I just got to taking my 46 59A flatty's heads off to inspect for wear and this is what I found. Releived on the intake side only, intake valves say Ford on them. Very clean inside. Block has traces of maroon metallic paint on it. Bore is stadard, I am going in to look at the valvetrain next. Why would someone relieve the itake only?
I would suspect the thinking was to get the tumble more over the piston. instead of detonating with the mix mostly on the edge as Ive seen in "smarter guys than me" flow charts. Hard to tell on my phone but is the exhaust valve bigger than the intake?
That is a type of relief that was used by Harley Davidson when modifying their flathead V-Twins. I have seen drawings of this type of relief. This idea was picked up by flathead folk, the idea being, as suggested already, to increase intake flow but to retain as much compression as possible.
Here is my current project, done the relief last week... I have done this to match the Edelbrock block letter heads...
I have seen one such intake-only relief, on a circle track engine in Pennsylvania in late 1960's. Compression is probably the actual explanation for "why", but there may be more. Flatdog once told me he had been studying exhaust flow and had observed that the exhaust flowed mostly on the INTAKE side of the chamber, tucking into the exhaust valve kind of sideways! This is why you need a good parapsychologist on call when studying flatheads...
looks to me that both sides have been relieved but the intake side more so. can be seen here http://www.jalopyjournal.com/forum/showthread.php?t=420484&page=2 and here http://www.jalopyjournal.com/forum/showthread.php?t=596271
mike davidson, the aussie flathead guru, claims the intake-side-only relief is the hot setup. but didn't barney navarro's heads put a deeper relief on the exhaust side?
There are two basic schools of thought on 4 stroke engine breathing, one school believes that you need bigger intake valves and better intake porting to get as much mix into the cylinder as possible. Those are the fellas running 800 cfm carbs in a situation where a 600 cfm carb would produce proper results. The other school of thought is that if you have clean cylinders you don't need as much intake volumn. They also believe that it is easier to get mix in then to get mix out. Those are the fellas running the smaller carb and getting the same or better results than the big intake guys. I think that different engines bring their own problems but the answer to some fellas (think old timers) is concentrate on the exhaust side and others will concentrate on the intake side. I have heard from a lot of flathead guys that they are weakest on the exhaust side, thus splitting the center port etc. The engine in the original picture looks to be relieved wither at the factory or by someone who is more meticulas than your average backyard builder.
I have seen a couple of blocks with the single side relieving. I think it's factory, but for what I have no idea.