Hi,

Is it possible to cure prepregs that are supposed to be used in an autoclave using an oven? The manufacturer recommends 85 psi of autoclave pressure and 177 degrees C temperatures for curing and I'm wondering how critical the pressure is to achieve good results. 

I think Steve is on to something.  The resin viscosity is temperature related, so if you can get to the right curing temperatures then you should be ok.  Unless the resin is very high viscosity and needs the pressure (unlikely) then you should be fine.  Debulking will be the most important factor in laminate porosity.  Increasing the "dwell" at 80C to an hour or more (especially with a heavy tool or with core) will allow the resin to "flow" more before the curing process starts.  

If you have surface issues, try a "hot debulk" of the first two layers.  Just bag them (I like to leave the backer on, spiky roll it, and cover with infusion flow-mesh) and heat under vacuum bag to 60C or so - enough to make the resin flow but not cure.  You only need maybe half an hour of this debulking - not sure where the 8 hours they recommend came from.  If you are making a part with many layers, try to repeat the debulking procedure every 1000g of material or so.  Lack of debulking and slip joints are two areas where prepreg lamination can go off the rails.

Mold finish also effects surface porosity a lot - which is why the same process in a polished aluminum mold will look better than in a composite mold sanded to 320 grit.  Adhesive teflon is great for this for one-off molds because it has very low surface tension.  

Moisture can be a real problem especially if the prepreg is unwrapped cold and condensation forms on it.  This is why is is always key to store prepreg in a sealed bag and to defrost it to room temperature while it is still in the sealed bag - the condensation forms on the bag, not the material.