what the most compression you can ran on pump gas with out running into any problems?IM lookin to get a rotating assembly from combo motors and he said with -5cc srp pistons and my lt-4 heads i would be at 11.5 comp,what do you think is that to much?

 

that would be ok if you run a cam with lots of overlap to bleed off cylinder pressure

 

With the camshafts LTx guys normally run, I wouldn't anticipate issues provided the tuning was decent. With a new shortblock altering static compression isn't too big a deal, so you could always back down to 11:1 if you really wanted to.

A search on the topic of Dynamic Compression Ratio may be of some interest to you - there have been some excellent threads on this site regarding static & dynamic compression ratios .