Need advice for tired '87 XJ 4.0

Hi all,

Well, I've read through these great forums, and have not seen a whole lot about "pepping up" an '87 4.0 Renix motor. I totally love my Jeep (not unlike almost everyone here :spin1: ), but after being beaten on since I got it years and years ago - especially after I got my 6 1/2" lift on it WAAAY back - I kinda feel like I'm driving an asthmatic with emphysema! Where I used to be able to comfortably and easily do 75-80 on the freeway (even with my 31 x 11.50s...but have 32 x 12.50s now), now it really huffs and puffs to do 65 (and my water temp soars to over 195 when doing so...which should soon be remedied when my GDI 3-row radiator gets here, I hope)!! Pretty much, the only "performance" items in my engine bay are Splitfire plugs and wires, a K&N filter and uh.....ummm......oh geez, I think that's it! :dunno: I pulled the head off and had a valve job and clean-up done on it roughly 5k miles ago, so that's kind of taken care of for now...well, it's closer to "in good repair" than everything else, I think. One major necessity is replacing my noisy Cat, and I'm thinking of getting a Catco "high flow" universal one off of eBay, 'cause they're inexpensive and I'm unaware of any necessity in spending a whole lot more on a pricey Cat (please feel free to correct/re-direct me if I'm mistaken here).

So, I need help/advice on how best to spend $400-$600 on my tired powerplant. Mind you, this is a "for-the-moment" budget as I hope to have at least that much to throw at it in the near future. I'm just trying to determine a good starting point, I guess.

So far, here are some considerations I've been thinking of looking into further -

• Changing intake manifold to an HO (if that's a viable option), and changing the computer to a MOPAR HI-Perf one
• Just converting to an HO TB and spacer (with used parts and help from some machinist friends)
• Header (Borla? Thorley? looking for best gain/least worry of breakage for the $$)
• Upgraded injectors (possibly along with upgraded manifold or TB)
• Cam (have seen some recommendations here in the forums)

...or combinations of these (or parts of these). Any and all suggestions are definitely appreciated! I do have Dr. Dyno's very helpful page in my favorites, and have been doing some reading there (very nice, by the way, Dino!)...but I'm really looking for '87-specific kind of info and advice. I'd love to bring my beast back to life soon, and would really love to improve my 12-14 mpg!

Thanks in advance for anyone taking the time to toss me helpful advice on my geriatric Jeep! For now I'm off to go price new leaf springs for the "droopy-drawers" situation my suspension is in now...after 11 years of pre-running and 2 offroad competitions. :gee: So much to do to my poor, semi-neglected friend!

Pyro

Having an '88 Comanche, there are some place for parts. XJ-Armour is one.The main concern as far as replacing the intake manifold would be if you live in a smog state and need to keep your EGR system. You might be able to adapt a newer manifold with some work. If you plan on keeping your EGR, your selection of headers is limited or you will need to modify one. Pace Setter and I think Borla or Banks list ones for 87-90. From what I understand, the only difference between an 87-90 and newer is the EGR boss. I have heard the Clifford headers have the boss, but the header would need a hole drilled. You could get a bored out TB for the Renix. I think 58-59mm. Not as big as the HOs. You might look on E-Bay for Artsounds. I hear he does the Renix TBs. He told me he scraps about 1 in6 due to casting voids. I also hear he has a 60 or 62 mm for the Renix running as a proto type. It still has idle problems. He might be buisy with the Hurricanes in Florida at the moment. Might think about a cat-back exhuast too.
Tom

PyroZona said:

Any and all suggestions are definitely appreciated! I do have Dr. Dyno's very helpful page in my favorites, and have been doing some reading there (very nice, by the way, Dino!)...but I'm really looking for '87-specific kind of info and advice.

Click to expand...

:cheers:
Many of the mods for the HO 4.0 also apply to the Renix. A few well-chosen ones will really bring your engine back to life and it doesn't have to cost the earth either. It sounds like your cat is plugged up and costing you performance as well as making the engine run hotter, so I think you should start there. Here's what I suggest:

1. Exhaust: Carsound or Catco high-flow cat ($40 on e-bay), Dynomax Super Turbo cat-back ($95 from Summit Racing).

2. Intake: A bored Renix TB would be good but I think a bored HO TB with spacer would be better. You can adapt your Renix TPS to the HO TB. Make the hole at the front of the airbox bigger, add a larger diameter duct, and point it forwards towards the grille. Insulate the airbox Dino-style with foiled windshield sunshade to keep the air cool.

