We could at this point turn this into a debate about things associated to combustion chamber vs port design but that is not the point of this story. The point being made is this was new territory and to have two design operations, on different continents, working on hugely different engines, to arrive at similar solutions to what was needed, is damned cool.
The easiest way to explain the reasons for the variance in included angle has, In turn, to do with the angle at which the inlet charge enters the cylinder. Design engineers will have their .own views but again a simple explanation is that a narrow valve helps with getting the port angles right for max flow, resulting in higher volumetric efficiency and consequently cylinder filling. The wide valve angles tend to provide better swirl associated with fuel efficiency. Both have good combustion properties and the four valve arrangements give benefits in cylinder filling over a two valve wedge and a two valve Hemi. It is generally accepted today that included angles of around 30° for race engines is a healthy target.
Let’s get to the extent of the work done. It is classic that in the 60’s before we all become clever, both Oldsmobile and Cosworth decided on very flat chambers and narrow included angles. Oldsmobile selected 37°( Inlet 22° Exh 15°) and Cosworth 40° for the FVA.(20° Both) and 32° for the DFV (16° both), all designs being significant departures from that 60° and higher being the more practical norm for 2 valve Hemi applications. This low included angle resulted in an extremely compact, low roof, chamber with the spark plug smack in the centre of activities.. For Olds the decision had, in part, been decided through the use of a unique flow bench used in the port design. Oldsmobile developed their flow bench so as to enable measurement of air flow on a single working cylinder. Interestingly they measured the Exhaust gas volume exiting the exhaust port as the total measure of efficiency. This allowed the team to assess port shapes and valve timing on both pushrod and four cam cylinder heads whilst achieving excellent basics even before the engines fired up for the first time (For 1967 that is SMART). To facilitate testing of different combinations of port shapes and valve geometry, prototypes were made from wood.
The engine block for the two versions of the W engines was common and as already noted, designed for both cast iron as well aluminium manufacture. Cylinder head porting was very similar, with the exception that the pushrod version required channel intrusions into the ports to accommodate the valve actuation. The loss in flow between the two was much less than expected making volumetric efficiency on the pushrod engine a lot closer to the OHC version than expected and hugely better than the original 2V pushrod.
Here again a learning experience for the Cosworth and Oldsmobile boffins. In comparison to equivalent 2v engines, they initially expected 4V flow bench numbers to show improvements in flow throughout the valve lift cycle …not so….The first surprise result was to find that the biggest difference occurred at low and medium valve lifts….with fully open valves almost the same between the new 4V and equivalent 2V. The resultant overall increase in cylinder filling, ultimately being the difference between 4V and 2V engines.
From this we understand why 4V engines have that wonderful torque spread (using suitable long runner inlet tracts)* and achieve impressive power numbers without needing wild valve timing.
* Subsequent developments with Variable Valve Timing have resulted in astonishing cylinder filling capability across the rev range on 4v applications. Even on non turbo engines, many designs flat-lining in healthy areas of the torque curve..
** I was not being offensive when I referred to the Ford Cammer being a cheap and cheerful version of the original, because in the Ford application they had used a reduced cost approach to the development and a single morse chain to drive the two Overhead Cams. The chain was some 7ft long and had massive flex issues…so much so, that cam timing could vary by as much as 6°-8° dynamically between banks. As I understand it though (and it happens this way when any one of us engineers don’t get things quite right)…..the aftermarket has a solution and in this case there was a gear kit available for lovers of the Ford Cammer.
Let’s take look at some of the Olds architecture, the most interesting being the pushrod four valver. The magic is in the layout of the rockers, which because of the narrow valve angle make for a deceptively compact package. The associated pics of the engine complete with rocker covers attest to that. The dual rocker assemblies (individually adjustable) were initially constructed from cast iron, internally bushed and switched to forged aluminium on needle roller bearings. From this point the rest was fairly conventional with the inlet manifold breathing through the venerable Rochester Quadrajet.