2618 vs. 4032?

[Casper393W]

What Walter said.

Tell Randy what you're doing and give him your finish bore size. Have him put the clearance in the piston. Takasawas get the finished sizes within about .0001. It's not an issue.

4032 is priced and marketed as a "lower quality" composition. It is not. Nor are they less expensive to make. Actually they are more expensive to make. That nonsense is all marketing. Nor can you run them any tighter, really. You can run 2618 at .0025 (4.030 bore) if they cut the skirts properly.

My own opinion is that pretty much anything that will destroy a 2618 piston will kill a 4032...given an equal layout....and I've seen racers turn both alloys into BBs.....bless their hearts.

Thanks for posting this.... I have always been told to run a 2618 looser in the bore compared to 4032... If you don't mind me asking what would be the difference in the skirts to run the 2618 tighter? I have seen many 4032 pistons scuffed in 03,04 Cobras due to "in my opinion" cylinder thickness in cylinders 7 and 8 and the coolant flow causing higher heat buildup in those cylinder.

I am a fan of the 4032 Mahle pistons... I have seen serious power made on those pistons.. 1000+ I told them if you ever rattle them kiss them goodnight! But it never happened

I don't mind you asking at all, and I wouldn't mind answering, but skirt design is a frightfully complicated subject. It used to be a world of cam and taper, and now it's a world of shapes. Even the thickness of the skirt comes into play. The change in skirt designs is like when we went from black and white to color tv. Bonanza entered a completely different universe.

The skirt I used came from the Ford Technology transfer program. We ran 2618 as tight as .0025. Scuffing was never an issue.

I'm not a Mahle fan. The pistons are fine, I'm just weary of the major corporations driving out the smaller manufacturers and engine builders that built the hobby, so I try to deal with the mom and pop operations and steer clear of the behemoths.

Thank you sir, I need to rephrase what I was saying about the Mahle pistons... I like the design... Like you said companies such as Mahle do make it extremely hard for the small business owner... I know I have brought this up on another thread and I took a beating over it... When I am sourcing parts for engine builds I always try my very best to buy from American companies and to break it down even more I have a few vendors that I buy from that are "Mom and Pop" shops... They provide me a quality product not always the cheapest but I know at the end of the day they will make things good if I run into problems.....

Andy

[Cougar5.0]

I don't mind you asking at all, and I wouldn't mind answering, but skirt design is a frightfully complicated subject. It used to be a world of cam and taper, and now it's a world of shapes. Even the thickness of the skirt comes into play. The change in skirt designs is like when we went from black and white to color tv. Bonanza entered a completely different universe.

The skirt I used came from the Ford Technology transfer program. We ran 2618 as tight as .0025. Scuffing was never an issue.

...

I can confirm this. I ran a set of your Probe pistons that tight (0.0028" - 0.0025" - perhaps even a tenth or two tighter on a couple) in a supercharged SBF application and saw no scuffing after ~10k miles of street driving and drag racing. When a rod bearing took out the engine, the pistons were clean enough to sell.

[Frankshaft]

So then what's the issue? I have lost a good portion of the last summer trying to decide on Pistons for my Polaris CFI 800. The arguments are, new, updated stock cast pistons, no, wiseco forged, no, wossner forged. I have decided on Wossner forged because they are made from 4032 alloy, vs 2618 for the wiseco. The cast factory are hyperuetectic. So, I thought since the Wossner forged are literally 60 grams each lighter, and forged from 4032 lower expansion high silicone forged material, it would be a better choice than wiseco 2618 low silicone higher expansion material, more sensitive to heat cycling. Am I wrong?

[pdq67]

I am going to come out with a little history here so please bear with me!

Off the topic, I don't know, you be the judge.

Back when I made my old junk301 out of well JUNK PARTS, my pistons were a set of W/JCW 1/8" over, 1/8" tall, 1/2 round 290/315 Hp 283 stock type steel strutted cast pistons! Way later I found out from SOMEPLACE that up to like 300 to 325 Hp, these pistons would hold up fine and mine did!

And many a 7500 rpm blast on them. Now I do know that these old stock cast pistons did break their skirts off because of the dammed near 1/2 round oil drain back grooves, one on each side, instead of a bunch of oil drain back holes..

Mark,

What was the alloy of the old style forged pistons that had like .006" to .007" skirt clearance on them OR was it because of the crude skirt design from back then?

pdq67

[Mark O'Neal]

So then what's the issue? I have lost a good portion of the last summer trying to decide on Pistons for my Polaris CFI 800. The arguments are, new, updated stock cast pistons, no, wiseco forged, no, wossner forged. I have decided on Wossner forged because they are made from 4032 alloy, vs 2618 for the wiseco. The cast factory are hyperuetectic. So, I thought since the Wossner forged are literally 60 grams each lighter, and forged from 4032 lower expansion high silicone forged material, it would be a better choice than wiseco 2618 low silicone higher expansion material, more sensitive to heat cycling. Am I wrong?

