Sorry you had to wait this long, I am on jury duty right now, but have time strating in the evenings. Actually both heads are good after the combustion chambers are reworked. The G head is the bathtub design and both the valves are in a jellybean shaped cavern. The advantage is the raised compression of about 1/2 a point over the 782 fast burn head, the disadvantage or actually improvement that is needed is the edge and sides of the cavern is fairly straight up and down and needs to be flared or widened to allow the valves to breathe better, the almost straight sides mean the flow at .100 inch lift does not greatly increase as the valves open, the shrouding from the sides going (almost) straight up restricts the flow for greater power with greater lift. By flaring the sides a little more, the lift of the valve has more room to suck from the open valve and move outward, also, as the spark starts, straighter sides tends to push the flame from the sparkplug inside the cavern and against the piston top, but then burns residual gasses left over after the piston is lower in the bore, a spark and a flared side cavern tends to move the gas towards the piston and expand outward, burning faster with the piston higher, thus more power. Taking the sharp edge of the cavern and rounding it really increases this flame travel, and as we all know, the higher the compression when the fuel/air burns, the more power is made and the more torque produced. This also reduces the amount of coking of the quench areas because the fuel that hangs around the surface of the quench areas is burned hotter at a higher compression (piston up farther in the bore) and remains cleaner, and I mean really clean. Last time I did this to this style of head, 20,000 miles looked as clean as a head that was run to break it in and then pulled. You don't scrape the coked junk off the head to clean it, you take a wire brush and hand clean it she burns so clean. At the same time, without doing this, pull an old G head off and you will find the quench pads are black and a burned crust that has to be scraped off.
The 782 head is heart shaped with the quench pad going around one side of the intake and exhaust opposite the spark plug firing. The quench pad, being heart shaped, wraps around the intake and exhaust, the top curve of the heart shape actually sticks between the intake and exhaust valves, so shrouding is really great and since this shroud/quench pad is again, straight up and down, open the intake and exhaust valve .500 inch, the shroud comes flat with the top of the valve face. If you can stick your finger inside the open valve area you are pushing it, the idea of having a valve only flow out one side of an open valve into a cylinder, might as well just have a smaller valve to begin with, and they also then say don't touch the exhaust valve, porting the pocket doesn't do any good and can actually cause more problems and reduced flow. It isn't the E valve pocket that is the problem it is the fact the head wraps around the valve from the center of the chamber to the whole opposite side and port all day long, if this is the same, no change will occur. Again, curve these quench pad/shrouding away from the valves, intake and exhaust, all the way around, so that as the valve lift increases the distance from the valve edge to the quench pad/shroud area the more flow the head will have pure and simple. The 782 head tends to coke up on the quench area and top of the valves because of the shrouding, and clean fuel streaks tend to move out of the small area the valve opens, both of which are because the head is sucking so much into the cylinder from the small flow cross section the fuel keeps the head surface fuel washed and this should not happen. Now, when the fuel/air burns, again, the curved quench area will keep this area clean and power increases the same way. Several years back I had a three hour phone conversation with mpgmike about the porting requirements to increase chamber flow and cleaner burning and I am sure one of his porting heads article shows pictures of what I taught him, his pictures were pretty good from what I remember, so you can look at them, this explains what to do, sometimes pictures help. Now, a person may say it drops compression. Yes, it does, at a rate of one tenth to two tenths, and still the power gained outweights the loss of compression, and, at the same time, you take these head designs up to compressions of 11-12:1 and you can still run 87 octane without a single pinging issue in otherwise stock condition and equipment (including smog requirements) and laugh at the numbers they are so low. Drop a turbo on this head design and there was one person that said he was able to reduce his boost by half and still run the same times in the quarter mile. That translates to quite an improvement and things lasting longer, which is the whole idea, right? Another cool thing about this is, mileage is not hurt and will usually go up, and for those that remain the same, mileage tends to increase at higher rpm over stock. Case in point, I ported and chambered the head on the 2.4 in my PT Cruiser. I drove 1250 miles one way, 65mph got me 29mpg, 75mph got me 26mph and 80-85mph got me 24.5miles. Ported and chambered the head and 65mph got me 30mph, 65mph got me 30mpg, 75 and above never went below 28.5mpg, and I was able to climb and make it through the mountians in fifth gear without bogging as long as I started out at 65mph, before ported it had to be 75mph to do the same thing. Lots of advantages in fixing the combustion process under pressure I say.
Edit add: When I talk about flaring the sides of the G or 782, the idea is that as the valve opens, the distance from the valve edge to the shrouded area, the gap increases up to the point the flare is to the size of the head gasket ring (more is not good).
