What HP Can Stock Pistons Handle???
 

Hey guys, I tried doing a search on the site, but I couldn't find what I was looking for. In short, I was wondering up to what HP stock pistons can handle on our FR-S, BRZ and 86's? I spun a bearing on my rods and will be getting a rebuild in a month or 2. I have a Sprintex SC with a 75mm pulley and I run E85 almost all the time. Anyway, I want to get new rods and bearings. A crank shaft may be necessary, but unknown at this time. So the question remains what HP can the stock pistons handle? I suppose I could go for forged pistons, but I want to have all the facts before I make a decision on my purchases.

Does anyone have any information regarding the stock pistons? Thanks.....

The limit on most builds is the rods, followed by fueling. I'd say you're going to want some 10:1 or 9:1 forged pistons since you're building it anyways. No point building with rods and bearings that can handle 500+ HP when the compression ratio is going to severely limit your ability to reach 500HP safely.

Well, I'm not looking to go that high at all. I'm fine with 300WHP that the 70mm pulley would give me, though I probably wouldn't use it. 72mm is what I will probably end up using and I'm already using a 75mm pulley. I always knew what I wanted for this car when I got it. A Sprintex SC and for 3-1/2 wonderful years I had the power that I was comfortable with in such a small package of a car. I estimate based on all that I have read as well as all of my bolt ons (particularly the exhaust system) that I probably was putting down 270 WHP with E85. I really wouldn't want to go much beyond 300WHP if at all. This is my daily driver and weekend enjoyment car. I don't track it and I don't plan to. I just want to rebuild it so that it can last a much longer time than another 3-1/2 years. :)

The weak link in the engine is the rods not pistons, although good to change pistons when doing rods anyways. Crank is good for a ton of power.
FBO + E85 +69-70mm pulley is 295-300whp on a dynojet.
Whatever you do don’t lower CR on supercharged engines especially if you have E85. You will max out the blowers long before lower CR would be beneficial.

Really the stock block should hold up just fine to max effort sprintex build. And if it eventually goes, a replacement stock block would be cheaper than a built block.

If going for a built block then switch to the Sprintex 335 or another FI and go for 400whp.

Once you have the engine open to replace everything else with forged, it would be a waste to leave to stock cast pistons. The cost of pistons isn't prohibitive.

Do it once and do it well, then seal the engine (you're already building!) back up with peace of mind knowing you've done it right.

.. if goal is for massive boost which will be regularly used. If car is just daily and not pushed that much and one frequently drives relatively short distances, there are pros to non-forged pistons, eg. in relation to less differing thermal expansion, so less wear when engine is not yet heated up.

Are there rods that work with the stock piston?