Well, on this chart

8.7 13.5

An 8.7 1/8 is about a 13.5 1/4. . roughly.. other charts list it at 13.7. Your takeoff seemed to _ME_ to be a tad slow.

Again, you're calculating with unknowns here twice..

But if a 8.7 1/4 is _ROUGHLY_ a 13.5, assuming all things are equal..

a 3500 pound vehicle that does a 13.5 in a 1/4 has roughly 285hp to the wheels, while a 13.7 is roughly 273hp to the wheels.

I doubt this really accurate, but possibly in the same ballfield. I used 2 charts to translate your 8.7 to 13.5 or 13.7.. and then there's all kinds of calculators that translate ET time + weight to power.

Hope this helps,