Forged Pistons in a Brand-New N54 Block – Measurements?

[6ixInline]

Hey everyone,
I recently got a brand-new engine block and I’m looking to install forged pistons with a 9.5:1 compression ratio. Before I place an order, I want to make sure I get the right clearance.
From what I've seen, the OEM pistons measure around 83.967 mm, but most aftermarket forged pistons I found are 84mm, which seems a bit tight for a new block (my cylinder bores measure 84.00 - 84.01 mm).
Has anyone here installed forged pistons in a brand-new N54 block and what piston size did you use?

 

[shushikiary]

Even if it's a new block you need to hone each cylinder to the piston manufacture's spec for that piston. The pistons may have some variance, and usually you want to be within 0.5 thousands of an inch the entire length of the bore. Most forged pistons need 4 thou clearance in diamater from the widest part of the piston (they are oval not round).

So you need to read the piston's spec sheet, measure each piston in the CORRECT spot, then hone to that diameter. This is because forged pistons expand more than the stock hypereutectic pistons, so they need more clearance.

 

[6ixInline]

The reason I bought a brand-new block is that I couldn’t find a shop in Europe capable of honing the block to BMW’s specifications—none of them had a profilometer to measure surface finish properly.
If I buy a set of 4032 forged pistons in 84.00 STD (A) (83.96-83.97 mm) and after measuring, I get 0.002” (2 thousandths of an inch) clearance, can I get away without honing? Or would honing still be necessary.
I also measured the taper, and it's very small
Thanks for your input!

 

[shushikiary]

No, if you do not hone the engine, you may seize a piston, you ALWAYS hone. Sorry to be the bearer of bad news, but the path you have taken is not feasible. This is why the block was sold with the bores slightly undersized, specifically so you had enough material to hone to size. You will need to ship the block and pistons to a location that can hone it.

You can choose not to, you are just playing with fire and may literally seize a piston in a cylinder. Even if you got stock pistons.

 

[Bimmerfab]

I used to think the forums were a helpful supportive place not filled with contradictions. Wow am I glad I haven't been on this site for years LOL

 

[langsbr]

Curious why and where you are looking at 4032 pistons. Most all brand name forged pistons for the N54 are going to be 2618, including Mahle, Manley, JE and others.

The only 4032s I've seen are the chinese ones like MaxSpeedingRods and other Ali marketplace ones. If you spent the money on a brand new block, I would urge you to spend the slight bit more that 2618s cost. 4032s are going to be brittle vs the 2618s and be much better suited to the high boost situations the N54 sees.

 

[JohnDaviz]

I used to think the forums were a helpful supportive place not filled with contradictions. Wow am I glad I haven't been on this site for years LOL

would be nice if you continue with that behavior

 

[6ixInline]

Curious why and where you are looking at 4032 pistons. Most all brand name forged pistons for the N54 are going to be 2618, including Mahle, Manley, JE and others.

The only 4032s I've seen are the chinese ones like MaxSpeedingRods and other Ali marketplace ones. If you spent the money on a brand new block, I would urge you to spend the slight bit more that 2618s cost. 4032s are going to be brittle vs the 2618s and be much better suited to the high boost situations the N54 sees.

I don’t have the necessary clearance for 2618 pistons, and they also come with thin 1mm steel rings, which don’t retain oil well. That would require a special honing process with deeper crosshatch grooves to ensure proper oil retention.

At this point, I think I’ll just go with OEM pistons since they are designed to work with the factory bore and don’t require additional honing.

 

[langsbr]

Have you been able to find 9.5:1 OEM pistons?

 

[6ixInline]

Have you been able to find 9.5:1 OEM pistons?

I haven't been able to find, but I do have a 1.5mm thick head gasket. However, I don't think it will make a significant difference in lowering the compression. I'm still searching to see if anyone makes custom pistons with the specs I need.

