So, you're heading down a very strange and obscure road with building a Cologne V6. The 2.6/2.9l is one of the strangest animals in the family. Ill help as much as I can, as there is very little out there on them. But, they definately come into their own once you get your hands dirty with them.
With the exception of the 4.0 OHV, colognes generally need to rev in order to produce power. The 2.9.in your truck is probably the worst offender for this, and with some modification is very happy to scream its lungs out - if you spring for ARP rod bolts and shot peened and deburred factory rods, 6500 is a comfortable red line for them, forged rods and some other valvetrain work lets them redline to 7000 rpm. Not bad for an ancient v6. Keep in mind though, they're very different from a typical truck engine, as they are not, and were never intended to be a truck engine.
Fun fact, Cologne pattern engines are still around to this day, even though their production run ended in 2011. The ones produced today are now V8s and V12s, and wear Aston Martin badges across their valve covers (their 1000hp V12 is essentially two 2.9s staple gunned together in the middle). The potential for power is there.
If you want to see the ultimate Cologne engine, look up the 2.9 Cosworth. They easily put down 300HP naturally aspirated when modified, and 500-600HP when sporting twin turbos (on177 cubic inches, mind you). The cosworth version is your block with 24 valve heads. If you're a racing fan, they were designed by Brian Hart as a formula engine.
How much power you can produce is dependent on money and time, and what you would want out of it in the end. Where the thinking on these engines is a little backward is that this isnt as simple as tossing an RV cam in and sending it like most american engines. The 2.9 is a strangled Euro V6 when its in American form - restrictive heads, restrictive intakes, and exhaust manifolds that were designed by satan himself. The 4.0 OHV behaves much more like an american v8. The 2.9 is its faster, louder, revvier older brother. So, in my case, i wanted revs over low end grunt, so i stayed 2.9. 4.0 ohv will always deliver more on the low end, but is nowhere as capable on the high end as its thick walled short stroke cousin.
Some low hanging fruit for performance:
3g alternator swap
electric fan
headers
EPAS or Mazda electric power steering (you will hate Saginaw pumps after.driving an EPAS modified ranger)
Pre-86 throttle body,
gasket match porting your intakes
2.5 inch exhaust
modifying your air box
Head porting
Valve job
New lifters
High volume oil pump
Merkur/Granada twin throttle body intake swap
Electric water pump
Catch can
I could go all day. I wont.
Mine has been built to accomodate an Eaton M62 blower. Blower isn't on yet, but is ready to bolt up (work and a Honda accord have been stealing my soul). At this point, im running an aftermarket PCM (Megasquirt) along with a massive list of modifications, and I have methanol spray (washer fluid works well) kick in for when the engine is working hard and at high rpm). There are only two people I know of that have built a turbocharged 2.9, one of them
@DCinDC is a member here and drops by on occasion.
If you're wanting to stay naturally aspirated, a 200HP 2.9 is easy to build using 2.8 flat top pistons and a regrind cam.
If your motor is otherwise healthy, I'd start by cleaning. Colognes HATE dirt. They hate sludge even more.
No. Seriously. Colognes have two achilles - improper cooling and dirt/sludge. Both spell an imminent death, even with the improved heads.
Have you pulled your valve covers and intakes yet? 2.9 intakes are rather convoluted, and tend.to fill with pcv junk, and rocker shafts tend to plug with sludge.
The only injector and carbon cleaners ill use nowadays are Liqui Moly Jectron and their intake valve cleaner. I'd avise running both. Also, consider switching to Liqui Moly synthetic oil (or regular synthetic with a can of their MoS2) or something with a high ZDDP count. Your cam will thank you.
Have you obtained a copy of Pruitt's 'Building Cologne V6' yet?
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