Ported 026 Squish Check

[Mastermind]

Does this thread have anything in common like i was asking you about last week in the pm ?

I can't remember what I ate for breakfast.......so I doubt it.

 

[Mastermind]

And what Al is saying about quench area is spot on from everything I've read on the subject. Considering that I read everything I get my hands on about new engine design, the subject is well followed for me.

 

[Moparmyway]

Without building a head, we are sorta stuck with the factory chamber. In many cases I want to get the exhaust port down, and that alone determines the amount I remove from the squish band.

Who here has put their eye on the new 661 combustion chamber, and measured the width and taper of the squish band?

I think if you take a hard look at what Stihl did there, you might be very surprised....

Exactely, and if that makes the squish band too wide, I can see getting the chamber larger and the band smaller as a way to increase efficiency

 

[drf255]

The new hemi.

 

[drf255]

The old 426 Hemi Chamber

 

[redfin]

Is there an optimal band width percentage vrs bore diameter?

 

[Chris-PA]

The new hemi.

If ya need two plugs to light it...........

 

[Mastermind]

Exactely, and if that makes the squish band too wide, I can see getting the chamber larger and the band smaller as a way to increase efficiency

What is too wide though?

 

[drf255]

A wider and more evenly distributed downforce on a piston should give better power and less piston stress. But there"s always a tradeoff of less swirls and incomplete chaotic ignition with less squish.

There is likely some optimal balance.

A standard 026 chamber is hemispherical up to the central combustion chamber. The factory squish area is small, like 4mm, but the remainder of the chamber up to the combustion area is like one very large but looser squish area.

Even though my flat squish area is tighter in clearance, it's actually alot smaller than the effective factory hemispherical area.

 

[Deets066]

 

[Mastermind]

You ok Deets?

 

[drf255]

The standard chamber Deetsy.

See what I mean?

The surface area of the entire squish (not just the tight peripheral area) is greater than the flat cut one. Just not as tight.

 

[blsnelling]

What do they look like after you cut them? I certainly wouldn't think you'd want to cut that small squishband out. You'd be back like that 1950s Homelite technology, lol.

 

[drf255]

What do they look like after you cut them? I certainly wouldn't think you'd want to cut that small squishband out. You'd be back like that 1950s Homelite technology, lol.

We're talking .020 difference between the factory band and the arced area up to the combustion chamber. So youre losing a bunch of volume in the area.

 

[Deets066]

You ok Deets?

Yeah I'm good now, wings and 3 tall blue moons for a late lunch.

 

[Deets066]

We're talking .020 difference between the factory band and the arced area up to the combustion chamber. So youre losing a bunch of volume in the area.

Do you leave any dome on the piston when you cut the chamber this way? Or just cut the piston flat? I'm thinkin flat would be best

 

[blsnelling]

We're talking .020 difference between the factory band and the arced area up to the combustion chamber. So youre losing a bunch of volume in the area.

Looks like a very poor head design.

 

[Moparmyway]

What is too wide though?

Sounds like a good time to experiment with my lathe

 

[drf255]

Do you leave any dome on the piston when you cut the chamber this way? Or just cut the piston flat? I'm thinkin flat would be best

I've actually been leaving .020 of the dome edge and cutting the remainder flat.

Leaves a drop of a dead area, but gives me a drop more compression height. I dont have to cut the base as much, and i can take more from the chamber to get the exhaust lower, while still not freeporting.

I can also sand the final squish that way and leave the chamber edge a bit round by .006. It fills the void that the piston edge chamfer creates.

 

[Mastermind]

Looks like a very poor head design.

I agree. The 026 is an antique.