Flat head combustion chamber

You;re welcome. Adding to the collective knowledge pile I hope.

It is easy, now, to see how primitive it is. but that's really a measure of just how fast technologies have been changing these last 50, and literally, 5, years. It's nuts now what's possible.

With the Lhead, or OHV, block clean and on a bench it is not hard to visualize the wooden model the mold was made from. I sliced up an dead OHV head to see the water jacketing. Its awful! "Flow" is a generous word! Better was possible then for sure, but cost mattered. Computational machines were Comptometers and Brunsviga's, and paper pads and slide rules. This iron tech was based on older crafts-based approaches to problem-solving.  Its an explosion in a hole, push a lever, wear out in 10 years, buy another. 

From what I can tell from reading, these old Nash inline sixes were considered pretty good tech for their time. I think though that applied to the seven-mains motors, not necessarily these little low-end things. The forged crank is high quality, but my good machinist says it is very ropey. I had rear seal issues, he pulled the rear main cap off (car on a lift), loosened the 3rd, the crank sagged enough to rotate a new seal in. With better metals, and stress and dynamical analysis, you can make twice as siff today with a fraction of the material. 

Also the bearings are too large and too wide. It heats the oil, lol! My ohv, 30 minutes held at 2800-3000 rpm high load the oil temp rises to 220F, and Ive got a huge 8" x 8" multi-pass cooler with fan and full-flow oil pump. 30 minutes at 3500 rpm and load and the oil runs 240F, with the cooler fan on.

THe big bearings probably seemed like a great idea back then. Bigger than small is good, but bigger than adequate is worse. Etc. 

I agree on the sharp edges. The weird bulge on the inside of the valve pocket too is sharp edged. Id ground mine as much as I dared -- there's water jacket in there -- and rounded the sharp edges. 

One upside to primitive iron is it's susceptible to new techniques and plain old care.

How high do you dare rev it, for passing, etc?

How high rpm would you dare to cruise at?

It had a Fenton head with 2 1 bbls., and overdrive.

I never had a tach , I'd rev it till it till it just wouldn't rev no more sometimes.

In road test of new flatheads,  they reved to 5000.

I'm sure I was at least that high.

This was my first real overhaul of a engine.

About as soon as I got it running good I got sudden orders to Asia.

With only 10 days  warning before I had to be at Travis AFB to ship out,  I had to sell it to a friend in the USAF.

When I look at the somewhat kidney shaped chamber I'm also left to ponder if any of the modern swirl technology was deliberate???

It's a gas, so pressure would be essentially equal on all surfaces, standard gas behavior with the "acoustic" behavior of moving gases.

THe volume is a weird shape, flame propagation is probably terrible, dead, cold, hot spots, etc.

Combustion tech is crazy now. I read about a HOnda engine (I don't think its all that unique) that direct-injects into a cup on the top of the piston with precisely controlled swirl, that will routinely burn 60:1 A/F. WOT accelleration is stoichiometric!