i agree but one of the varibles of engine durablity is comp ratio. what do you think is going to last longer a 6.5 running 15 psi of boost at 25.1 comp ratio or a 6.5 running the same amount of boost at 16.1. i rest my case

 

Neither, both won't last long at all without major internal reworking.

What case? That the 6.5 is weak no matter what?
My little 3.0L made more HP/L stock a decade prior to the 6.5's design and can make more HP/TQ than a heavily modified 6.5 by add only a larger injection pump and turbo. While you're spending $12k and completely rebuilding/reconfiguring the engine inside and out just to get 300hp, I need just to bolt on two parts to get that out of my 25 year old unopened engine.
The only reason I bother with the 6.5 is there are some tuning/modification techniques that can be translated over seeing as they're a "similar" design.

 

ok

 

Your both right, but, it is easier and safer to run high boost on lower comp ratios. The 6.5 at 16 will last much longer than one at 21.1, assuming the same modifications, other than comp ratio.

Think about this, push 15 pounds in to a 16 and a 21.1, thats 240 and 316 psi, in your cylinder head respectively. Thats almost 80 pounds more force that the cylinder head/piston rings have to hold back per power stroke.

Lower comp ratios are easier to run high boost numbers. Strengthen the block with a stud girdle, fire ring and head stud it and you would be good to go. Honestly on an indirect injection motor, 16 compression is too low, unless you live on the equator...

My .02