Recently I came to appreciate an LS1 V8 engine. The nicest way to do this is to stand in the sun near someone who's doing an awful lot of work on one, while carefully depleting their beer supply. Every now and again you can offer valuable advice such as "I'd have taped that hole up BEFORE that spring went in it..." Anyhow, I kept my mouth shut about my confusion regarding the camshafts... until I realized they were buried down inside... "it's OHV!" I thought "like a massive lawnmower engine!" So instead of the conventional arrangement in European and Japanese 4/6 cylinder cars of the valves being actuated by a cam up in the head of the engine, the cam is down near the crank, it moves pushrods which run up the cylinder wall and rockers translate the movement down to the valves. Essentially the cam is remote from the valves it actuates.

How remote could we make this? How about the dash? Wouldn't it be nice to see your hot new cam in action? Mechanical linkages between the cam and the valves might get a touch... complex if the cam were that far away, but we don't need those. So, we turn the cam, lets go with a very carefully controlled brush-less electric motor. The cam acts on followers which move hydraulic pistons. The pistons move hydraulic fluid through nice flexible lines to the complementary pistons which act on the valves. By messing around with the piston sizes you can do exactly what the rockers do, in terms of the ratio of valve lift to cam profile. Now you have a cam spinning in a nice clear case on your dashboard.

A brief read around the fairly involved subject of hydraulics suggest they have no problem with the pressures, the absolute flow rates and so on. The speed of acceleration might be an issue. You could make the whole system one- way flow if you needed, with oil exiting at one end and refilling at the other. You could also control the valve lift by changing the volume of the hydraulic push rod. If you put the cam back in its original location you can use the hydraulics to change lift, and with some clever valving, duration. If you do all that and put the cam on top of the engine, you've got Fiat's multi air system.
-- bs0u0155, Jun 13 2016

Visible V8 https://www.google....FIKHVawBj8Q_AUICCgD
Moves like a real engine, but doesn't burn fuel. [Vernon, Jun 13 2016]

Lots of WW1 aero engines had exposed rockers and valve springs, with pushrod actuation. Building an engine with an OHC engine like that, incorporating hydraulic tappets, would probably be easy enough ... but roller bearings would probably be better than journals, to avoid oil being flung everywhere.
-- 8th of 7, Jun 13 2016


When I first heard about hydraulic tappets/HLA's whatever, I thought they essentially were hydraulic pushrods. Instead they're just there to avoid all that messing about with shims, and, I suspect the collapsed tappets provide easier cranking and the attenuated lift/duration makes for better warm up characteristics.

The Multiair system essentially is a collapsible hydraulic push rod. But they fitted it at the top. The redline is suspiciously low for a DOHC engine. in the mid 6k range, which is well within pushrod V8 territory. I think they could safely ditch the OHC. Since all the timing and lift variation can be controlled by hydraulic valving, you could just go with a gear driven cam down near the crank, or hell, just put lobes on the crank and only use every other rotation.
-- bs0u0155, Jun 13 2016



random, halfbakery