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Ariel Red Hunter · 12-13-2016, 01:46 PM

And it's many brothers and sisters that use the same engine. Luckily for short money guys (like me), foundry technique had progressed to the point to when these engines were first built they already had superb head castings in mass production. Die cast aluminum heads started in the 1930's with radial aircraft engines. You can see, perhaps, the advantage of die cast heads from a production standpoint of engines that required 7 or 9 or 14 or 18 or even more identical heads per engine. By the time WW11 rolled around, die cast heads were in common use. And these were 2nd or 3rd generation heads. Which meant that the intake and exhaust ports were much more sophisticated. The big time manufacturers of the radial engine were Wright, Pratt & Whitney in the US, Bristol in England, and BMW in Germany. Not to forget radials used in Zeros in Japan. So, from this experience came the first die cast heads for motorcycles in the early 1950's in England and Germany. It took 2 or three generations of making die-cast heads in the MC Industry to really get the porting right. Honda did a superb job of designing heads by the sixties and beyond. So the head on the Hawk was perhaps a fifth generation design. And these heads are superb. That's why I'm not in favor of doing port work on them. From the mid-fifties on, virtually every engine design department did a lot of flow bench work on each new generation head. The beauty of die casting is, once you have something that really works, you can re-produce this in the millions. And the engine used in the Hawk is the beneficiary of this outstanding head design. Now, when some manufacturer has a frame and chassis he wants an engine for, they have a tendency to not understand the interplay between the intake system, the head and the exhaust system. Or, in engineering terminology, the effect of the interplay of these issuus on B.M.E.P.. Brake Mean Effective Pressure. How do you get more BMEP? Reduce to the minimum air flow restrictions on the intake side, and do everything you can to improve exhaust flow, and jet the carburetor accordingly. Next, if you want to spent the money, more compression ratio. The cam used in this engine is more than adequete to do the job. After all, the engine spins right on up to ignition cut off speed, so getting adequete cylinder filling at high rpm is not the problem, the problem is to get more bang for the buck, ie better BMEP, so you get some more bang per firing shot. Focus on this, and you will be sucessfull.

12-13-2016, 01:46 PM	#253
Ariel Red Hunter Join Date: Jun 2016 Location: akwesasne, NY-13655 Posts: 2,220	The Hawk And it's many brothers and sisters that use the same engine. Luckily for short money guys (like me), foundry technique had progressed to the point to when these engines were first built they already had superb head castings in mass production. Die cast aluminum heads started in the 1930's with radial aircraft engines. You can see, perhaps, the advantage of die cast heads from a production standpoint of engines that required 7 or 9 or 14 or 18 or even more identical heads per engine. By the time WW11 rolled around, die cast heads were in common use. And these were 2nd or 3rd generation heads. Which meant that the intake and exhaust ports were much more sophisticated. The big time manufacturers of the radial engine were Wright, Pratt & Whitney in the US, Bristol in England, and BMW in Germany. Not to forget radials used in Zeros in Japan. So, from this experience came the first die cast heads for motorcycles in the early 1950's in England and Germany. It took 2 or three generations of making die-cast heads in the MC Industry to really get the porting right. Honda did a superb job of designing heads by the sixties and beyond. So the head on the Hawk was perhaps a fifth generation design. And these heads are superb. That's why I'm not in favor of doing port work on them. From the mid-fifties on, virtually every engine design department did a lot of flow bench work on each new generation head. The beauty of die casting is, once you have something that really works, you can re-produce this in the millions. And the engine used in the Hawk is the beneficiary of this outstanding head design. Now, when some manufacturer has a frame and chassis he wants an engine for, they have a tendency to not understand the interplay between the intake system, the head and the exhaust system. Or, in engineering terminology, the effect of the interplay of these issuus on B.M.E.P.. Brake Mean Effective Pressure. How do you get more BMEP? Reduce to the minimum air flow restrictions on the intake side, and do everything you can to improve exhaust flow, and jet the carburetor accordingly. Next, if you want to spent the money, more compression ratio. The cam used in this engine is more than adequete to do the job. After all, the engine spins right on up to ignition cut off speed, so getting adequete cylinder filling at high rpm is not the problem, the problem is to get more bang for the buck, ie better BMEP, so you get some more bang per firing shot. Focus on this, and you will be sucessfull.
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