Low frequencies on a 6.5" sub?

Would I be able to get low 40-90Hz sounds from a 6.5" sealed sub in a car? 
I'm looking to use my factory sub with a different amp with an adjustable 
crossover to turn the resonating frequency down from the 160-250Hz range
to 
the 50-90 range.  I'm looking for decent-quality sound without being 
"boomy."  Has anyone seen this done easily, or am I looking for too much
out 
of a 6.5" sub?  Would I need to go to 8, 10, 12 inches?  I'm not really 
willing to sacrifice trunk space for this project; I'd only retrofit an 
existing setup to the current spot where the stock speaker is.

Phil