Since gears are torque multipliers, and the rear tires are getting more power delivered to them
This is false. Gears don't affect power, they affect TORQUE. Power, AT BEST, can only remain the same through a gear change. In reality, you'll almost always see less power with a change to numerically higher gears. This is easily verified on a dyno, and is not a freak effect of dynos-it's real. The reason for this is what I said before-the numerically higher gears require the engine/drivetrain to accelerate quicker for any given amount of vehicle speed increase. The extra power required to produce this increased driveline acceleration shows up as a decrease in available power at the wheels.
Now, you may be thinking "that can't be right-people almost always go quicker with more gear" and you're often right. The reality is that BOTH things are true, as weird as it may sound. How this can be is that two opposing factors are usually at work here-one is the tendency to get less power at the wheels with more gear, and the other is MOST cars' need for more gear than they already have, purely from an acceleration standpoint. On the average car, the improvement from more gear outweighs the power loss-hence, the improvement in ET. It may sound like I have contradicted myself-I just said that most cars need more gear for best acceleration, but I also said more gear decreases wheel hp. How can this be? Again, it's opposing factors at work. The average car is geared for many factors other than just acceleration (which is a good thing-don't need to make the mideast any more money than we already do). To produce a good ET, you need to select gears that will cause the engine to operate at as much as possible at speeds where it produces as much power as it can. This is usually at the higher end of the rpm range with a gasoline engine. A numerically low gear won't allow the engine to rev to that rpm quickly enough for good acceleration. Conversely, too much gear will require the engine to spend too much of it's own power accelerating itself, and the rest of the drivetrain to boot. It becomes finding the best BALANCE between these factors. Where that balance falls is what determines the best gearing for acceleration.
I realize that I just said something else apparently contradictory-that lots of gear allows engines to rev to the rpms where they make the most power, but also costs power. The answer is that again, it's a balancing act. It's a balance between having enough gear to let the engine reach high rpm relatively quickly, without making it spend too much power accelerating. If you put 5.38's in there and make it rev almost instantly, you lose power. If you put 2.14's in there and keep it from ever revving enough to make power, you lose power. See? Opposing forces again, and again it's the BALANCE of these factors that determines best acceleration. You could say that the best gear ratio (ignoring traction issues) is the one that strikes the best balance and allows the most AVERAGE power to be delivered to the wheels during a pass down the track.
The main point I'm making here is to point out that there are factors at work in gear selection that oppose each other, and that you cannot simply take the position that more is always better and expect to come out ahead. Many people do not have the option or ability to make their car hook with 5.13 gears, or build their engine such that it can safely and efficiently rev to 7500 rpm. From a theoretical standpoint it may be best if they do that, but reality often makes us compromise. When you have to make do with an engine that only revs to 5500 rpm, less gear than all-out drag racing gears is generally best.
Now, in the case of my car with the 3.91's and 4.56's...it actually hooked fine with the 4.56's. There was no tire spin, as evidenced by several witnesses. I had jet extensions in the rear float bowl, and the float levels were set properly for the track, so there was no fuel starvation or flooding problem. It's simply that somewhere in between 3.91's and 4.56's the car crossed the point where having more gear helped enough to offset the increased driveline acceleration. It is very possible that 4.10's or 4.30's might have been optimal, and therefore better than 3.91's. I did not have those gears to experiment with, so I simply put the 3.91's back in.
