port size?

what size port do you think would be the best. 

The box is 1.21ft3 for a single kicker comp vr 10.  I'm not sure what size port to use.  i have built this box before and used a 2" port tuned to 30 hz but it didn't have enough backpressure and the sub bottomed out a lot.  Now i am thinking about a 1.5" port tuned to 30 hz. i haven't been able to find any info or general rules of thumb  on port size compared to sub size.  I have heard before that for 12's and 15's don't use anything smaller than 2" but i've never heard anything about 10's.  any advice would be appreciated.

4" seems a little big for a single 10 don't you think

In a 1.21 cuft enclosure, 4" will require too long a port (28" approx.)  If you really want to try and port that small an enclosure, I suggect using 2.5" diameter at 10" long.  It will have lots of port noise, though.  A larger enclosure size and a larger port would probably work better.

Well, whoever told you that was... err, wrong.

Your Kicker Comp VR10 requires a vented enclosure size between 1.25 and 1.75 CUFT with a rather large slot port.  When vented, it is rated at only 200 watts RMS.  The preferred mounting for these wooferes is in a 0.8 CUFT sealed enclosure, and when sealed it can handle up to 300 watts RMS.  So, if you must stay at 1.25 CUFT, I recomend you remove the round vent and either seal up the enclosure, or rebiuld it with the recomended 2" X 10.5" X 20" slot port.  HERE's your owners manual with recomended enclosure information.  Your amp is too large for this woofer, and you will need to add a subsonic filter (your Kenwood does not have one) at around 30Hz.