AHC: More Widespread Use of Pushrod Engines and Superchargers for Automobiles

Delta Force

Banned
I think once you go to multi-valve the pushrod becomes less economical in terms of construction. The beauty of your average pushrod engine is a minimum of expensive, machined parts. The cam is about all that needs machining, lifters and pushrods are mass produced and rockers are even stamped out of steel sheet. That all works because the geometry is simple and standard.

Once you start getting fancy geometry for rockers and multiple valves then it becomes easier just to machine another cam and minimise the rest of the valetrain by putting the cam up on top of the head.

As for blowers, the biggest problem for roots type blowers is heating of the intake charge. If intercoolers became more common then roots type blowers could be seen on a lot more production cars.

Most multi-valve engines tend to be dual camshaft, at least for engines with four or more valves. Have there been any dual camshaft pushrod engines? Could the cams/valves be doubled and separated into intake and exhaust systems without having to change everything else?
 
I think there have been engines with cams down low either side of the block driving the valves on their respective sides on the head. But its not common and I'm not surprised, if you are going to have 2 cams per head and hemispherical combustion chambers why not just make things easy and put the cams up on top.
 
What's the valve geometry like on those diesel engines? Diesels have numerous different design requirements than petrol engines so the assumptions for one don't necessarily hold true for the other.
 
IMO a lot of the DOHC 4 valve cumbustion chamber use right now is driven by marketing, at least in NA. Europe has long tended to have tax and liscencing regulations favoring low displacement high output engines. But in the long run does one really need it all? My previous vehicle was a Dodge Caravan. The long wheelbase version. It had a 3.3 liter pushrod v6 and frankly it had more than enough power for every thing it was ever asked to do.
One thing that could of been tried with pushrod vee types is to have two camshafts in the valley. Both Ford and GM tried stacked camshafts. One for intake and one for exhaust. The idea I've thought about and plan on using in a TM coming soon is one cam high up on the cylinder bank. This results in a very short and stiff pushrod. In the 80s I had a couple of Renualt 18s that had pushrod hemi heads. The cam was so high up on the block the timing sprocket and chain were partiallly inaside the head. By reducing valve train mass and reducing the work load on the cam a multi valve pushrod might be more practical
 
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