Why destroke a 400 or is this a race engine with displacements limits? Destroking increases friction losses in an engine by requiring the same engine to run at a higher rotational speed to achieve the same piston speed. That's one reason why you make less power when destroking an engine.

Remember that I'm talking about displacement and not two different 377s. I'm talking a 406 vs a 377. The 406 will always win.

 

Thoughts:

VEs well over 100% are regularly seen with "valved" engines, even 2-valve pushrod engines.

I'm trying to envision you big valve that disappers and reappears quickly(?). I'm not sure how you plan to operate it or where it goes when it's open. The shutter of a camera comes to mind, or the iris of the eye, but then where is the combustion chamber. If it's all in the piston, the movable valve becomes the top of the chamber and heat transfer or just the ability to withstand combustion heat becomes a concern. Materials are always a concern, as well as how to move the valve.

The big bore engine would allow a larger valve, rignt? A longer stroke means you reach the physically limiting piston speed at lower rpm, and if we want mega power from a given displacement we need to cycle it as fast as possible; more total air processed per minute. Piston speed "limits" are more frictional and perhaps sealing issues rather than airflow.

In order to move the air into the cylinder, there has to be a slight negative pressure (relative to ambient pressure) in the cylinder. Good race engines get that to 0.1 psi or less now. To achieve 100%+ VE, intake tuning causes a positive pressure at the valve just about the time it is closing. This exceeds 5 psi in some NA engines. You would still need this to be better than a conventional valved engine, and I'm still thinking about how to do this with a 4 inch dia. inlet port feeding the mega-valve.

As to sharing flow, it's kinda like our body; we take air in and out as well as food in thru the same port (mouth). The little valve which controls what goes where, the epiglotis I think it's called, has one heck of a "cam" running it. You'd need something like that I thnk.

While I enjoy "thought experiments", I tend to fall on the practical side of how can we physically accomplish this?. In my business I get drawings of parts that need to be produced, but which are difficult, or nearly impossible to economically produce. You know the type of part: no weight, impervious to everything and made from unobtanium. Oh yeah, when we finally found some unobtanium it was also known as "unmachinabilium". (no offense to M.Donahue intended).

Even with a valve that would open instantly or disappear, you still have to accelerate the mass of air which doesn't occur instantly, so you'd probably still need some little exhaust/inlet overlap to make exhaust tuning work. Maybe not.

I'm not trying to be a wet blanket, but other than not having a clue how to construct your engine, I'm not sure it would be more powerful. It's amazing what over a century of development has done for the poppet valve 4-stroke engine. How about some help as to how to work this valve system, and we'll go from there.

My $.02

 

I am no physicist, nor do I have a degree in engineering, and I completely understand your concerns for my idea. But, from what i know, which is a decent amount, i feel, about physics, math, engineering, this should be a feasible, well-working concept. I am afraid to share detailed information about it, i dunno, would you be willing to talk some about it off the board?

Anyway, my current thoughts:
Should be able to still have intake, exhaust overlap.
Should be able to withstand large amounts of pressure/power.
Would take some energy to keep working, but not similar in comparison to the hp that a current poppet valvetrain consumes.
Should take considerable less overall friction to "run."
Won't be able to make "valve" opening quite as big as cylinder, unless i can come up with a solution to a current problem i am thinking of, but you are correct, that with larger bore size, the "valve" size could be enlargened, which i am sorta thinking is somewhat of a key.
I am guessing that in the long run, with tons of R&D, which i cant even imagine spending at this point, that there would ultimately be a perfect middle between bore size, with its accompanying valve size, and stroke. I would then assume, based on this, that every bore and stroke combo would be different depending on planned/desired cubes. I dont know if anyone has ever done this with a regular N/A motor, meaning test every bore-stroke combo given a certain displacement, and then compared results. I think that would be very interesting, and might bring some light to the topic.

 

I read a Hot Rod magazine article a few years back that followed an SAE class through a build up of the most efficient big-block they could build. I belive the block of choise was an Olds, but the number that sticks out in my mind was 108% VE... probably the highest VE I've ever seen in print from an NA engine (although I'm sure the ultra-double-secrete NASCAR/NHRA/F1 labs all have examples beyond this ).

For an even easier VE gain, I read once that Boneville racers find a 5psi boost around 200mph with a properly designed intake scoop.

Quote:

Oh yeah, when we finally found some unobtanium it was also known as "unmachinabilium". (no offense to M.Donahue intended).

oh come on now... that's what tactile nukes are for... casting unmachinabilium.

Personally I'll take one crank of unobtanium... and counter-balance the rods.

 

 

One conclusion, sorry, lil off topic, and correct me if i am wrong...No matter the friction, whether it be from the rings or other places, most extreme power motors (N/A) are limited to a bore size. Based off that, you are then limited to a stroke size via limitations from the deck height. So if looking for n/a power, why doesnt everyone just do a max safe bore and a max stroke. Maybe you wont be able to turn as many rpms, but you can work the kinks out through the tranny gearing and the rear end gearing. I think it would all turn out almost the same in the end. IF you have a short stroke motor, turning tons of rpms, somewhat reducing ring friction possibly, you are still gonna lose more power in your drivetrain, seeing how u are gonna have more rpms in ur drivetrain. If you have a lond stroke motor turning considerable less rpms, maybe making more friction, you are gonna have less drivetrain inertia given its lower rpms. Correct me if i am wrong, but all in all, it looks pretty much equal. To me it is a question of whether you're gonna wanna hear that motor screaming at 10k rpms all the time when you floor it, everything vibrating its a$$ off, or whether you are gonna want a low end torque monster you have to shift at 5000 or 5500 rpms...

Bout my whole cylinder head/valvetrain thing, anyone know of a good machine shop within a couple hundred miles of the DC area that will be willing to work with me when i get some funds saved up and want to start making these custom heads???

 

"No replacement for displacement" (assuming NA) strikes again.

That's pretty much accurate if you can get the intake to flow well enough on the 450+ cube small block.

As to drivetrain losses, the only thing that turns engine rpm is flywheel, clutch and trans input shaft. The rpms (and losses) get progressively lower as you get to the axles where they are about the same...big slow engine or small fast engine.

Look at where an engine needs to operate and then see how to ge the most area under the torque curve and the hp curve in that rpm band. A 5000+ stall drag car will obviously have different requirements from a 4200 lb. under 2500 rpm stall street car.

It isn't just friction losses that effect long strokes, high rpms and large displacements. Don't get lost in friction. Yeah, all else being equal (or regulated by class rules) a couple of friction hp can be critical (Cup plate engines, for example), but generally spend you $ on better airflow.
My $.02