i build a large size model of a part of car (chassis) using Pro/engineer then i save it in *.igs form.
I tried to import the igs model using ANSYS.
i did' nt succed (memory size problem ...).
You could try breaking model into smaller chunks and importing each of the chunks seperately. Then glue them together once imported into Ansys.
Igs translations are generally not very successful when trying to import complex geometry into Ansys. You could try getting a "demo" version of the ProE connection product from your Ansys dealer and importing the geometry that way.
What type of elements are you planning to use to model the chassis? If you can use shell elements, then you can reduce your cad model to the "midsufaces" of the chassis components, which should cut down the size of your igs file.