2618 Piston Street Use Longevity

[Warp Speed]

The clearance spec is .0002-.0011.

So what does that tell us, and why does it make that a superior design?!?

[modok]

That piston probably IS very good at what it does, but I's made to fit the special issue open deck siamese aluminum block with oxide composite nougat center.
Put it in a rigid iron cylinder and lets see what happens.

[digger]

Sorry i'm from the future so 100% metric, have to dumb down and then the wheels fall off as imperial means nothing to me.
.1mm = .004 right? I got told off on here for being over precise, but I think that is .00393701

What alloy are they ? 0.04mm is 0.0016". A piston that size would be 0.0020-0.0025" in 4032 according to JE. Pretty much all forged Pistons I've used are oval shaped in plan view and barrel shaped in elevation view.

Can you tell us how the ovality and barrel sizes compares between the oe and aftermarket forged?

I don't think we're on the same page here.
.1mm = .004" which is the typical piston/bore clearance you are advised to use by aftermarket forged piston manufacturers at an approx bore size of 86 - 87 mm.
Now go back and read the Honda manual and see what their recommended clearance is on a well designed forged piston, there you will find the answer to your question.
The only reason I plucked that particular engine out of the ether is because it is a reliable production car engine making high power and has forged pistons fitted as standard. Whilst it is a World leader, other engines are available which also use forged pistons, try to get one and examine it.
I have no idea why this is turning into a pissing contest about who makes the best engines, you've missed the point if you want to go there, maybe my posts are being derailed for a reason....
I have no idea what grade of alloy it is, I also don't think it is really relevant to the point I am making, but agreeably it would be interesting to find out.

The ovality I mention is around the top ringland i.e. if you were looking down onto the top of the piston crown, Elliptical is maybe a better term. Yes I know skirts are elliptical.
The barrel shape is also just the top ringland viewed from the side, not the whole piston shape which I know is also that shape.
I'm trying to lead you to the water, I can't force you to drink it. I was hoping for a debate on how we can look at a well designed piston, take some notes, discuss why they did such a thing and how it could possibly be incorporated in your own pistons.
I hope you are understanding now.

JE state 0.0020-0.0025" for the same size and type of application as the OE you mentioned with 4032 alloy, the other alloy they use 2618 it is 0.0030-0.0035".

their piston is elliptical/oval to at the top ring to....

[4vpc]

JE state 0.0020-0.0025" for the same size and type of application as the OE you mentioned with 4032 alloy, the other alloy they use 2618 it is 0.0030-0.0035".

their piston is elliptical/oval at the top ring too....

Ok, what is your source for that information?

[4vpc]

That piston probably IS very good at what it does, but I's made to fit the special issue open deck siamese aluminum block with oxide composite nougat center.
Put it in a rigid iron cylinder and lets see what happens.

Yes it's a good point, i'm not saying you go all the way and copy their bore clearance exactly, but it does lead you to believe that we can close that gap up considerately given they are at one extreme and the other.

[modok]

I might agree with you or I might not, need to have the piston IN hand to see how it's made and how it measures.
Have you chosen this particular engine because aftermarket pistons are being used because OE are too expensive?
Maybe the aftermarket didn't intend for them to be stock replacements, but they are being used as such. I'd believe that.

[digger]

JE state 0.0020-0.0025" for the same size and type of application as the OE you mentioned with 4032 alloy, the other alloy they use 2618 it is 0.0030-0.0035".

their piston is elliptical/oval at the top ring too....

Ok, what is your source for that information?

https://www.jepistons.com/PDFs/TechCorn ... rc4032.pdf

https://www.jepistons.com/PDFs/TechCorn ... rc2618.pdf

Clearance data above

[4vpc]

I might agree with you or I might not, need to have the piston IN hand to see how it's made and how it measures.
Have you chosen this particular engine because aftermarket pistons are being used because OE are too expensive?
Maybe the aftermarket didn't intend for them to be stock replacements, but they are being used as such. I'd believe that.

Yup, that's why i'm suggesting taking a look at one.
As previously mentioned, I only chose that engine as someone has already done the R&D for me, there are probably other production engines which are successful in many ways and use forged pistons, that's just the first one I discovered and had access to a piston. Find out who else uses them in production engines and grab a used one, someone mentioned one earlier in the thread.

[4vpc]

JE state 0.0020-0.0025" for the same size and type of application as the OE you mentioned with 4032 alloy, the other alloy they use 2618 it is 0.0030-0.0035".

their piston is elliptical/oval at the top ring too....

Ok, what is your source for that information?

https://www.jepistons.com/PDFs/TechCorn ... rc4032.pdf

https://www.jepistons.com/PDFs/TechCorn ... rc2618.pdf

Clearance data above

That is just a generic guide, it says nothing about Honda or the piston being elliptical at the top. It doesn't take into consideration block material either.
Also note the clearance difference, it's .0020, whereas Hondas is .0002 wonder why
JE have also said that it doesn't matter whether your piston is 2.5 or 3.625" you just use the same clearance. So a 2.5 piston expands as much as a 3.625 one?