3. Strap a Thermotec insulating blanket to the underside of the intake manifold to reduce heat soak from the header underneath. For just $35, this is an excellent mod. Lower underhood temps. are another bonus.

4. Ford 19lb injectors. Plentiful and cheap on e-bay. If you still have the factory originals, now's a good time to ditch them.

5. Relocate IAT sensor to airbox (you'll need to extend the wiring but that's a piece of cake).

6. Replace the crappy clutch fan with a Zirgo electric unit (at least 14" diameter, cheap on e-bay) that you can mount to the stock fan shroud. You'll gain a couple of ponies and maybe 1mpg, the engine will rev up faster without the drag of the clutch fan, and cooling will be better.

7. When you've saved a few more pennies, you can deal with the front half of the exhaust by replacing it with a Borla header and downpipe.

8. By this time your engine will run hotter so you'll need a Robertshaw 180* t'stat from http://www.flowkooler.com (a mere $10) to cool it down again. With a cooler running engine, the knock sensor won't be working hard to retard the timing to prevent detonation so you'll gain a bit more performance.

OK, now I think I've made my prescription long enough for your elderly 4.0. If you find that you still want more performance after you've done all that (it WILL become addictive), you could always follow my lead and build a stroker in your spare time.

Um stroke it!!!!
I am running a renix stroker so I have done about everything you can do to a renix. If you don't want to swap an HO head on, you can use the HO (99+ being the best but probably the most work) intake manifold but you have to move the locating dowels. You might as well put an HO exhaust manifold on while your at it. They flow better than the renix unit and are way cheaper than a borla. You can port the head also, if you feel like pulling it off. A cam can really wake an engine up. I run a comp250h and the low end torque is awsome. If you do a cam swap you have to change lifters so the head comes off (port and polish). You can swap in an HO fuel rail and HO injectors and fuel preasure regulator. Relocate your IAT to a homebrew FIPK tube and run a cone filter. As for the MP computer they are hard to come by because they have been discontinued for a while now, but they are probably worth it.
Good luck.

WOO HOO!! Thanks guys!! I was hopin' for a little from you, Dr. Dyno, but that "prescription" of yours is GREAT! I actually already have a Catco Cat on the way...should be here today or tomorrow, I think. I also just put my new GDI 3-row radiator (from XJ Armour) in and that seems to have done a ton of good for the heat issue so far. I've also got a 4.10 ring and pinion on it's way for the rear (for now...lost the auction for the matching front set, dammit!! :lol. So, things are looking to be coming along nicely, I think.

Unbeknownst to me, luck has apparently been hangin' around me, as I ran into an old friend of mine who works at my local Dodge/Jeep service center. YAY!! So I now have an awesome source for getting an H.O. head for next to nothing. He's keepin' an eye out for everything I'm gonna need already...heh.

One thing I'm curious about, though. Everyone here seems to be raving about Borla and Banks headers, but nobody seems to be running a Clifford. When I was ordering my GDI radiator from XJ Armor, I was fortunate enough to be able to kinda pick Steve's brain about performance mods (great guy, by the way...very friendly, helpful and happy to share info), and he told me the same thing I've heard for a number of years - that Clifford is THE way to go since they've been doing R&D on I-6 engines for so long. The "scavenging" design of the Clifford header (kinda where Thorley got the idea for theirs, apparently) just makes sense. Granted, the Cliffords aren't a quick bolt-in deal (the two-piece one, anyway) like Borla or Banks, but I'm thinking the little bit of extra work may be very worth it. Anyone have any experience running a Clifford header around here that could maybe help confirm this?

Thanks for everyone's helpful responses! I'm headed to Valley Spring today to see about some new leaf packs for the saggin' rear of my soon-to-be-sweet-again ride. I'm hoping they'll live up to what I've heard about them here locally. Supposed to be quite impressive and affordable. I'll let ya know when I find out!

Pyro