Technical 4032 vs 2618 forged piston alloy?

IQraceworks

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I’m getting ready to bite the bullet and order my forged piston for my N54 build. I was dead set on ordering the Mahle pistons, but then I noticed that they are made out of 2618 alloy, when most all other brands of N54 pistons (JE, AMP44, etc) are made out of 4032 alloy.

From the little research I’ve done, it sounds like the 2618 is stronger, but expands about 15% more when hot than the 4032 allow, so you need to set up the piston to bore clearance to compensate for that. So instead of the typical .0015” - .0020” piston to cylinder wall clearances used on the 4032 pistons, the 2618 pistons need a larger .0025”-0.035” clearance. When everything is hot and warmed up, the final clearance will be the same regardless of if the pistons are 4032 or 2618.

So….my question is, when the larger clearances on the Mahle 2618 pistons…..is that going to cause lots of piston noise on startup? If so, is that enough to cause false knock sensor codes?

From what I’ve seen, the Mahle pistons seem pretty popular….and I’ve never heard of anyone having issues with them in the N54 motors, but I thought I would double check. Maybe I’m just overthinking things. I find it stranger that they are on the only company I could find making N54 pistons out of 2618 alloy, when everyone else uses 4032.

Any information or feedback would be great!! Thanks
 
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JohnDaviz

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you get it wrong with most use 4032. This is just what you think to see.


Read thorough and you will know yourself what to do. As i said on Facebook. The Mahle ones are a great choice.
 
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IQraceworks

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Thanks, but that JE article pretty much sums up what I had initially thought…

Everything I’m reading basically says for a street car that you are going to be putting a lot of mines on, and want long life and a strong piston, and quite cold startups..….use 4032, for a race car that isn’t going to get driven tens of thousands of miles, and you don’t care about cold start noise, go with 2618 because it’s the strongest alloy you can get.

Which leads me back to my original question…..why does Mahle make their N54 PowerPack forged pistons from 2618, and will they last in a street car that’s going to see lots of miles? Does their coating they put on the pistons help increase life?

I’m just worried about throwing the Mahle 2618 pistons in my motor, and then in a year when I have 10,000+ miles on the thing…it’s sucking down all kinds of oil and rattling like crazy on cold starts.

That being said…..lots of reputable 335i/N54 aftermarket parts vendors sell the Mahle Power Pack 2618 forged pistons…..so they can’t be all that bad. Also being said…most guys who are throwing forged internals in their N54 are probably using them as weekend/track cars, not daily drivers that see lots of miles.
 
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JohnDaviz

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so trust what you understood from the article and make you own choice.

You will never find the definite answer from random ppl on FB or a Forum.

For me. Mahle is the OE for the N54 (and a shit ton more OEMs) and made just a better forged version with their HUGE knowledge. My perfect piston. The stronger OE design from a company that is as big or bigger as all aftermarket piston companies together.
 
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IQraceworks

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As far as I know.....no OEM's use a 2618 alloy forged piston, they are all 4032 alloy. Because (like the article above says), the 2618 allow does not wear as good or last as long, and is nosy on cold startup. It's designed as a "race" piston.
 
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JohnDaviz

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so i guess you made your decision for 4032 pistons. Great! Good luck with your project!
 
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wheela

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That article mentions they can do an anodized hardcoat option on the 2816 pistons to increase wear resistance. I wonder what the downside to the anodization is? It seems like an anodized hardcoat would be a no-brainer, not sure why it's only an option and not standard🤷‍♂️?
 

fmorelli

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So….my question is, when the larger clearances on the Mahle 2618 pistons…..is that going to cause lots of piston noise on startup? If so, is that enough to cause false knock sensor codes?
You asked for input. I would think if piston noise on startup is the first issue for you ... honestly I can't imagine this is your first issue ... might be worth reframing the question (if it is my suggestion would be, leave your motor alone lol ... but you knew I was going there).

As for false knocks on sensor codes; I'm sure you are not speaking on startup, but could piston slap cause false knock issues during operation? You mean before the material warms up? When specifically do you have this concern - at full temp operation? I suspect you know where I'm going with this line of questioning.
From what I’ve seen, the Mahle pistons seem pretty popular….and I’ve never heard of anyone having issues with them in the N54 motors, but I thought I would double check. Maybe I’m just overthinking things. I find it stranger that they are on the only company I could find making N54 pistons out of 2618 alloy, when everyone else uses 4032.

Any information or feedback would be great!! Thanks
I would flip this over and ask you a question. Mahle - who is arguably a powerhouse in this space - why did they decide to make the piston for this application in 2618 instead of 4032? When 4032 is often used by them for the Powerpak setups? I suspect there's a damn good reason since 1) they spend oodles of money developing their pistons, also in concert with BMW, and obviously through the Motorsport program. I would hazard that Mahle made some engineering decisions based on what they know about the N54, it's application, and its weaknesses.

Hope this helps the thinking process.
 

rev210

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Either material is going to work , the expansion difference is 15% of a really small amount. It's not like the piston is slapping around like crazy and blowing smoke , not even within many kms. Oh but, then if you are pushing big horsepower expect to be rebuilding , bearings/rings etc. on a far more frequent basis than a stock power engine.
2618 or 4032 either are going to do the job on really big horsepower. Ductile 2618 is maybe why Mahle might have picked it? The N54 bore doesn't like heat and cracks maybe as often as stock piston ring lands so the 2618 offers some advantages in thermal/ductile performance to assist ? Otherwise , you can't go wrong with 4032 and just good ring gaps and design ( 90% of the issue) . Neither are going to be cracking ring lands under a good tune and crazy power. They are both materials that are stupid strong.
For the 15% expansion you get around that in additional strength characteristics too.

