David T.

While researching superchargers etc. I came across of the engine design called Miller Cycle engine. Basic idea is to leave intake valve open for about 10%-20% of the compression stroke thus effectively reducing compression ratio while keeping the higher expansion ratio, which reduces the risk of detonation for supercharged engine while more effectively using all the power from expansion stroke:

The Inside Story on the Miller-cycle engine

Now, this seems much easier way of reducing compression ratio then new pistons and cylinders. If only I can get Jerry Woods or some one to design such cams :-)

aquabat911

I agree with you David, Mazda used a Miller cycle moter on the 929(I think) for several years and a few of the automotive publication did small side bars on it but that was about it. I think if they would have used it on a sports-car maybe it would have got more attention. I think we are far from maximizing the potential of engines and I don't understand why most car companies are reluctant to develop new technologies. Slide valves, rotating valves, there's so many different things that could be developed but for some reason aren't. I guess it all comes down to what people are willing to pay for.

Chris Bennet

There are probably good reasons besides cost that we don't see some things like miller cycle engines. I'm just guessing but perhaps it has something to do with emmisions.
-Chris

pig4bill

I know what you mean about valve technology. I used to work at a company that made linear motion controls. i.e. a small box that can make something move from side to side, controlled by electronics. I felt it would only be a matter of time before it was adapted to F1 cars. Can you imagine - valve opening and closing completely controlled by electronics, tune for low-end, middle-range, and high-end all at the same time. Tune for gas mileage at the flick of a switch. Want to try a new profile? No need to wait for cams to be ground and tear the engine apart, simply re-program the controls. 5 valve heads with a different profile for each valve. Oh well....

forry@gmc

Depending on the camshaft design you use, you maybe reducing your compression already.

If you are using a camshaft with a a lot of overlap (the time when both the intake and exhaust valves are open) you are lowering the static compression ratio. Why? Because the exhaust valve is still open as the piston has started up on the compression stroke, therefore reducing that volumn to compress. This is good in scavenging the cylinder to make sure you have a clean charge for the next burn, but lowers the dynamic compression.

Forry Hargitt
German Motor Cars, Inc.
Homepage

RobC

Actually I was under the impression that Renault were using, or evaluating, this technology for their 111 degree v10 used by the Benetton team. Of course this motor really stinks at the moment, for whatever reason.

I wonder what would be more dependable: mechanically accuated values or electronically controlled. When one considers the cost of bent valves and destroyed pistons this becomes an important issue. In F1 they expect to rebuild the motor after each race, but I would want to get at least 100,000 miles out my own.