5 inch...... look at this way........ you can always grow in to it....... no matter how big the turbo you will get. the exhaust will be done. and you wont have to buy another exhaust.. just my 2 cents
Some guys say you lose hp when you put 5" on a truck that makes less than 500hp. But in my personal experiences, I can't tell any difference in the SOP meter. Even though 4" is big enough, 5" sounds way better.
5 inch exhaust on a truck that has a stock charger will cost you HP and raise your torque.Reason is that the sheer size of the tubing allows the exhaust to cool inside the pipe and disrupts the flow somewhat.On back to back pulls with my truck when I had the HX35 on it I lost 17hp and gained 100ft lbs during a October dyno test.I did that as I had a steak riding on a bet that I would not loose anything which I did and lost the steak too....Andy