This is the kit that I was looking at before I started this thread. I know my old pistons are domed and I like the light weight rotating assembly because of the quicker rev. and less stress. Is there anything I can do to the stock heads to make them better? I really want to keep the outside looking as stock as possible. Also if the assembly is balanced why have it re balanced before assembly, and what is up with two different rod lengths of 5.700" and 6.000"? Sorry if some of these questions sound stupid but I've never done a stroker engine before and I like to do as much of the work myself as possible.
Lets go through this a question at a time:
Anything you can do to lighten reciprocating weight is going to reduce stress on parts and allow faster reving. A hollow forged piston is lighter than a stock cast one because they have to be reinforced with a steel skirt and pin boss strengthening clip to allow the cast part to live under the conditions it is exposed to. The forged piston is strong enough without the added steel because of how it is made. A longer than the stock length 5.7" inch rod also lightens the reciprocating weight by making the compression height (distance between the center of the pin and the top of the piston) less. Less material less weight. Additionally a 6.00" inch long rod improves the rod angle (the angle piston makes with the crank throw to put more effort into forcing the piston down than pushing against the side of the cylinder: which goes back to trigonometry and the ratio of the sine of the angle).
Yes you can rework your stock heads for a modest improvement. Read David Vizard's excellent book on the subject:
The greatest improvement if your budget would allow it would be to buy a set of AFR 195 cc heads and have the ends milled in a CNC machine to replicate the ID casting marks of a stock Chevy head and then paint it orange
As to balance how balanced does it need to be? I balance my personal engines to plus or minus two grams (bear in mind you have to have confidence in your machinists as balancing is as much art as science). SCAT or Eagle says plus or minus five grams is good enough, and the factory back when these cars were new coming out of Detroit balanced their motors to a half an ounce (14 grams plus or minus) and they survived for 100,000 miles.
So why is balance so critical? For two reasons. Longevity of parts and making power. The higher you can rev a motor the more power per unit of time it will make (RPMs stands for revolutions per minute). At higher RPMs the bearings and rod bolts are being beaten to death. add an out of balance vibration and things get worse in a hurry. For street driven cars ±14 grams is good enough. Street strip I say you can get by with the ±5 grams. For a class competitive drag car or road racer you want the ± 2 grams.
Additionally how it is balanced is also critical at higher RPM's. Internally balanced means most of the balancing weight is inside the crankcase. With an externally balanced motor they hang the extra weight on the snout and the end of the crank that can cause the crank to flex. The higher the RPM the likely you are to hit a harmonic with the crank flexing causing the crank to fail.
I am a degreed mechanical engineer and have been building motors for decades (used to any way but old age has finally caught up with me). I read on my own (not part of my engineering curriculum)everything I could find on the theory behind designing engines. To be truthful my degree is in Industrial engineering so I had to additionally study the procedures involved in making engines from raw materials (taking it from Bauxite or iron ore to a finished product). I paid for my early racing career by working in heavy industry (using the companies machine or tool and die shops after hours to work on some of my motors along side master machinists because they knew more about machine tools and their proper use than I did).
Because of this I think I know how a motor works, and had a lot of good luck in racing (there is more to racing than having the most powerful engine by the way). Hope I clarified some things for you.