[decooney]

Buzz,
I would not consider a Kirkham IRS in the same lower league as a stock Jag posi differential used as standard in the Unique or ERA. Apples and Oranges. Lighting up street tires and doing doughnuts is not the same as launching on a 1/4 mile launchpad surface. Without even trying, I broke the 1/2 shafts, stub axles, and/or differential in my Unique and my ERA Cobras, both of them. The stock Jag IRS is not designed to handle it for long, and one can try it until it breaks. I have a few other friends who experienced the exact same. Neither of these cars will withstand much like a Kirkham differential and IRS system will in my opinion. Not a relative IRS durability comparison if you ask me, and a hard lesson learned after proving the results twice, ugh. BTW: I've launched plenty of muscle cars and pro street drag cars with Ford 9", GM 12 bolt and even weak 10 bolt rears with no problems. Seems it really takes a well engineered and durable IRS "system" to expect it to last before the weak link gives out. Even though I upgraded my Jag/Dana IRS setup with a wheel hop system, upgraded differential gears and internals, and better shocks, I still would not recommend or consider a moderate to hard launch in an ERA or Unique (with a non-upgraded stock Jag differential, stock axle IRS setup) and motor at 400hp+ at this point. i.e. just not designed for it.