Either would be fine, as far as the material goes. I'd certainly take the weight savings.

Other than that I know nothing about snow mobiles.

[Mark O'Neal]

I am going to come out with a little history here so please bear with me!

Off the topic, I don't know, you be the judge.

Back when I made my old junk301 out of well JUNK PARTS, my pistons were a set of W/JCW 1/8" over, 1/8" tall, 1/2 round 290/315 Hp 283 stock type steel strutted cast pistons! Way later I found out from SOMEPLACE that up to like 300 to 325 Hp, these pistons would hold up fine and mine did!

And many a 7500 rpm blast on them. Now I do know that these old stock cast pistons did break their skirts off because of the dammed near 1/2 round oil drain back grooves, one on each side, instead of a bunch of oil drain back holes..

Mark,

What was the alloy of the old style forged pistons that had like .006" to .007" skirt clearance on them OR was it because of the crude skirt design from back then?

pdq67

2618 it what you're thinking of, and the standard was .008. we tightened them up a whole .001 for 4032. You could run the 2618 at .005, just don't shut the car off when you got to Dunkin' Donuts.

They were very sophisticated...considering the skirts were done on an old cam grinder.

Sometimes I think about the pistons we made in the early 80s and fell kinda guilty......

[My427stang]

Krooser - Just want to make sure it's clear, there are no hyper choices in your selection from Randy. 2618 and 4032 are both forged pistons

The guys have said it in a few different ways, but I just wanted to make it crystal clear.

Personally, I think either will live, but without boring, both could be noisy when cold, but the 2618 will grow more and be slightly stronger. The real issue comes with how straight your bore is now. Loose is one thing, Randy can likely work a piston for you, but if the bores aren't true, best you can do is run loose and expect piston and ring wear

[piston guy]

The confusion"to me" comes from the fact that "most" cast pistons are 'high silicon" content aluminum. Forgings are made from 4032 alloy bar stock preheated and "smashed" into shape in the forging process. Cast pistons are poured from molten aluminum and dependent on what actually gets melted. Besides their obvious lesser density , the material "could" be altered so to speak especially "if" recycled material was in the melt.
4032 has it's place. It obviously is not as ductile as 2618 is. It is strong but more "glass like" in structure so cylinder pressure spikes , high inertia , and mechanical impact can damage it quickly. The actual engine design can play a role in which alloy to use as well. The LS Chevy for example, is very easy on parts while making lots of HP even with power adders.
Piston to wall is another subject altogether. With the advent of CNC turned skirts, manufacturers have their own shapes and also where they are checked. This can cause confusion when quoting piston to wall clearance specs OR WORSE when using "general knowledge". Yes 4032 does have a lower expansion rate than 2618 but the different skirt shapes and gauge points used in the industry make it imperative to go by the manufacturer's recommendation rather than whats "always been done".
2618 is the alloy of choice for high power applications and with good reason. From Top fuel to a Briggs and Stratton , it gets the job done.

[Frankshaft]

So, then there is or isn't a difference in temperature sensitivity and thermal expansion differences? Between 4032 and 2618. I know 2618 is stronger, but I am basing my piston selection for my Snowmobile because they are much less forgiving than a 4 stroke, and the wisecos definitely have more of a reputation for seizure compared to Wossner forged, and especially compared to stock, from cold sieze, and running warm in general.

[PackardV8]

So, then there is or isn't a difference in temperature sensitivity and thermal expansion differences? Between 4032 and 2618. I know 2618 is stronger, but I am basing my piston selection for my Snowmobile because they are much less forgiving than a 4 stroke, and the wisecos definitely have more of a reputation for seizure compared to Wossner forged, and especially compared to stock, from cold sieze, and running warm in general.

I covered specifically, exactly this question early on in this thread:

For the toughest pistons, 2618 is a low-silicon, high-expansion alloy that is used for extreme-duty racing applications. Due to its high-expansion characteristic, this alloy is engineered with additional piston to bore clearance. 2618 is a more ductile alloy with higher resistance to detonation. The forgiving characteristics allow for the most extreme conditions, but longevity is eventually negotiated after many heat cycles.

forged from 4032 lower expansion high silicone forged material, it would be a better choice than wiseco 2618 low silicone higher expansion material, more sensitive to heat cycling. Am I wrong?

No, that's a reasonable choice. Key question; does your engine detonate? If yes, theoretically, 2618 will live a bit longer than 4032. As to sensitivity to heat cycling, how many full-temperature cycles does a racing snowmobile see in a lifetime?

