The weak link in this horsepower chain is exactly what you identified, Thomas, the cast pistons. For a later story with a Magnuson high-helix blower using E85, we replaced the stock cast, dished pistons with a set of Federal-Mogul flat-top forged pistons (PN 2491F 0.030-over). What makes this an even better choice is we found these pistons and a Federal-Mogul 11/416-inch ring set in a budget package (PN 8KL2491F30) for $349.95 through Summit Racing. These are flat-top pistons with two valve reliefs that will make roughly 10:1 compression when used with 64cc-chamber, Vortec, iron cylinder heads.
Once your engine is equipped with a good set of forged pistons, we can talk about getting aggressive with a simple yet effective plate nitrous system. As an alternative to the supercharger, all the nitrous companies offer affordable single-stage nitrous kits. We don't have the space to detail all the systems, so let's use a Nitrous Oxide Systems (NOS) Powershot system (PN 05001NOS, $373.95 summitracing.com) as an example. This kit is rated at between 100 and 150 hp, depending on the jetting. Or, you could step up to the next level with a Cheater system (PN 02001NOS, $475.95, summitracing.com) rated at between 150 and 250 hp.
The Cheater system is more expensive because it offers larger solenoids to flow more nitrous and fuel. We'd go with the larger system but start out with the smallest nitrous jet combination just to make sure everything works properly. You can step up to the larger jets later. Both kits come with a 10-pound bottle, but we would recommend going with the optional 15-pound bottle because you can burn through a 10-pound bottle pretty quickly.
Most current nitrous plates...
Most current nitrous plates use a multitude of holes in the nitrous tube to direct nitrous into the engine. At levels above 200 hp, it's best to use a single-plane manifold to take full advantage of all that power.
The horsepower ratings for most nitrous systems are actually pretty close. Before adding the blower, our 350 small-block Chevy made 411 lb-ft of torque at 4,200 and 368 hp at 5,400 rpm. Adding a 150hp nitrous kit to this combination should mean the little motor will make around 520 hp, which is roughly 75 peak horsepower more than the blower package. What's even more encouraging is what nitrous does to torque output. Let's just look at the normally aspirated torque peak number of 411 lb-ft at 4,200. Since nitrous flows through a fixed orifice, the same volume of nitrous is flowing at this lower engine speed. Using the formula tq = hp x 5,252 / rpm, we can calculate the torque increase of a 150hp nitrous shot at 4,200 rpm: tq = 150 x 5,252 / 4,200 = 187 lb-ft of torque increase. Adding 411 + 187 = 598 lb-ft of torque at 4,200 rpm. Think of this as an "advertised" torque gain-your actual number will probably be lower-but so what? "Only" 550 lb-ft of torque at this same rpm is 100 lb-ft more than the blower made at that same rpm. Just for fun, we plugged a 200hp shot into this equation and came up with a 250-lb-ft torque gain for 660 lb-ft of torque. Ooof-dah!
At this point, you have to be thinking, "What's the catch?" The answer is that nitrous is a consumable. In other words, a 15-pound bottle of that go-fast gas will last about five to six runs down the quarter-mile. Then you must refill the bottle at roughly $4 per pound. Assuming 12 pounds of nitrous to refill the bottle, you'll spend $48 plus tax. Let's say you're having a great time with your newfound power, refilling the bottle twice a month. That means you'll spend more than $1,100 per year in nitrous. Add that to the price of the Cheater system, and in one year, you've dropped $1,575. Compare that with the price of the Weiand blower at $2,130.39. There's the catch. While the initial cost of the supercharger is higher, it offers unlimited passes down the dragstrip-except for your fuel cost, obviously. But again, with nitrous, you are making more power. It all comes down to how fast you want to go. Part of the reason nitrous makes more power than the blower is that the blower must expend something like 25 to perhaps 35 crankshaft horsepower to drive the blower, especially at higher boost levels. The bigger the blower, the more power it makes, but also the more horsepower it eats. That's the beauty of a turbocharger, which relies on exhaust heat and pressure to spin the turbo. Because it is not crankdriven, there is only a small penalty in exhaust gas back-pressure, but this equates to a minimal power penalty.
As for your question on torque converters, given the major torque boost you're going to gain with the nitrous, you won't need a very high stall-speed converter, since the torque gain will radically increase acceleration once you hit the button. Traction will actually be your biggest problem. We'd suggest a torque converter with a relatively mild stall speed of around 2,200 rpm, but one designed to take the abuse of the additional torque. Also keep in mind that if you actually hook all this torque to the ground with sticky tires and at least a limited-slip in the differential, nitrous will quickly uncover the weak link in your drivetrain. This is going to require a stronger rear axle assembly and driveshaft.