Is it worth the time and expence building heads with bigger intake and exhaust ports ? And by extention high flow manifold and larger injectors .
My goal is to have a gain of 15-20% increase in hp/torq so the tranny and transfer case will not need any mods , but remain within the safe level of usability . any input to help my 3.9 .

 

I would say go for it. but you need a cam out of the early 4.6 motor to take full advantage of porting the heads. But usually porting the heads increases HP but lowers your torque. Just remeber these trucks are a brick not a race car

 

As well as a set of headers and new, heavier valve springs.
Is it worth it, I don't think so, but some people do it anyway.

 

These engines have plenty of HP and low end torque for off roading IMHO so I don't know why you would want to mess with all that work. But to each his own. I realize they are not real quick off the line but I also have a 4 banger Jeep TJ so the Disco is like a race car compared to it lol. I would put that money to better use on something like lockers and a winch if I were you. If you are unhappy with the highway get up and go, then I would just look for another vehicle. You gotta realize they are made for one thing, off road use. And that my friend they do great with very little modification. Again to each his own. Good luck with your rig and enjoy it!

 

I would suggest just doing a cam with a larger rise and porting the heads. Then stuff some headers in....

But if you are wanting to fab, go at it...

 

I realize that more power is mostly a pipe dream with rovers. But many people get slammed for asking how to get more power. Maybe it comes down to why you want more power.

Cruising down the interstate at X-mph and off-road, I feel it is more than adequete.

BUT, hook up a 2k lb trailer. Totally diff. story. Forget holdin 65 on the slightest uphill grade, or sometimes even 55. Sad to say, but my GF's windstar will out tow my Disco.

 

Thanks . springs , shocks and driveline instead . 2in lift . thanks, Endshock

 

The best power adder will cost you $4K for a 4.6. You have to find a distributor drive engine, and anything after 96 will be direct ignition...

You are on the right path with suspension work. You can spend plenty there...