Diagonally opposed valves

[Martin F]

Been reading about some of the engines that had inlet and exhaust valves right next to each other in a four valve combustion chamber. This has prompted me to wonder how the camshaft would activate the valves when they aren't all in a line.

To explain a bit further in a normal twin cam engine with four valves per cylinder you have all the exhaust valves on one side of the combustion chamber and all the inlet on the other. In the type that i was reading about, they have on one side exhaust, inlet, exhaust, inltet........ and the on the other inlet, exhuast, inlet, exhaust............. So this lead me to wonder how they actually activate the valves when one cam is for inlet and the other is exhaust ? Usually its not a problem as all the intake and exhaust valves are in a line. Only way i can think of doing it is by using the cam with followers method which can be problematic in high lift applications IIRC.

Anybody come across one of these engines ?

[Chris Wilson]

The lobes on he cams are just machined with correct lift and timing for each valve, so lobes paired together have different profiles, IYSWIM?

It has the downside of limiting the timing variations adjustable pulleys can offer, so the engines have to pretty much live with what is machined into the cams.

[Martin F]

Quote[/b] (Chris Wilson @ May 30 2004,21:32)]The lobes on he cams are just machined with correct lift and timing for each valve, so lobes paired together have different profiles, IYSWIM?
Doh !! Such an obvious solution.

[Nathan]

Why would anyone want a rather warm exhaust valve and port any closer to an inlet than they are even with the conventional opposed setups?! Massey Ferguson probably wouldn't care, but on a road car?

[Darren Blake]

It produces huge amounts of swirl in the combustion chamber.

I think it's an advantage in direct injection diesel engines. IIRC the GM DI diesel engine had this setup with almost vertical valves.

[Nathan]

Ah. That makes sense. Especially with a diesel. Mr Ferguson probably would be interested then http://www.mkivsupra.co.uk/iB_html/non-cgi/emoticons/smile.gif

[Martin F]

Quote[/b] (Nathan @ June 01 2004,10:55)]Why would anyone want a rather warm exhaust valve and port any closer to an inlet than they are even with the conventional opposed setups?! Massey Ferguson probably wouldn't care, but on a road car?
Yep, but looking at that on the flip side, you have a nice cold inlet port next to your exhaust port.