Material Characteristics40322618
Tensile Strength55,000 psi64,000 psi
Yield Strength46,000 psi54,000 psi
Fatigue Endurance16,000 psi18,000 psi
Modulus of Elasticity11,400 psi10,400 psi
Melting Point990 – 1,060 F1,020 – 1,180 F
 

IQraceworks

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I reached out to Mahle for some more info...we'll see what they come back with. I'm guessing that the special coatings they use on their pistons will counteract some of the wear issues that non-coated 2618 pistons might have?

And yes...the main question I have is why did Mahle decide to go with 2618 on the N54 pistons when most all of their other pistons are 4032? They don't even offer them in 4032 as an option.
 

fmorelli

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I reached out to Mahle for some more info...we'll see what they come back with. I'm guessing that the special coatings they use on their pistons will counteract some of the wear issues that non-coated 2618 pistons might have?

And yes...the main question I have is why did Mahle decide to go with 2618 on the N54 pistons when most all of their other pistons are 4032? They don't even offer them in 4032 as an option.
Likely the answer lies in the benefits of 2618 against the limitations or weaknesses of the N54.
 

Griff500

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I reached out to Mahle for some more info...we'll see what they come back with. I'm guessing that the special coatings they use on their pistons will counteract some of the wear issues that non-coated 2618 pistons might have?

And yes...the main question I have is why did Mahle decide to go with 2618 on the N54 pistons when most all of their other pistons are 4032? They don't even offer them in 4032 as an option.

Very interested to hear their response.

I just expected Mahle to use 4032 for the reasons you’ve outlined and the market positioning of these pistons.
 

Ecosse_b58

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Jun 14, 2021
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Different engine but my input. I had the exact same thoughts when picking pistons for my built b58.

I wanted to go down the 4032 piston for its wear characteristics on a street motor but was very limited on manufacture choice availability I wanted to use a trusted piston manufacturer the only available in 4032 where supertech (iasa) and wossner.

When I spoke with multiple engine builders they said for a high compression (11.0:1) boosted motor 2618 is the only choice. They said a 4032 piston in this environment is only slightly stronger than the stock hypereutectic pistons and has the possibility of breaking like glass under detonation or high load and destroying a whole motor. And 4032 is more suited for na applications. Where as 2618 is more ductile and will flex and worst case crack.

I did my rounds before purchasing the pistons for my build and ended going with 2618 Cp Carrillo HD pistons with coated crowns and skirts. The skirt coating lets you run a slightly tighter Ptw clearance for the intended hp/ boost pressure.

I spoke with a local shop who uses mahle on most his evo builds and he said on boosted motors that aren’t pushing more than 100hp per cylinder he would fit powerpack pistons but if they want to run more than that he only uses powerpack plus which is the 2618 variant these are rated at 250hp per cylinder. And he has engines in circulation with over 50k miles on them that are daily driven using 2618. He said it all comes down to frequency of service intervals, quality fuel and letting the motor warm up to full operating temp before beating on it.
 

JohnDaviz

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Different engine but my input. I had the exact same thoughts when picking pistons for my built b58.

I wanted to go down the 4032 piston for its wear characteristics on a street motor but was very limited on manufacture choice availability I wanted to use a trusted piston manufacturer the only available in 4032 where supertech (iasa) and wossner.

When I spoke with multiple engine builders they said for a high compression (11.0:1) boosted motor 2618 is the only choice. They said a 4032 piston in this environment is only slightly stronger than the stock hypereutectic pistons and has the possibility of breaking like glass under detonation or high load and destroying a whole motor. And 4032 is more suited for na applications. Where as 2618 is more ductile and will flex and worst case crack.

I did my rounds before purchasing the pistons for my build and ended going with 2618 Cp Carrillo HD pistons with coated crowns and skirts. The skirt coating lets you run a slightly tighter Ptw clearance for the intended hp/ boost pressure.

I spoke with a local shop who uses mahle on most his evo builds and he said on boosted motors that aren’t pushing more than 100hp per cylinder he would fit powerpack pistons but if they want to run more than that he only uses powerpack plus which is the 2618 variant these are rated at 250hp per cylinder. And he has engines in circulation with over 50k miles on them that are daily driven using 2618. He said it all comes down to frequency of service intervals, quality fuel and letting the motor warm up to full operating temp before beating on it.

Where can we get more entertainment about your car while we are waiting for the Mahle Feedback :D
 

IQraceworks

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Just went ahead and ordered the Mahle 2618 alloy Powerpack forged pistons for my motor...also ordered Manley H-Beam forged rods. I figured that Mahle knows what they are doing, and if the only thing they offer the N54 pistons in are the 2618 alloy...they is a reason for it.

Wish me luck.
 

Ecosse_b58

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Jun 14, 2021
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Good choice 👍🏻 Make sure to follow the manufacturers instructions on piston to wall clearance and ring gap. They should be relatively quiet with minimal blow-by