whats the difference between high impedance and low ???
High Imp. are called "saturated" injectors, while Low Imp. are called "Peak and Hold" Injectors. Saturated injectors fire with about 1 amp of current, and are held open with about 1 amp of current. Peak and Hold Inj. have a much beefier coil, and are fired at 4-5 amps, and then within a couple ms of opening, are reduced to one amp. Effectively, they Open MUCH faster, they are prevented from overheating during static conditions by the 1 amp "hold" driver, and also close faster because they are less susceptible to being slowed during closing by electromagnetic induction due to their low hold-open current. generally larger injectors will be of the P&H variety.
P&H injectors can be run in a saturated circuit by using resistors, but they effectively become Saturated injectors as such, and have no P&H properties... in some cases, they may be slower than a true saturated injector. Saturated injectors can also be run in a P&H circuit, but their P&H functions are greatly reduced as they have their own internal high-resistance, preventing a full 4-5 amp firing. They may gain a little speed by way of the current reduction, but thats about it.
Generally, its best to stick with the correct injector, resistors are just a cost-cutting measure as P&H are generally cheaper to buy in high-flow injectors. If you REALLY need a HUGE injector (over 60-70 lbs), get a true P&H driver, and run them correctly. There are excellent P&H drivers on the market that will turn saturated signals into a true 4-1 P&H signal, and make sub-1ms injector firing possible. For example, a stock saturated Viper injector idles at about 6-8ms. I have run 96lb P&H injectors on an SRT w/a P&H driver at full fuel system pressure, idling at ~.8ms without a problem. (also note, the rough calculation is 3x the injector size, but the pulse is about 1/10 that of the saturated injector- thats how much faster a P&H responds than a saturated. A saturated injector run at .8ms would not even open fully if at all, thats why idle quality would be so horrible.)
The tuner took these out and replaced with 650cc's. That's all I know. I'm not very mechanically minded. They have about 3,000 miles on them.
