Got a starter out there with my N/A 408...

I just got my 408 running, but getting the engine to turn over is quite a struggle for my starter/battery. Me and my uncle put it together...it's got around 6-7 thou piston to wall clearance and around 2 thou for the bearings. It's also got around 10.9:1 compression. The starter I'm using is from an 87 302 Mustang and the battery is an Optima red top with I think 850 CCA, which I would think would be enough. Anyway...like I said, the starter/battery seems to have a really hard time turning it all over. Is this a common problem with high compression 351W strokers? The battery with a fully charge only has enough juice for 2, maybe 3 starts one after the other before it's dead again, and this battery is definately still good.

A local guy thinks we built the motor too tight, but from what I've read, those clearances should be pretty close to what we want. I think maybe I need a high torque mini starter, because maybe that old starter just cant handle the extra 2 points of compression and 1" of stroke combined with the new bearings, rings etc.

Need some second opinions on this please...any input would be appreciated.


*edit*...sorry for the messed up title of this post, haha.