An odd size question

[Turbinepowered]

Completely the opposite of what most folks here seem to seek, what's the smallest waterboxer one could assemble?

Anything under two liters? Anything in a square, near square, or ideally undersquare stroke ratio?

[Badbugtwo]

Completely the opposite of what most folks here seem to seek, what's the smallest waterboxer one could assemble?

Without even asking why…. theoretically speaking, you could go as small as you want. You could either have a stock crank de-stroked or a custom smaller crank made. You could either sleeve the stock cylinders or have custom undersized ones made and custom pistons.

[sideshow]

A small bore would be one off build.
About all that could be be done without custom barrels is de-stroke the crankshaft and a long rod. And the rod would have to bushed for the larger pin.

[tencentlife]

The 1.9 is already under 2liter, but it's way oversquare: 94x69.

To get undersquare, the cylinder walls would have to be mighty thick; they would be strong and stable, but heat flow might be too slow. By the time you get down to undersquare on, say, a 2.1 76mm crank, you might be able to use some already-available flat-topped pistons without CR getting way too high. Gotta do the math on that one.

Of course, inquiring minds want to know: why?

[fastback]

you can also offset grind the crank to 60-62mm stroke .

[sideshow]

I don't like the idea of a flat top, the wasser head has no chamber and the pistons are just so cool. If you did manage to make a super thick barrel, no reason you couldn't trim it down in the name of heat transfer.

[tencentlife]

Yeah but the dished pistons are what makes modding the top ends such a logistical struggle; there's just so few dished-top pistons out there. It almost makes it worth hogging out the heads just to open up more piston possibilities.

Without knowing the OP's goals, it's just wanking off to say anything more, but I'm guessing by his handle this is a turbo app? Ultra-high rpm, perhaps?

[Unkl Ian]

Going significantly smaller on the bore,limits valve sizes.

---

The only reason I can think of, for going smaller,
is to meet a displacement limit for some racing class.

[Piledriver]

What is the goal?

Assuming it's fuel economy, a 1.9 (or destroked version) would probably be an excellent place to start... As well as running a bit of case vacuum and low tension rings.
(Not TOO much case vac on the street, those seals need oil to live, manifold vacuum is a good source, just make sure it's restricted... and ideally purged, a CIS-equipped WCVW is a good design reference, at least as a starting point)

Most friction in an engine is in the ring pack... Some racing setups have only 2 rings... The second ring is an oil scraper on ~any engine regardless, and some designs work far better than others. Dry sump and case vac likely required.

A crank scraper is sorta hard to pull off in an ACVW, but can be worth a few % in efficiency based on other engines.

Having said that, the ACVW has a pretty decent design as far as keeping the crank away from the oil sump regardless, given that the cam/lifters are in the way.

A seriously OVERsquare engine has a lower mean piston velocity for a given displacement, and friction goes up the square of velocity... Which ALSO indicates you probably want to keep the RPM down.

Research cooled EGR a bit as well.

One ADVANTAGE of the "chamber-in-piston" design is you can make the chamber pretty much ANY shape you desire, so if you wanted to (for example) have 90+% of the chamber volume on the exhaust side, and just valve clearance on the intake, you could do so easily.

We're talking full custom pistons for ANY of the combos discussed so far, do a custom "dish" is entirely doable for relatively little more cost.

Based on Marcos head work, one can sink the valves/seats 5mm and use T1 valves, providig the ability to have ~25-30CC "chambers", so the required dish falls into the more usual 10-25CC ones available for a 305 Chevy (for example...)

[Turbinepowered]

At the moment, the goal is to build a good platform for an efficient Dasher-dragger. I was considering a TIV to power the Dasher, but then realized that I'd have anemic heat, so we'll move to the much-maligned waterboxer.

I live in an area with great availability for E85, so I wanted to factor that into the build. High compression to take advantage of the fuel's 105 octane rating.

Looking for a long stroke to make it easier to use a turbocharged Miller cycle to further decrease the displacement and improve efficiency while cruising, yet have power on tap when I need it.

I understand that the friction goes up immensely as velocity goes up, and that long stroke engines have much higher piston velocities than short strokes of the same displacement, but as I understand it the massive bore engines have problems with flame quality and propagation speeds, which would not be good running E85.

[Piledriver]

True, but 94mm-96mm is not a massive bore, and the chamber was designed perfectly for it. Also easy to shape ~any way you wish with custom pistons...

Still no reason not to go Miller cycle with the shorter stroke , it still "works"...

With the right turbo or blower, torque should be no problem.

[Unkl Ian]

E85 will tolerate more compression, than straight gasoline.

With custom pistons,you can bias the dish to the exhaust side,
( ENDYN style) then you don't need as much advance.

Dual plugs would also be helpful, to further reduce the advance needed,
not sure if it is practical with the watercooled WBX heads.

[Turbinepowered]

I was going to ask about the dual plug option, but that's probably something I can forum surf for.

So a 1.9 was the smallest waterboxer built? With what, a 94mm bore and 69mm stroke? Off the top of my head, I guess... I'd much rather have something that would generate torque on its own merits, like a near reverse of that, like the early diesels were (76.5x81mm).


[edited to correct for sleep deprived errors]