likely are).
From air oil separators to oil pans, IAG has you covered for all your Subaru oiling needs-
