need help with port

The new box I have is supposed to be tuned to 35hz,but I think it might be tuned to 53hz.The dimensions are:17.5x12.5x34.5.The port dim. is 4x10x7.25.The box is made of 3/4 mdf and my speaker disp. is .06 per sub and I have 3.I came up with 3.36cu - .18cu(speaker disp.)=3.18 Then 3.18-.17(port disp.)=3.01
When I punch this into the12volt.com slot port calc,it says the box is tuned to 53.5hz.I just want to know if this is correct and if it is I want to know how to tune down to 35hz.When I play around with the port sizes 4x3.55x7.25 put me at 35hz.Any help is appreciated.

 

Any help is better than no help.

 

Thanks for the help.The problem is the box is already done.Having the 4x10x7.25(inside dim.)port,I was hoping to make the port smaller.The bottom of the port is also the bottom of the box so I thought that maybe I could screw through the bottom and make it smaller.If I take 3 pieces of 3/4 mdf 10x7.25 and screw together and then from bottom,I would have a 10x1.75x7.25 and that would put me at 38.3hz?What would you do?I really don't want to make another box.

 

So how would I do that?The port now is a rectangle.Sorry for the dumb questions,I'm just not getting it.

 

If I need to make a new box,than so be it.I drive a 1999 pontiac grand prix 2dr coupe.I think 40" wide is max,17.5" tall is max,maybe 16" deep but idk.I was thinking 35hz because that's what the manual says.The manual also says 1cu per,but somebody else told me 1.5cu per.Any sugg?

 

Thanks for the advice.The box is glued and screwed together,so I figured I will cut the face off(from the sub side),make the port changes,and then put a new face on and just recut holes for port and woofers.I just have to mark the where the old screws are so I don't try to screw into them.