I have been around Ford products my whole life and right now I own 3 Ford vehicles. My recent purchase is a 1996 Ranger 4X4 EXT. Cab,4.0L-5-SPEED. The truck is great, but it needs a little more power. I have a 1990 Mustang 5.0L with MAC headers,MAC X-PIPE and Flowmaster 40 series mufflers. Also I advanced the timing 4 degrees and installed a K&N air filter and removed the silencer. My question is will the 1996 4.0L 6CYL. Run without cat's like the 50.L ? We have no emmissions tests here so cat's are not required. Right now I am looking at changing the exhaust system,inslalling a K&N intake system and running synthetic fluids. I have never owned a Ford with a 6 CYL. engine so I need help! Long live Ford power and my other 2 Ford's are a 1969 Torino Cobra 428CJ-4SPEED!!!!!....AN AWESOME ORIGINAL R CODE CAR, and a really clean 1978 F-150 4X4 with a 429 V-8. Thanks,and I look forward to hearing some info on my 4.0L Ford 6 cylinder engine mod's.

 

I don't have a 4.0, but when I got the exhaust replaced on the 3.0 Aerostar I thought the listing showed the same replacement exhaust for the 3.0 as the 4.0. If that is true then the stock exaust on the 4.0 would be pretty restrictive. I'd start with a free flowing exhaust--probably cat back--and see how that does. Then think about the intake side. But I'd say exhaust is far more critical to open up. Opening up the intake benefits mainly at wide open throttle and at higher rpms since at part throttle the throttle plate will be the major restriction, but opening up the exhaust benefits at all speeds, part and full throttle.

Oh yeah, I think we are in the 4 cylinder engine forum and you might want to post this in the appropriate V6 forum for better input by folks who actually have modified these engines.