i am finishing up a top-end rebuild and have no spark, trouble-shot down to the coil itself, but have been having a discussion with a coworker in regards to the amount of voltage needed for my tpi... i've been running an msd distrib, coil, and wires for a long time just as an upgrade, but the only "mods" are a larger cam and 3-angle valve job, really. i don't know what the output is on a stock coil, if it's the same/more/less than something aftermarket, but my intent was to just replace it with another msd coil. what my real question is, is if a more powerful coil is needed with a larger cam or not. was just wondering... at this point, plan is just to replace with same type coil.