I used an el cheapo oil pan as a starting point for my dry sump system. When I was happy that the shape fit the requirements I took a mold of it. This was in 2003 and the mold sat on the part for a few years. Some of what I write here may help some of you that don't have experience working with composites. This mold is for a one off item so I felt that using an expensive epoxy system was a waste. I used Polyester instead.This system shrinks between two and five percent as quoted by the manufacturer but experience will say different. If you're eyeballing the amount of catalyst(hardener) you're using you won't get a good result. The best thing to get for any type of fiberglass work is a digital scale. It's the most important tool for working with composites. Your ratios will be spot on and you won't have problems with exotherm which is the cause of shrinkage and warping of the finished product. When I built this mold I used woven glass fabric because it gives a stronger finished product at a reduced cost. Chopped strand is junk and I call it the resin thief because it just gobbles up product and due to it's thickness it does create more heat when curing. In my experience the cost is about one third by using the woven glass. If you're in a hurry composites are not for you, this takes patience and I leave Polyester parts in a mold for a minimum of three days but typically for a week or more and I build up the layers only a few at a time. I get no visible shrinkage. When I eventually pulled the mold off the pan it only needed a light polish so the gardener at the time volunteered due to the rain we had that day. He spent a few hours on it and it came out great. He was born to polish, a part of the process I hate more than death.
A few weeks ago I produced the finished product. It's about 8 layers of Carbon using my own blended resin that can handle 200c for 8 hours or 140 indefinitely. I went through all the usual steps and got it into a vacuum bag to consolidate the piece. The only tricky part is when you actually pull vacuum. This resin has a very short pot life but you can't go to soon either. Many years ago when I was young and dumb I panicked and pulled vacuum too soon. I ended up with resin in the connectors, the pipes and the vacuum pump. That clean up was horrendous. Never again. Now, I leave a little resin in the mixing bucket and as soon as I see the viscosity change I connect the pump. Another tip on cleaning brushes is that you don't need to soak them in Acetone. Use the edge of the mixing bucket to scrape off as much excess resin as you can followed by a pull through an old rag. You then soak the brush in a container full of a mix of washing powder and warm water making sure you stipple the brush vigorously. I leave the brush in the solution for an hour or so and then rinse off. This only works with Polyester resin though. In some cases you might want to use some Acetone to finish the job if the brush is a little hard after drying. The oil pan came out of the mold needing hardly any finishing but because the mold is a female the rough side is actually the surface that mates to the engine block. Easy fix, I layed up two strips of 4 layers of Carbon on a sheet of thick glass that had been pre released and placed the pan on that using some lead weights for added pressure. The pics are moblie phone examples so the quality is iffy but this is one strong part. I hope you got something out of this post.