For some reason you're acting like I've knocked on your door and am trying to sell you something you don't need, it's a strange way to act when that isn't what i'm doing.
I'm just putting something up for debate and saying give it some consideration rather than dismissing it.

[RCJ]

Good info. So what is the more durable design on street the narrow x forging or a wide round skirt?

"I" would stay away from an X forging for the street. I don't see any benefit. Race engine yes on the x forging. I am only one person and one opinion. Others may have a different opinion and that is fine.

Can expand on when an X forging is best vs. a full round.What would you use when you know you have excessive clearance, alloy or design.What would you use in an oval track motor when there is a good chance of high water and oil temps.

[digger]

Ok, what is your source for that information?

https://www.jepistons.com/PDFs/TechCorn ... rc4032.pdf

https://www.jepistons.com/PDFs/TechCorn ... rc2618.pdf

Clearance data above

That is just a generic guide, it says nothing about Honda or the piston being elliptical at the top. It doesn't take into consideration block material either.
Also note the clearance difference, it's .0020, whereas Hondas is .0002 wonder why
JE have also said that it doesn't matter whether your piston is 2.5 or 3.625" you just use the same clearance. So a 2.5 piston expands as much as a 3.625 one?

For some reason you're acting like I've knocked on your door and am trying to sell you something you don't need, it's a strange way to act when that isn't what i'm doing.
I'm just putting something up for debate and saying give it some consideration rather than dismissing it.

ofcourse it is generic if you contact them i'm sure they can be more specific, i was just pointing out what the ballpark clearances one aftermarket supplier would recommend, JE is just one supplier that had data easy to find in google.
it seems to be pretty clear that 2.5-3.625" the range is 0.0020-0.0025" so if you have a 2.5" piston then maybe 0.0020" would be a target but if you have 3.625" then maybe 0.0025" would be better, of if in between maybe just interpolate. as for ellipical shape the pistons ive measured are elliptical when ive used them before JE, Mahle MS, Wiseco etc. it would be interesting to compare the amount of ovality

there is a really good paper about pistons, it talks about ovality, barrel shape and temperature profiles

https://cdm.ing.unimo.it/files/progetto ... mbH%29.pdf

[modok]

I don't see anything unusual about any of it.
If double checking the clearance first thing I will do is check clearance at the other end of the skirt.
The clearance at the top of the skirt is MORe important.
The bottom clearance may be more or less just depending on the severity of the taper and also the length of the skirt, and also how flexible the piston is.
The clearance at the top of the skirt is a more meaningful measurement IMO, but the bottom has become the standard point to measure probably because... it is easier?

An iron piston in an iron cylinder. An aluminum piston in an aluminum cylinder. Which one needs more clearance?

[MadBill]

Given the same piston and bore temperatures for both, the latter will see more differential expansion and thus could be expected to need more cold clearance.

[modok]

??? I don't know actually, but thinking about it you have to consider a lot of factors.
I would propose that if we assume the pistons are very conservative designs with full skirts, BOTTOM of the skirt is near the same temp as the cylinder in both cases then they both can run very tight.
But the clearance at the TOp of the skirt, has to have something to do with hot much hotter the piston will get than the cylinder, which is very much application specific.

Open deck aluminum block engines can run zero clearance, and siamese open deck blocks benefit from oval top pistons.
Cool stuff indeed! Different pistons for different holes.

[4vpc]

ofcourse it is generic if you contact them i'm sure they can be more specific, i was just pointing out what the ballpark clearances one aftermarket supplier would recommend, JE is just one supplier that had data easy to find in google.
it seems to be pretty clear that 2.5-3.625" the range is 0.0020-0.0025" so if you have a 2.5" piston then maybe 0.0020" would be a target but if you have 3.625" then maybe 0.0025" would be better, of if in between maybe just interpolate. as for ellipical shape the pistons ive measured are elliptical when ive used them before JE, Mahle MS, Wiseco etc. it would be interesting to compare the amount of ovality

there is a really good paper about pistons, it talks about ovality, barrel shape and temperature profiles

https://cdm.ing.unimo.it/files/progetto ... mbH%29.pdf

Thanks for that link it will be very useful to my studies, when I get time i'll take a good read of it.
I agree with your range too, but they just send that guide out on a printed sheet supplied with your pistons. They tell us that in a turbo application the pistons run hotter and therefore need more clearance, I wonder if they really do, I suspect so, but...
I asked JE about making an elliptical crown, they told me no. I didn't push it so don't know whether it was 'No, we can't be bothered for low volume' or 'No, we don't have the machinery', but at least they recognised it where some others didn't - that surprised me. Maybe I should revisit the idea with them now you say they do it.
I've reduced my clearances, i've gone from the requested .1mm down to .08 and have suffered no ill effects yet. As the pistons were a bit numb (and round at the top) I haven't dared going any further, I was hoping to incorporate some of these features in order to take it down a bit further in the future.