M5x Frankenstein Build - Guidance would be helpful

[NORBY]

Hi All,

This is my first go at a full engine build, previously I have really only worked on maintenance items - so there is lots of learning to be done.

Goal: M5x Turbo, 3.0L, S50 Cams (Essentially an S50B30 US + T), Reliable, 'New'

What I have so far: Complete M52B25 Single Vanos, M50 Iron block with no rotating assembly, M54B30 Block with the rotating assembly

Being an Australia anything with an "S" in front of the engine code is really expensive, and doesn't really fit with my build, so I have been slowly collecting parts to build-up this combination of bits to make my ideal m5x engine, looking to make something around 350hp reliably


So my first questions:

• I see a lot about people saying you should balance the crank and pistons, given this is all coming out of the M54b30 which was in good condition, am I just throwing money away? Or do to pistons/crank get 'out of balance' over time?
• I did some reading about replacing the rings to the non-factory M54 ones because they leak oil, is this a thing? Are there special considerations I should make considering I want to turbo the car (I have read to have the rings gapped looser)
• If I am just focusing on the rotating assembly at the moment, what else should I replace as part of the process? I want as much as the build to be new and done properly as possible, but I also don't want to replace things that don't need it.
• Any tips for the bottom end assembly/traps for new players?

[JRHemmen]

If you're trying to keep costs down, stick to things that will be a bear to access once it's all together. Think pilot bearing, water seals, etc. Some leaks can be easily fixed as they're discovered, while others could require pulling the engine out again. I've kept a spreadsheet of parts that I've ordered and can PM you a list of what I ordered to replace every single wear item on my engine (besides anything related to the rotating assembly) if you'd like. It will differ a bit since I'm running an OBDI converted M52, but it could be a good place to start.

[Metallated]

I went nearly the exact same route (build linked in my bio)...
I didn't balance it, and yes it is a bad idea to use the carbon coated m54 rings. I reused the old m50 rings, even though a couple thought this was a bad idea.
I don't know if my build is up to your standards of "done properly". I did it on a tight budget, but in the end it runs great and a recent leakdown test shows everything turned out solid.
I could have just gotten lucky!

[NORBY]

Awesome, thanks guys! I will do a little more digging in your threads to get a better understanding and maybe some more specific questions will come up. I'm considering just selling the M54B30 rotating assembly and buying some forged connecting rods and pistons. Ultimately more expensive, but probably better for my sanity

[pazi88]

Balancing that is bit of waste of money. Problem in the b30 crank isn't lack of balancing, it's just the long stroke which is causing vibration problems. Throwing in ATI damper helps lot more to the vibration problem problem than balancing does.

350hp is such low number that you can basically do that with any bone stock m5x if it's not totally clapped out. No need to worry about getting forged internals etc. with that HP level. Especially if you use e85, the 350hp will be walk in the park. But still replacing rings, bearings etc. for these engine costs next to nothing. So if the engine is apart, there is no really reason not to do that. The m54 rings can cause oil burning issues, but that's mainly problem on higher mileage ones with "long life" oil changes. Just change oils often (which you should do anyways with turbo engine) and the new m54 rings will do just fine. The m50 rings are wider, so you would need to machine the m54 pistons to fit those.