aintskeered,
These 2 engines are so similar but so different.
Of the similarities, they both respond VERY well to:
- better flowing exhaust
- headers
- a little extra compression
- lose the crank shaft driven fan and clutch
- tip top functional cooling system
To get more compression with the 2.9L, use Ford 2.8L flat top pistons and up to 0.035" mill on the heads.
To get the same compression improvements from the 4.0L (with up to 94 series heads), use Ford SOHC 4.0L flat top pistons and up to 0.035" mill on the heads.
Neither set up will require tuning if used with 94 or older computers (86 to 91 2.9L or 91-94 ohv 4.0L).
Both engines appreciate not spinning that archaic fan and clutch, using an electric fan or set of them instead.
Using a better flowing exhaust with headers and no crank driven fan and 100% stock engine made the passes a breeze with my 2.9L. The same engine rebuilt with a balanced bottom end, flat top pistons and flow bench port/polish heads/intakes, the overall driving experience was so much improved, that it's hard to explain in words.
I can assure you that rebuilding your 2.9L will cost less in the end as I have rebuilt both the 2.9L and am currently finishing up a 4.0L.
• The replacement parts for the 2.9L are REMARKABLY less expensive
• no rewiring needed
• the 2.9L will get better fuel economy than the 4.0L...no matter what
• for serious off road intensions, I am inclined to agree with Rusty, a built 302 or 5.0L can deliver a new plateau of power.
In summary,
* rebuilding a 2.9L with flat top pistons and a free flow exhaust without the crank shaft driven fan/clutch will be an incredible improvement. [25 to 33 mpg are reasonable]
* swapping in an ohv 4.0L will cost more, use more fuel and be require more effort but will provide more power and torque and a non adjustable valve train. [22 to 28 are conceivable]
- the primary reason I suggest this will cost more is to achieve the same level of reliability from the ohv 4.0L as the rebuilt 2.9L, it will also require a rebuild and subsequently use more fuel.
* a mid size truck/SUV with a stock v8 isn't much improvement but a BUILT V8 is a HUGE difference in power. I've never made more than 24 mpg from any V8.
Awesome post!
So when you rebuilt your 2.9, what did you do for block machining? Magnaflux I am sure, but what else? Line honing, deck leveling, etc? I am thinking of rebuilding a block I have laying around and I have a lot to learn.
As for offroading, it really depends on what you want to do. I wheel
a lot in fairly difficult terrain. I have the 2.9 BII and a 2.7 2015 Tacoma. I really have
never wished I had more horsepower. Now gearing, traction and line choice...
that is important. The only time I might want HP is trying to get through a mud hole, but even then, thats what my winch is for. If you want to rip tires up an obstacle, that's fine (and I get it), but all you are going to do is break stuff. If you are at that level, build a truggy or a rock bouncer. I go as slow as possible and as fast as necessary. High HP is just not needed for difficult-level average guy offroading IMHO. You do get better torque with those higher HP engines, but you can make up for all of that with gearing. I'll take a simple low HP engine, gearing and a doubler any day!
With all that said, V8s sound cool and I get it lol. Also, I bet a 302 at the end of the day would be more reliable long-term, but I am just guessing with that.