Can someone explain why crossflow heads vs counterflow heads seem to be the preference? Are crossflow heads more efficient and if so why? I am talking pushrod engines here.
Consider that the head designer has to fit both the intake and exhaust ports in the same real estate as the head bolts want to occupy, and you'll realise that the ability to use both sides of the head to snake the ports through those bosses will allow better port flow with a crossflow head. The only reason to put both ports on the same side of the head is packaging and installed cost, although I guess it is easier to get manifold heat to the carb on gasoline engines with the non-crossflow design, and the head casting may be smaller so it would weigh less.
All you need to do is look at the port arrangement of an old Wayne head for the GMC six and the stock head and the difference is easy to see. Cosworth turned the little Ford V-8 into a world dominating F1 engine with their version of cross flow.
A crossflow head can flow more than a U-flow because it is a relatively straight shot across the chamber for the incoming charge and there is better scavenging so you'll get a denser, purer charge and more power from a crossflow, all things being equal. Two of my altered roadsters use Ford 300 sixes. The orange one has a standard U-flow head; the blue car has a crossflow head. The blue car is 7-tenths quicker in the quarter.
I would think that putting the intake ports on one side of the head and the exhaust ports on the opposite side gives the head designer way more leeway on port placement. So rather than be restricted to a small amount of real estate trying to cram the porting into just one side of the head, you have more room to design more efficient and better flowing head ports. Another big plus for the inliners is not having one side of the engine crowded with both the intake and exhaust manifolds.
Apart from the problem with available space inside the head on a counterflow head, you also have the inlet and exhaust manifold sharing the same space outside the engine. Harder to give the manifolds the best design when they have to share space with each other. A set of Weber carbs on one side and headers on the other is much simpler, and looks better.
I sold my Bonneville Altered coupe down under. The buyer told me he as going to run a twin turbo 300 Ford six with the Australian cross flow head. So I took his word for it. Otherwise it's finding it out in the shop.
The 300 crossflow head was an experimental prototype. Ford never put it into production, instead electing to go with a V6. The Aussie Ford crossflow heads will not fir a 300 six. They will fit a 250 with some block modifications.
could a U-shaped head flow as much as a crossflow head, all things being equal? Particularly with high ports or will the scavaging effect of a crossflow head always win out over a U-shaped head? just curious.
I remember an article in one of the car mags back in the early 70s, that described a head for a Ford 300 that was a couple of 351 Cleveland heads sliced and diced and furnace brazed together. IIRC the engine was in a Maverick D/MP drag car.
I don't think there is any effect from the valves being at right angles to the crank, (the valves are the same distance apart, just different relationship to the crank) It is all about better ports on the cross flow, because the designer doesn't have to jamb them all on one side of the head and still make room for head and manifold bolts
If I remember right Ford SOV catalog offered a racing cross flow aluminum head for a 300 it did not have water jackets.
Speaking of valve angles..Yates took angle out of the SVO clevland heads and made more power; so nascar made them the head to use..If I remember right the nascar [or other for that matter] chevy heads they made have less angle also for better flow, 18° sticks in my head..In an engine with a SOHC and bucket followers then doing ports on one side of head is real douable since you don't have to deal with push rod/rockers but opposite sides would still probably be the most beneficial..
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