3p141592654;1973032 said:
If the alternator stays the same size, more amps = less voltage at a given shaft speed. No way around it. Then there's the car wiring to the alternator.... what current do you think its designed for?
Not entirely true, since it isn't shaft speed that (entirely) determines the alternator output, but the strength of the magnetic fields in the stator allowed by the regulator, or else the voltage would rise out of control if you drove at high RPM without first turning on enough electrical accessories. However to create more amperage at the same voltage means more power produced, which means more power goes into the process. Well, since the voltage regulator determines voltage, then you cannot get more amps at less volts, so at the same size, the alternator can only do what it can do. If you change the windings, you can get more amperes at the same voltage, just with the higher cost. It also means more parasitic losses at lower power, shorter lifespan of the components in the voltage regulator, diode trio and ultimately the windings in the rotor and stator themselves. Also greater strain on the spindle bearings, but that's probably the least of the increased trouble. It was worthwhile to me to run the high output (At low RPM) alternator while my car was an IASCA SQ car. I pulled that alternator and replaced it with stock when I stopped competing, and noted an immediate and measureable increase in fuel economy. I didn't put it on a dyno, but I'd bet on a corresponding increase in RWHP.
Call me crazy, but the first step should REALLY be determining if you're having a charging system problem. It's simple, really. Put a voltage gauge on the system, and unless you're dropping below about 13.5V at 2000+ RPM, (and your battery is actually known good) your alternator isn't a problem.
As to the fan... It also takes power to move air. Yes, fan design can make a difference, but it comes down to putting power to the air to move it through the radiator. That power comes mostly from forward motion of the car, but when the car isn't moving fast, it comes from the fan blades. Now we can either take some straight from the already created mechanical power (In the case of the 7M, from a belt driven by the crankshaft, the 1JZ, from a fluid pump) or we can take it from electrical power, converted into mechanical power by a motor. But that electrical power comes from somewhere, in this case, the alternator, which converts the belt-driven mechanical power into electrical power. These conversions are lossy, both ways, meaning for the SAME AMOUNT of mechanical power put into the fan blades, thus into moving air, the electrical fan MUST draw MORE power from the crankshaft, if both are to perform the same task. We cannae change the laws of physics, Cap'n.
So, either the fan takes the same, or less power from the crankshaft, but moves less air, or it takes more power to do (maybe) the same work. Given that overheating is an issue with the 7M, I'd take the better cooling system
