Honda/NissanFan

Ok while sitting in my room thinking about how can I get enough $$$ to buy a 350Z or S15, I thought of a good idea on how to make conventional gasoline engines more powerful and efficient. You know how Honda (Vtec & i-Vtec), Toyota (VVTi), and Nissan (CVT & Neo VVL) all use some type of varible valve lift and cam timing. They can varry the setting by varrying the cam sproket (aka cam gears).

Well what if someone came up with the idea of Variable displacement. I think displacement is calculated by factoring int he piston's stroke and bore. Can't image how an engine could varry its bore but what about stroke. There could be some type of gear on the camshaft that could varry the piston's stroke, therefore varrying the displacement. For example stomping on the gas in first gear, at lower rmps (1000-3500) the stroke is longer for more torque, at (3500-5500) the stroke gets smaller for more midrange power, and (5500-7000) the stroke gets even smaller for high end horse power.

What do you think?

MrFatbooty

You aren't going to buy an S15 in this country.

A "gear on the camshaft" is a cam gear.

Changing the stroke requires morphing the shape of the crank and changing the length of the rods. Figuring out how to do that in a motor spinning at thousands of RPM would be next to impossible.

Honda/NissanFan

I know I can't get a S15 in the country. I use to have a S13 (240sx) and I like the S15.

What is the rod that the connecting rods are connected to??? Vary that thing.

Using this in a V6 or V8 would be kinda hard. Maybe a I6 would be better. Maybe some type of hydrallic mechanism could be used, kinda like how the hydrallic system that works on brake caliper pistons.

inspyral

One of the European manufacturers, either SAAB or Volvo if I remember correctly, has a variable compression system that works by tilting the head under certain conditions. This allows the compression ratio to be variable within a certain range. As for variable displacement, that would be much harder to do. If you want to vary the stroke, the only way I can see is to change the length of the rods on the fly. That would be an engineering feat in and of itself. Now, let's say you were able to do that. You would need to take into account the piston to valve clearances, as well as how the compression ratio is going to be affected. Get all that to work together would be an incredibly daunting task. If you leave yourself too little room, your pistons will slap the valves. If you leave too much room, you're base c/r will be very low, which wouldn't be very good for efficiency or performance, really. All of this, on top of the fact that you'd need to engineer a way to alter rod length on the fly. I'm not saying it's impossible, but I doubt we'll see it any time soon, if ever. Oh, and putting some kind of magical stroke-adjusting gear on the camshaft won't work. The camshaft has no effect on the pistons' stroke. Interesting concept, but I don't think it'd be practical.

MrChad

Saab has a proto-type of such an engine.
The displacement varies by change cylinder head volume.
Basically the head pivots in relation to the block. When its up-- its at low Comp. Pivots down and is flat to the block like conventional head (high Comp.)

I've yet to fully understand how the head seals and doesn't leak if I did I'd likely be working at saab

Anyway-GM-is exploring this option which means you have hope they will screw it up.

My current engine dreams are associated with a fuel injected weed wacker.........I hate smelling like 2cycle........

inspyral

You mean the pins? The crankshaft and the rest of the rotating assembly move too quickly over a 360 degree angular displacement. You wouldn't be able to plumb any sort of hydraulics thru the pistons to vary the pins.

inspyral

SAAB's system varies compression, not displacement. Changing the compression ratio does not affect displacement. The bore and stroke remain the same.

Gasoline Fumes

GM sort of had variable displacement in the early eighties. They had a V8 that ran on 4, 6 or 8 cylinders, depending on power requirements. It was called 4-6-8, or something like that. And I've heard it was awful.

Honda/NissanFan

Well i just saw the move "The Transporter" (good movie). I think to make my idea work I would need some type of telescoping connecting rod setup. Now that I think about it, internal combustion engines lose too much energy in heat and their up and down piston motion. Rotary engines are way better, but Mazda hasn't perfected it yet, maybe Honda, BWM, or Nissan should lend a hand.

seth90dx

How about using some kind of spring loaded/clutch or something along those lines to actualy MOVE the whole deal in or out on the CRANKSHAFT? Basicaly the rod connecting to the crank could pull in at higher RPM's and extend at lower RPM's, this would have to work on some kind of enertia based system... Its feasable. I can tell you that (I DONT THINK AT LEAST) Anyone on this forum could build this thing... This would take HUNDREDS of engineers and techies YEARS to figure out.