My exhaust goes under the rear axle on my FWD. The problem with going over the axle is the limited amount of space. Most people say you can't even fit a 3" pipe over the top. As far as I know there isn't any exhaust made by any manufacturer that goes under the axle. I custom made my exhaust using autozone piping. Yeah it's not mandral bent but it only cost me $90 to make and I'm still making the same power as other's with the same setup. (375whp-365wtq with s16g)
Basically my exhaust has only two 90 degree bends and one 45 degree to go under the axle. I have about 2-3 inches clearance under the axle and not once has it ever given me any clearance issues. The only problem with it is when you lift the car on a lift and the rear axle tries to come down but the one side hits the exhaust and doesnt allow full suspension travel on that side. Basically you can make a flange so you can drop the axle-back portion anytime..
Here is a pic of when I was putting it all together:
3 inch til it goes under the axle and then reduces down to 2.5 to mate with my 2.5 magnaflow muffler. Eventually I'll be drilling it out to 3 but I'm not too worried about it right now.
Also I'm pretty sure there are only 3 guys with FWD 1g's on this site. Me, you and carlton I believe his name is.
Here's a pic somewhat showing it going under the axle.