 

[langsbr]

I would think that the vast majority of built engines even in the US do not have machine shops all using profilometers to get specific RA/RK and the engines all perform properly. Is it just the profilometer requirement that is causing you an issue with properly boring/honing the block? Also, if you are going to use 9.5:1 aftermarket forged pistons, I'd expect BMW specs to be the last thing you'd need to be concerned with. You wouldn't use BMW specs on the ring gap and piston to wall clearance using them, so why be so concerned with the surface finish. I'd say in the grand scheme of building the motor, the surface finish is WAY down the line on things to be overly concerned with.

 

[6ixInline]

I don't know, I just like how the factory honing looks, and I figured it would work best with OEM-style rings. I didn't want to go through the hassle of getting a torque plate and sending the block to a shop for machining.
The problem I have with machine shops is that each one does things their own way. If I had gone to 10 different shops, I would have ended up with 10 different honing methods. I've seen a lot of people sell their cars right after building the engine, either because they weren't happy with how it ran or they were afraid to push it too hard. So, I decided to stick with BMW specs for components that aren't heavily affected by increased power.Of course, when it comes to compression and ring gap, I'm not following BMW specs, since the engine is so knock-limited.

 

[Bimmerfab]

30psi on a G35 1050 on kingtecs for 10k miles. 4032 material. Haven't cracked in half like the experts on the forums will tell you. Do some research of your own vs 2618 vs 4032 materials. Summit racing has a couple good videos of explaining how each materials works.4032 if under 1000whp will be perfect. supertech sells a 4032 piston as well

 

[Bimmerfab]

 

[6ixInline]

I had the same impression that 4032 can handle a decent amount of power. If something is going to go wrong, it can happen with 2618 as well-maybe not right away, but eventually. Even my old engine ran pretty good on pump gas and a bit of meth, 28-30 psi for around 30k miles before this happened. I have no idea what caused it.

 

[langsbr]

30psi on a G35 1050 on kingtecs for 10k miles. 4032 material. Haven't cracked in half like the experts on the forums will tell you. Do some research of your own vs 2618 vs 4032 materials. Summit racing has a couple good videos of explaining how each materials works.4032 if under 1000whp will be perfect. supertech sells a 4032 piston as well

I'm not an expert (but I did stay at a Holiday Inn last night. - kidding, who the hell stays there now), but I have not found ANY reputable piston manufacturers that offer a 4032 alloy piston for the N54. I figured if they were 'good enough' then all reputable brands would offer them. Granted, it could simply be a case of low production volume, so why bother. Supertech, I'm on the fence if I'd call their pistons top of the line, or them a reputable piston maker rather than just a reseller. I see they no longer offer N54 pistons and most of their B58 options are 2618, so perhaps they learned some.

In the video linked they said for 750-800HP in a V8 application is about the limit on 4032 before you should move to 2618. How little power are you looking to make on the N54? That's 100HP per piston which is 600 for the N54 - the stock pistons can do that for a while, above that it's playing with fire.

If nothing else, it's cheap insurance to use a 2618 piston. These motors are knock sensitive as it is, and that gets exacerbated when running PI at high power levels.

 

[Cruizinmax]

I had the same impression that 4032 can handle a decent amount of power. If something is going to go wrong, it can happen with 2618 as well-maybe not right away, but eventually. Even my old engine ran pretty good on pump gas and a bit of meth, 28-30 psi for around 30k miles before this happened. I have no idea what caused it.

From that photo, it looks like the engine ingested some foreign debris. Shaped like spark plug ceramic or something?

 

[6ixInline]

From that photo, it looks like the engine ingested some foreign debris. Shaped like spark plug ceramic or something?

It wasn't caused by the spark plugs. I also found these small metallic beads in the secondary cats, and they seem to be aluminum.

 

[wheela]

I agree, it does look like something got ingested. Does the cylinder head have marks like that too?

 

[6ixInline]

I agree, it does look like something got ingested. Does the cylinder head have marks like that too?

Yes, the cylinder head has the same marks as well.