After Market Popup Piston & Cylinder kits

Nutball · Aug 21, 2019

An advantage the AM companies have when making pop up pistons is that they can start with a taller piston.

Has anyone noticed any AM pistons that are taller than stock? I'm guessing the Cross 390 piston is, but what about the others?

I got to thinking about this when I saw a pop up 56mm 660 BB set. I know the 56mm already free ports bad(at least the brand I got), and having no 56mm gasket, it has no squish without the gasket. So, did they machine more of a free port into it, or just make the piston taller? Hopefully we can make a more educated guess depending on how the other pop up kits are if nobody has tried the 56mm popup.

Czed · Aug 21, 2019

Nutball said:
An advantage the AM companies have when making pop up pistons is that they can start with a taller piston.

Has anyone noticed any AM pistons that are taller than stock? I'm guessing the Cross 390 piston is, but what about the others?

I got to thinking about this when I saw a pop up 56mm 660 BB set. I know the 56mm already free ports bad(at least the brand I got), and having no 56mm gasket, it has no squish without the gasket. So, did they machine more of a free port into it, or just make the piston taller? Hopefully we can make a more educated guess depending on how the other pop up kits are if nobody has tried the 56mm popup.

View attachment 195900

All i can add is the hyway bb popup 372 kit
Is a strong running saw.
I didn't touch anything just bolted it on and tuned it.
Everyone that's run it has been impressed.
But as always consistency
Is unknown with china parts
i have another kit to try.

Nutball · Aug 21, 2019

Thanks for the info, measure the piston next time... What's the squish on that one?

I guess machining marks on the base would help give away whether a taller piston was used or not.

And feel free to discuss any AM popup stuff here.

drf256 · Aug 22, 2019

The dome is usually higher than an oem piston crown as opposed to us making our own on a lathe and dropping the cylinder over it.

One can weld a popup to a crown and turn it down as well, but a manufacturer has the ability to have their slugs cast and machined any way they want them.

BTW, the reason the BB 660 kits free port so badly is that they have shorter skirts than oem. That’s done to insure they fit the case they are put on. The factory 54mm slug’s skirts dip below the case pad at BDC. Usually there is not enough side clearance to allow the 56mm slug to drop down into the case, so the AM responded by removing the skirt. That’s why the Freeport so badly, it’s not the jug design, it’s the intentionally short skirt.

stretch5881 · Aug 22, 2019

The Cross 390 piston is only taller at the popup. I had installed one in a Hyway cylinder and it runs fantastic.

Nutball · Aug 22, 2019

drf256 said:
The dome is usually higher than an oem piston crown as opposed to us making our own on a lathe and dropping the cylinder over it.

One can weld a popup to a crown and turn it down as well, but a manufacturer has the ability to have their slugs cast and machined any way they want them.

BTW, the reason the BB 660 kits free port so badly is that they have shorter skirts than oem. That’s done to insure they fit the case they are put on. The factory 54mm slug’s skirts dip below the case pad at BDC. Usually there is not enough side clearance to allow the 56mm slug to drop down into the case, so the AM responded by removing the skirt. That’s why the Freeport so badly, it’s not the jug design, it’s the intentionally short skirt.

I figured the least they could do is raise the bottom of the exhaust port in their molds.

drf256 · Aug 22, 2019

Nutball said:
I figured the least they could do is raise the bottom of the exhaust port in their molds.

Port would be tiny.

Nutball · Aug 22, 2019

From what I've seen the piston top only goes down as far as it free ports, makes sense. So, that's wasted space, besides they could do this

or

Lightning Performance · Aug 24, 2019

Nutball said:
From what I've seen the piston top only goes down as far as it free ports, makes sense. So, that's wasted space, besides they could do this

View attachment 196079 or View attachment 196080

If only it was that easy. The thermal expansion of the thicker cast just pushed the plating into the rings when the jug wall swells from heat soak in long cuts.

qurotro · Aug 24, 2019

Maybe somebody should tell the AM manufacturer to get ports slightly bigger so all the cylinders come with port jobs.

old guy · Oct 3, 2019

I've been messing with the Hyway popup pistons, I've got 2, 350 huskys up into the 180's comp with base machineing also, my stock 350 is at 115 comp.
A few days ago I put a Hyway popup in my 357 Husky wich already had a base gasket delete, a muff mod and the main jet cross drilled in the zama.
It was blowing 177 on the comp gauge. After some porting & the popup piston install, and after two tanks of fuel she's making 198 lbs. comp.

Ronie · Oct 3, 2019

old guy said:
I've been messing with the Hyway popup pistons, I've got 2, 350 huskys up into the 180's comp with base machineing also, my stock 350 is at 115 comp.
A few days ago I put a Hyway popup in my 357 Husky wich already had a base gasket delete, a muff mod and the main jet cross drilled in the zama.
It was blowing 177 on the comp gauge. After some porting & the popup piston install, and after two tanks of fuel she's making 198 lbs. comp.

I've got a .040 pop up in my 2159 with a Hyway 357 cylinder, it had almost 200 right after install. The Hyway cylinder was very nice but with a gasket delete the squish was .011.

old guy · Oct 3, 2019

.011 is pretty thin, mine, with oem cyl. came to .019-.020.
Are you running that?

Ronie · Oct 4, 2019

old guy said:
.011 is pretty thin, mine, with oem cyl. came to .019-.020.
Are you running that?

The squish is around .020, maybe a little less.

Marshy · Oct 4, 2019

Ronie · Oct 4, 2019

old guy said:
.011 is pretty thin, mine, with oem cyl. came to .019-.020.
Are you running that?

I just found where I wrote the squish down and it's .018.

old guy · Oct 4, 2019

Ronie said:
I just found where I wrote the squish down and it's .018.

That's way more better.

Ronie · Oct 4, 2019

qurotro said:
Maybe somebody should tell the AM manufacturer to get ports slightly bigger so all the cylinders come with port jobs.

The exhaust port on the Hyway 288 is over 3mm bigger than it is on the K&S cylinder I have. The intake is a little over 1mm bigger.

huskyboy · Oct 4, 2019

Ronie said:
The exhaust port on the Hyway 288 is over 3mm bigger than it is on the K&S cylinder I have. The intake is a little over 1mm bigger.

Are the transfer angles more aggressive on the oem jug?

Ronie · Oct 4, 2019

huskyboy said:
Are the transfer angles more aggressive on the oem jug?

I don't remember if one or the other had more of an upward angle but the oem one swept back toward the intake a little more. When I pull the cylinder to change it out with the oem I'll check the upward angles, I think they were pretty flat on both.

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