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Hi. I’m about to pull the trigger on a set of cp Carrillo pistons for my m30b34 in prep for a turbo in the future. The only thing is off the shelf I can get a set with all the oem specs except the compression ratio which would be 8.5:1 my understanding is stock is 8:1. Would I still be able to use these pistons before I turbo and on stock tune? I’m not financially ready to turbo quote yet but I would like to drive my car around in the spring. Thank you all.

Welcome to the group Walter!

You neglected to mention exactly what engine you have. I'm guessing a US spec 3.5 in a 535i. Assuming that, yes, the stock engine management system will work just fine. I'd expect a modest bump in power, 5hp maybe? Not dramatic, but enough to notice. Emissions might be slightly higher and if you have to pass Nox as in especially California, but it shouldn't send it thru the roof or anything.

If I may offer an opinion, your money would be better spent elsewhere. The stock pistons are not going to present any sort of obstacle. Put that money toward engine management or turbo parts. You can make 400+ rwhp on stock M30 parts with no compromise of reliability.

For what those pistons cost you could get everything you need to get the car running on Megasquirt. Motronic is the main obstacle to forced induction, once you have that out of the way it is pretty simple going forward.