Comparing a 2618 Wiseco to a 40 gram lighter 4032 Wossner certainly isn't apples-to-apples, but also doesn't take into consideration skirt design and finishing. Skirt design determines wall-clearance and affects sensitivity to seizure on two-strokes equally or more so than material. So no, there's not a hard-and-fast rule for piston-to-wall-clearance-per-inch-of-bore-diameter for either alloy. The manufacturer's recommendation has to take into consideration bore diameter, piston height, fuels/boost, RPM, duty cycle, 2-stroke vs. 4-stroke, air-cooled vs. water cooled, among others.

And yes, today's CNC skirt finishing has completely changed the old understandings of what works best. That is when there's any skirt remaining.

[Frankshaft]

So, then there is or isn't a difference in temperature sensitivity and thermal expansion differences? Between 4032 and 2618. I know 2618 is stronger, but I am basing my piston selection for my Snowmobile because they are much less forgiving than a 4 stroke, and the wisecos definitely have more of a reputation for seizure compared to Wossner forged, and especially compared to stock, from cold sieze, and running warm in general.

I covered specifically, exactly this question early on in this thread:

For the toughest pistons, 2618 is a low-silicon, high-expansion alloy that is used for extreme-duty racing applications. Due to its high-expansion characteristic, this alloy is engineered with additional piston to bore clearance. 2618 is a more ductile alloy with higher resistance to detonation. The forgiving characteristics allow for the most extreme conditions, but longevity is eventually negotiated after many heat cycles.

forged from 4032 lower expansion high silicone forged material, it would be a better choice than wiseco 2618 low silicone higher expansion material, more sensitive to heat cycling. Am I wrong?

No, that's a reasonable choice. Key question; does your engine detonate? If yes, theoretically, 2618 will live a bit longer than 4032. As to sensitivity to heat cycling, how many full-temperature cycles does a racing snowmobile see in a lifetime?

Comparing a 2618 Wiseco to a 40 gram lighter 4032 Wossner certainly isn't apples-to-apples, but also doesn't take into consideration skirt design and finishing. Skirt design determines wall-clearance and affects sensitivity to seizure on two-strokes equally or more so than material. So no, there's not a hard-and-fast rule for piston-to-wall-clearance-per-inch-of-bore-diameter for either alloy. The manufacturer's recommendation has to take into consideration bore diameter, piston height, fuels/boost, RPM, duty cycle, 2-stroke vs. 4-stroke, air-cooled vs. water cooled, among others.

And yes, today's CNC skirt finishing has completely changed the old understandings of what works best. That is when there's any skirt remaining.

Thanks for the reply. I went back and read what you wrote about the difference between the 2 alloys, and that's what I have always thought about them. That's why originally I didn't want to run wisecos in it. It's not a "race" machine, but it will be rode hard. Trail miles, in some cases, 150+ miles away from where I started, in the middle of nowhere. It's not fun dealing with a broken machine. When I found out Wossners were made from 4032, I was happy. They are $100 each, vs ,$225 each for an oem replacement. I thought it was a no brainier. Forged 4032 is still stronger than a cast piston, and being 60 grams each lighter, is great. But then there was some contradiction about the alloys, which is where my questions came from.

[piston guy]

To add just a touch to Jack's reply , the piston can handle a tremendous amount of heat cycles as long as it isn't OVERHEATED. There are charts available that show a time versus temperature on the annealing of aluminum alloys. As little as 100*s increase in crown temperature can cut piston life IN HALF in the elevated temperatures. Extreme over heating ( I.E. Nitro cars) can "kill " pistons in seconds as most of us have seen. Heat management is an important part of overall piston design. Too thin and it melts or cracks, too thick and it's a brick that breaks parts. The idea I have is always to make the piston outlive the bore size/quality. Doesn't always happen.

[Krooser]

Krooser - Just want to make sure it's clear, there are no hyper choices in your selection from Randy. 2618 and 4032 are both forged pistons

The guys have said it in a few different ways, but I just wanted to make it crystal clear.

Personally, I think either will live, but without boring, both could be noisy when cold, but the 2618 will grow more and be slightly stronger. The real issue comes with how straight your bore is now. Loose is one thing, Randy can likely work a piston for you, but if the bores aren't true, best you can do is run loose and expect piston and ring wear

Having never paid much attention to hyper slugs I guess i didn't realize they are all cast. Must be why the price is so low.

I know all of the Auto Tec line are forged...

I'm going to send the block to the machine shop to have him measure everthing to be certain what I have but I don't expect any surprises. All the work was done at a quality shop... might even make the trip and take it back to that builder. They recently redid the rods from this motor for me.

Lots of good info on this thread guys...thanks.

[Frankshaft]

Thread is sorta dead, but in my example above between wiseco and wossner for my Snowmobile, I mentioned the Wossner Pistons being 60 grams lighter each. The wisecos are in that range lighter also, as compared to stock. Wiseco 2618, Wossner 4032. There was some confusion about the weights between the forged aftermarket Pistons.