The following post is stolen from here. "For those of you looking for more technical data on these coil packs, here is what we've found so far with our bench ( oscilloscope ) testing: 1) These coils can be used on your FSI/TSI engine at ANY level of modification. They function just as well on a dead stock car as a highly modified one. 2) They are NOT the same coils with red housings. The secondary circuit on the R8 coils has a higher resistance (more windings) than the stock coils. In fact the secondary circuits were slightly closer to the Okadas we tested than the secondary of the stock coils. 3) We tested these between 12 and 16 volts (remember if your alternator is charging properly the input will be right around 14). We tested them between 200 and 16,000rpm. The stock coils started to misfire at a much lower rpm than the R8's with a stock spark plug gapped @ .032". 4) The spark was visibly brighter and more intense on the R8's when compared to the stock coils @ every rpm we compared in the stock rev range. We didn't compare anything under 1,000rpm. 5) We were able to open the gap on the plugs much further with the R8's than the stock plug with out misfiring at the same rpm/voltage. 6) Here is what we were finding as an AVERAGE on the secondary circuit for each of the coils. Stock: 3.3 M ohms < refers to stock audi coils R8's: 5.31 M ohms" Still looking for more details on the actual voltage, but the 60% increase in resistance implies that the coils are have a lot more windings, ie a much higher voltage.