2618 vs. 4032?

[Krooser]

I've never used any hyper pistons. I have heard the good and bad numerous times.

Now I'm about to order some SBM pistons for my dirt motor. Going to order from Randy @ RaceTec.

13 1/2-1 on alky. 7200 rpm. All cast iron heads/block. Oval track application.

Right now the old Ross pistons have .003 wall clearance. Too much for the hypers? I'm going to use a ball hone to regain the cross hatch. This engine has less than 25 laps on a freshen when a rod bearing seized due to lack of lubrication.

[rustbucket79]

Your post is confusing, you list 2 aluminum compositions commonly listed in forgings in your title, yet you talk about cast pistons in your thread.

What is the actual bore diameter?

[DCal]

Yeah I'm confused with this also but at 13.5 I would have a forged piston in there. Ask Randy about the material choice but 2618 would be mine.

[Krooser]

Your post is confusing, you list 2 aluminum compositions commonly listed in forgings in your title, yet you talk about cast pistons in your thread.

What is the actual bore diameter?

Cast iron bkock and heads. 4.030 bore.

Randy sez the 4032's will be fine... I'll accept that but my main concern is piston to bore clearance. I will not bore this block since it was recently done.

[Krooser]

xXXXXXXXXXX

[groberts101]

I've never used any hyper pistons. I have heard the good and bad numerous times.

Now I'm about to order some SBM pistons for my dirt motor. Going to order from Randy @ RaceTec.

13 1/2-1 on alky. 7200 rpm. All cast iron heads/block. Oval track application.

Right now the old Ross pistons have .003 wall clearance. Too much for the hypers? I'm going to use a ball hone to regain the cross hatch. This engine has less than 25 laps on a freshen when a rod bearing seized due to lack of lubrication.

Like the guys have already implied.. hypers are cast designs and far too brittle for that endurance type application. If the motor ever got too hot, leaned out, and/or the tune went away you'd likely pinch a ring or knock the ringlands out of those pistons before long. And yes .003 is too much clearance and defeats much of the benefit to running it in the first place.

I'd use a 2618 forging there too. If you want some of the benefits of the tighter fitting hyper designs you could have them line2line coated to build up the skirts a bit more. Could also coat the skirts on your old pistons to tighten up the clearance and reuse them after a rehone too.

[rustbucket79]

Right in Racetec's FAQ "we do not manufacture cast pistons"

Unless your block is over .001" from regular oversize (.021/.031/.041) clearance won't be an issue.

Custom piston? I don't see where they offer a stocking dome SBM piston.

[Walter R. Malik]

There is no "fits all" answer. It really depends upon what you want those pistons to do and act like.
2618 is slightly tougher and softer however, 4032 does not expand or change shape as much throughout a heat cycle and can fit tighter in the bore.
Either piston material can be sized for any finished bore size.

YOUR choice.

[PackardV8]

Krooser, you may be confusing hypereutectic cast pistons, which have high silicon content, with a forged 4032, which is a high-silicon, low-expansion alloy. As mentioned earlier, we don't beat hard on cast pistons.

There are distinct differences between forged pistons 4032 and 2618 alloys. The choice to use one over the other depends on the end use.

Pistons made from 4032 alloy can be installed with tighter piston to bore clearance, resulting in a tighter seal with less noise. 4032 is a more stable alloy, so it will retain characteristics such as ring groove integrity, for longer life cycle applications. Relative to 2618, 4032 is a less ductile alloy, making it less forgiving when used with boosted and/or nitrous applications.The majority of commonly used forgings are made with 4032 alloy and require no additional piston-bore clearance - .0025″-.0030″ clearance is usual.

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.

[Mark O'Neal]

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.

[Krooser]

Thanks guys...

Thought the 4032 was a form of a hyper piston... now I know.

Always used 2618's in my race stuff... this will be a custom piston built to copy the Ross domes that were in the engine. I'll likley use a smaller ring pack than the 1/16-1/16-3/16 that was used before.

Good idea about matching the piston to the current bore. I'll take the block to my machinist as I only have a Chi-Com dial bore gauge that I don't want to trust... or is it me I don't trust?

As always...thanks for the input.

[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

[Newold1]

Use the 2618 and even with a bore hone to clean up the cylinders the clearances should still be in a good range for 2618 forged pistons. I would recommend you try to keep your piston and rod combined weight at a light number so ask Randy who he can help and supply a 2618 piston that with your rods will keep those weights down, your little dirt track engine will like that better. JMO

[Mark O'Neal]

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.

[digger]

whatever wizardry one does with skirts on 2618 can be done on 4032 so the 4032 will still be able to run slightly tighter. i don't think it matters on most applications that people here would be concerned with