choosing pistons

[horsepower addiction]

pretty much all the top piston manufacturers have solid products. Where people make mistakes is choosing the material. can someone explain to me why 2618 is a better choice than 4032 or vice-versa?

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[Cory S]

“Better” isn’t really a correct term to use when comparing 2618’s and 4032’s.

Relative to 2618, 4032 is a less ductile alloy, making it less forgiving when used in motorsport applications with high cylinder pressures. 2618 is a low-silicon, high-expansion alloy that is used for high boost and extreme-duty racing applications.

MOST aftermarket short blocks (LM, RPG, JPC etc) are setup with 2618’s. The Ford Aluminator uses 4032 Mahle slugs.

If you rattle (detonate) with a 4032 piston, it will shatter much sooner than a 2618 piston. With 2618’s, there’s a better chance of a head gasket failing before the piston fails.

4032’s are quieter due to a little tighter PTW clearance recommended. They generally will last longer when used as a high mileage street car. Example: 8-10 years or 80-100K miles. Or longer…. Power generated during this time can also alter the lifespan as well.

A proper machined cylinder with a 2618
Piston, can still be almost silent but generally will have some skirt wear after less abuse/mileage than a prepped 4032 piston/bore setup.

 

[Timbuck]

another option mahle M142P. It gives a bit of both worlds with more OEM tighter tolerances less expansion and still ductile enough for punishment and 100,000 + mile testing.
https://www.us.mahle.com/media/usa/motorsports/ford-modular-5-0-coyote-voodoo-webpage-2.pdf

 

[Optimum Performance]

pretty much all the top piston manufacturers have solid products. Where people make mistakes is choosing the material. can someone explain to me why 2618 is a better choice than 4032 or vice-versa?

What is the intended application? Power range etc? Off the shelf pistons are just that, a compromise. They may be fine for many applications but people tend to assume it works across the board. It does not, even in an N/A application. The proper way to purchase a piston is to order it for the finished bore, not try to make the bore match a piston. But again, this depends on the intended power levels and rpm.

 

[engineermike]

In the Mahle Catalog, just looking at the piston materials and clearance:

M142P spec is 0.0006 - 0.0014 clearance
2618 spec is 0.0025 - .0033 clearance, though this varies some depending on which piston.

That's a huge difference. For comparison, the GT500 spec is .001-.002, leading me to believe they are likely the M142P, 4032 , or similar. Another comparison is stock Coyote at -0.0002-0.0011. Yes, that'd be interference but that's with the grafal coating.

Another interesting note is that Mahle started offering a drop-in Gen3 piston that is 10.4/1 compression. This is exactly what compression ratio I would target on a supercharged Gen3 build.

 

[horsepower addiction]

So the only benefit to 2618 is ductility. It can take more detonation than any other but it’s softer and expands 15% more than m142p. So 2618 wears out much faster, I wonder if people know that they are expected to change 2618s every 30,000 miles or less. If you have a race engine that you tear down regularly and make big numbers 2618 is perfect for you. But if you want to build one engine and have it last 100,000 miles 4032/m142p seems to be the better choice.
If stock pistons are holding 1000+ as long as there’s no detonation. How much more can m142p pistons hold over stocks. At what point is 2618 needed. Is 2618 able to hold a little more than m142p or is it a significant difference
Mahle drop in pistons appear to be 2618.

 

[Timbuck]

I don’t know the answer , but your logic 100% matches is why I went with M142p. They will easy do 1000+ , I only want 750 , 800 on an every day driver. Give me OEM type warm up times etc and Longevity.
through my research I felt it was a good all round option for a street car.
if You compare the “ physical and mechanical property’s“ of the alloys gives you a good representation of there differences. They are different , but in my eye’s the mechanical difference in overall strength wasn’t massive , maybe 10% if you could put a number on it.
so many factors go into the over all mechanical ability of an alloy.

google the different properties to get an idea of there meaning.

 

[HKusp]

I'm going to test that theory with my car. I have Mahle 2618's with a piston to wall clearance of .0036. I daily it about 20k miles a year.

 

[Cory S]

I'm going to test that theory with my car. I have Mahle 2618's with a piston to wall clearance of .0036. I daily it about 20k miles a year.

I’ll give you a call in a couple years for an update.

 

[HKusp]

It better work after all this bullshit.

 

[illtal]

In the Mahle Catalog, just looking at the piston materials and clearance:

M142P spec is 0.0006 - 0.0014 clearance
2618 spec is 0.0025 - .0033 clearance, though this varies some depending on which piston.

That's a huge difference. For comparison, the GT500 spec is .001-.002, leading me to believe they are likely the M142P, 4032 , or similar. Another comparison is stock Coyote at -0.0002-0.0011. Yes, that'd be interference but that's with the grafal coating.

Another interesting note is that Mahle started offering a drop-in Gen3 piston that is 10.4/1 compression. This is exactly what compression ratio I would target on a supercharged Gen3 build.

The mahle option is interesting since it is still 2618 alloy. That 10.4 CR is calculated with a .040 head gasket and a -.015 deck height. Should be a really good setup for those looking for what would be "middling" levels of boost.

I would be interested in putting those in my "spare" block whenever I get my car back.

 

[engineermike]

@illtal I probably wouldn’t have built my [spare] predator short block if these pistons had been available a year ago. Rule of thumb is that gdi allows about one compression number higher than port. As compared to the predator, that means 10.5/1 would be similar as far as knock resistance goes. I believe it’s really the sweet spot on a boosted gen3.

 

[illtal]

@illtal I probably wouldn’t have built my [spare] predator short block if these pistons had been available a year ago. Rule of thumb is that gdi allows about one compression number higher than port. As compared to the predator, that means 10.5/1 would be similar as far as knock resistance goes. I believe it’s really the sweet spot on a boosted gen3.

Would it suffice to say something in the 10.5 range would be allow significantly better detonation resistance? I think so as well, but the argument that it's better to run a lower boost number with a higher CR to keep more TQ is troubling to be because most of us are dependent on 93 octane, which could be very hit or miss. I do not trust it so I use water/meth.

A lower CR In some configurations lead to a higher EGT which could aid in turbo boost response. It would take lot of testing to confirm but that research is out there (I suspect there is an optimal configuration). Lots of turbo setups don't run it the max efficiency ranges because of the octane limitations.

I take it your Predator block is a 9.5 CR? I thought you had it stripped down, should have upgraded them man.

 

[HKusp]

I dropped my compression down to 11:1 with a gasket height of .039. The vendor didn't offer the option for a 10.4:1 when I ordered my kit.

 

[illtal]

I dropped my compression down to 11:1 with a gasket height of .039. The vendor didn't offer the option for a 10.4:1 when I ordered my kit.

Stock Gen 3 setup?
I guess I should calculate what mine actually is with my head gasket.

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