Squish Ratios and Angles, Combustion Chamber Volume and Shape

[Deets066]

I just made a large rounded cutter to cut the majority of a toroidal chamber at once.

That’s a big piece of hss, good idea though.

 

[srcarr52]

That’s a big piece of hss, good idea though.

I used a chunk of 1/2 keyway stock... it's good enough to cut aluminum.

 

[Wisconsin Welder]

Anyone else having a hard time finding this thread? I go to “Technical Area” under “Chainsaws” and can’t find it. I can only get to it through notifications, but there is also a highlight as least thread posted in tech area. Is it a hidden thread or something?

@Mastermind

Ok, I wasn't the only one. I assumed it was because I'm *s-wordty with computers.

I should be able to get time on the lathe to cut the head off this thing this weekend, fingers crossed, then I'll go from there lol

 

[Deets066]

I used a chunk of 1/2 keyway stock... it's good enough to cut aluminum.

1/2 was enough to get toroidal?

 

[srcarr52]

1/2 was enough to get toroidal?

Get close, than you can tram around to get the rest.

 

[huskyhank]

What is the purpose of a squish band versus no band? To take up space?

 

[Ketchup]

Look at this Echo piston.



Looks like a small version of what you’re talking about.

So a domed, popup or diagonal squish piston would add piston crown surface area, but is added surface area a good thing? Domed pistons rarely have as much power as flat. Isn’t a dome max surface area?

 

[mdavlee]

Hard shape to get consistent on the manual lathe. Have halfassed done it though.

It really is on the few I did. A moto gp was much easier.

 

[Nutball]

I've always wondered about a really wide squish band and small diameter chamber with the thought that you want a lot of compression, but you want to wait to make it until the very top of the stroke, so you don't loose as much energy since the leverage for compressing at highest at the top of the stroke. I guess then you have to balance how deep the chamber is to get good flow up into it. Maybe that's where the 50% rule came in? Also have a large radius transitioning the band to the chamber?

Also more surface area can transfer more heat, and you want the heat to stay in the cylinder, not going into the piston and head.

 

[rogue60]

My limited knowledge on the matter I just find this kind of stuff interesting. Anyway I always thought a slight tapered in squish band with a flat piston or domed in 2Ts was better for performance gains? the goal being to get everything out of the squish band and into the combustion chamber as fast as possible? guiding it as such giving it an easy pathway and not just using brute force squishing it flat to get it out of the squish band.
Some of the 2T performance shops do all kinds of strange mods to the squish bands and combustion chambers.
Even the basic slits apparently work good on 2T and 4T's to get the fuel/air mix out of the squish band as fast and easy as possible?
Anyways here's some pics of mods they do with performance gains in mind like I said I'm no expert I just find it all very interesting.

 

[rogue60]

 

[Bigmac]

How about a dish piston and inverted band?

 

[Bigmac]

View attachment 271532 View attachment 271533 View attachment 271534 View attachment 271536

Have seen a tested a few of those, trinity racing used to call it there turbo mod, the design with small and angled cuts. We didn’t see any gains or tuning ease. But it didn’t hurt power really either. If the squish isn’t tight enough the groves will fill with carbon

 

[Bigmac]

Look at this Echo piston.

View attachment 271416

Looks like a small version of what you’re talking about.

So a domed, popup or diagonal squish piston would add piston crown surface area, but is added surface area a good thing? Domed pistons rarely have as much power as flat. Isn’t a dome max surface area?

The theory from my understanding is that at domed, Consistent from edge to edge aids in heat transfer from combustion giving more surface area for the heat to be absorbed. Plenty of power can be made with a dome pistons. A pop up can still make power but the flame font isn’t as efficient and can hurt Scavenging in some cases.

 

[mgr1]

Oem piston from a Solo Super Rex

 

[drf256]

The piston acts as the valves in these engines, adding to the complexity.

The crown architecture aids in directing the incoming charge and outgoing exhaust.

It’s fascinating stuff. The piston wash is tough to decipher. Below is the piston wash on one of the best runners I have ever built. Makes no sense, as it looks SO wrong.

 

[drf256]

I just made a large rounded cutter to cut the majority of a toroidal chamber at once.

They actually sell premade carbide round end cutters. Bought a few on eBay for cheap, just never got around to making another head.

 

[Red97]

1/2 was enough to get toroidal?

Weld a busted endmill to a shank and grind whatever shape you like...

 

[rogue60]

How about a dish piston and inverted band? View attachment 271539View attachment 271540

That's some savage squish! Is over my head lol

 

[Ketchup]

For clarity, the 50% we’re talking about is band radius/ combustion chamber radius? The band should not exceed 50%?

Seems like Squish band volume/combustion chamber volume would follow a similar rule but not as balanced. 30sqb/70cbc maybe?