How much clearance should there be for the 3" pipe that goes over the rear axle? I am in the middle of installing a Magnaflow catback system on my 91 which needs slight modifications at the ypipe area. The cars factory catback is long gone and so is the factory flange after the cats so I have to make a custom pipe to bridge the gap. I just need to know what a good amount of clearance is for the pipe going over the axle.

The car is lowered with the Eibach Pro kit.

This is what I currently have for clearance.










Just not sure how far up the axle moves during suspension travel.

 

Looks can be deceiving but it looks like you have more clearance than my 3" pipe.
If it were me, I would unbolt the shocks and remove the springs. Jack the housing up to the stops to verify clearance.
It would drive me crazy having the exhaust hitting over bumps.

 

Yeah, what he said and the bump stops do compress a bit too. Put the axle to the bump stops and still give it 3/4" to a inch of space in between the two or more if you can.