'86 2.5L TBI engine mods, while I'm installing a header?

Hi all,

Finally tackling the exhaust leak on my '86 XJ w/ the 2.5L, that I suspect is a cracked manifold. I found a custom made header on CL for dirt cheap, which I'll be installing in a few days. Right now, I'm taking it apart for the install. What a complicated mess of wires and vac lines this TBI motor has.. crazy. I'm running a flexalite aluminum (loud) fan on the motor, but have a nice crown victoria police interceptor electric fan that I'm in the process of mounting, with a variable speed control unit. It's quite, and should be less of a drag on the engine. I'm also running a newer hi-flow cat and Flowmaster 50 series muffler. Once the header is in, I'll be running new 2.5" pipe to the cat.

So a few questions:

1) What else can I do while it's apart to help the performance of this motor, if anything? I know the multi-port injection 2.5s make more power,and I've seen these intake manifolds for sale, but I'm not sure if that's a feasible, or even possible swap. Probably more than I want to tackle, if it involves wiring harness, ecu, fuel pump changes etc..

2) My intake manifold has coolant lines running through it, apparently to help vaporize the fuel mixture? This seems to defeat the purpose of running a cold air intake it would seem.

3) So as far as air intake, i've been running a K&N filter straight off of the top of the TB. I plan to route the intake air to the firewall on the pass side, below the windshield wipers. This should get me colder air, which I hope will help.


This poor thing is turning 37" Maxxis Creepies with 6:50 gears, and any performance gain would help, ya know.

Thanks,
Cameron

Pretend like I wasn't here

me thinks his 2.5L is gonna be a little different than the 2.8L swap

I have the 2.5L, not the 2.8L... This swap is still doable?

BTW, I learned to drive in my parent's 2.8L 5-speed XJ... what a turd. I like my 2.5 better than that thing.

Cameron

You could swap MPFI off an early 90s 4cyl without much trouble. IIRC you'd need the intake manifold, throttle body, sensors, flexplate or flywheel, wiring harness (you'll need to customize it / splice it with your stock harness), and ECU. Maybe fuel pump as well.

I'm not too familiar with the 4cyls though, so take this with a grain of salt.

Kastein,

Why the flexplate or flywheel? Not sure what that would have to do with it. Internal vs. external balancing?

I imagine that the fuel pump psi output would be higher with the MPFI, but that may be one of the easier swaps. Having never dealt with wiring harnesses and engine swaps, I'm pretty much new to that arena.

On the RENIX TBI 2.5s the flexplate/flywheel has a different pattern of notches on the edge for the CPS to read than the OBD-I/II MPFI 2.5s has. Otherwise, you could just bolt on the appropriate sensor for the year of ECU you use and it'd work.

Not sure how much extra power you'll get from MPFI vs TBI - I'm sure it's documented somewhere.

You should be able to get rid of the coolant running through the intake easily enough - just bypass it. Not sure why they did that, anyone have ideas? My guess was to give the older carbed 2.5s more stable intake air temp to work with but I could be completely wrong.

Yeah, I
I've thought of bypassing the coolant lines for a long time, but was unsure of possible detrimental effects. I'll give it a shot when I get her back up and running. One thing I've noticed with this rig is that when it's cold in cold weather, it'll die once started, unless you keep on the gas for maybe 30 seconds...

I forget the figures, but the MPFI engines gross a considerable amount of hp/torque over the tbi models.

CameronB said:

.I forget the figures, but the MPFI engines gross a considerable amount of hp/torque over the tbi models.

Click to expand...

105 @ 5000rpm carb
130 @ 5250rpm MPI

neither number is very good, but the additional 25hp is definitely noticeable

Hmmm, a 4.0L swap is starting to sound better to me... but I do enjoy the lighter weight and engine compartment room I currently have.

Too bad there's not an affordable turbo or supercharger system available for this little motor...

Can you believe that my exhaust leak was bc there was NO GASKET!!! Can't believe that... and can't believe that it took so long to noticeably leak.
There was only an intake manifold gasket. Who knows...

So, this header from a Wrangler that I'm trying to fit is being a turd. There are 4 long runners into the collector directly in front of the low portion of the oil pan, which I'll probably have to drop in order to mount this thing. Hope it fits.

Not sure yet if I can bypass the coolant line that runs through the intake manifold, bc there is a bung with my CTS there. We'll see.

As for performance, I spoke with Larry at Clifford Performance, who has an intake for 400, Weber 38 dgev for 500, short duration/high lift cam 300 iirc, high flow chevy valves, and recommended decking the block to attain 10:1 compression. Said that this set up should reach 220+ horse, 325 ft/lbs. That's about 1800 bucks though, which I just don't have right now.

What do you guys think?

That's a pretty damn nice torque number for a 2.5 - what I would do though is look into a tbi swap using megasquirt and a chevy throttle body, instead of spending 500 on a carb. I suspect you can do it with a combo of junkyard and rockauto parts for under 300, though I don't recall what prebuilt megasquirt costs. The rest sounds pretty good imo.

I wheeled a 85 2.5L carbed, ten converte it over to throttle body. It made a huge difference. I can't believe that you would gain that much more by going mpi. I added a Mopar Purple Cam. For wheeling the biggest help was an 11lb flywheel weight.

Tom,

Who makes the 11 lb weight that you used, and what was the overall effect it had? Did you convert it to factory TBI?

For that price, or less, you could swap in a SBC.. mmm... power.
Novak and AA both make adapter mounts.

There arent many places that still have 2.5 performance parts left. MOPAR no longer carries cams for them, and the only other place Ive found that does is 505 Performance, they also have a turbo kit, and a stroker kit for it, but as was said, all this stuff is pricey. But for someone who wants to keep the 2.5 these are some good options.

http://www.505performance.com/

As far as your intake manifold, Ive heard tell of a restrictor in the stock 2.5 intake that is somehow removable, though Ive yet to remove my own intake to confirm this. Ive also done the cold air intake, the electric fan, gutted and sleeved the cat, and installed a Flowmaster 50 series. These all gave me minor gains. There are also higher ratio rockers available for the 4.0, and I beleive these will fit the 2.5. And heres a link to another thread on bumping up the diplacement. Theres no confirmation in this link as to if this really works, which bothers me a little, but I have a spare motor sitting ready to try some stuff out on.

http://www.jeepforum.com/forum/f12/2-7l-amc-4-cylinder-take-look-457885/

Boy,
This header was not made for an '86 xj! First I had to heat and bend them to clear my rear sump oil pan, then grind on the bottom of my intake manifold... and now the ps pump bracket has a 3" section cut out to clear the front runner. Going to have to get pretty creative now!

I'd post some pics from my phone but don't know how. I'll keep ya posted.

CameronB said:

Tom,

Who makes the 11 lb weight that you used, and what was the overall effect it had? Did you convert it to factory TBI?

Click to expand...

Tri-county gear in California made the one I had. Yes, I updated to the full factory wiring harness/ecu for the 86 IIRC. I ran the Clifford header.

It worked great for wheeling but just didn't have the balls to pull the mountain passes at the speed limit here in Colorado.

You can still get the Mopar Purple Cam

http://www.chicagoconnection.us/index.php?main_page=product_info&cPath=1_377_379&products_id=1777

Thanks Tom.
How do I post pics?

Exhaust is DONE!!! What a pita... It's a 3-bolt collector flange of 2.5", mandrel bent 90* back, then reducing to 2.25" all the way to the muffler, and 2" to the tail pipe.

Ended up modifying brackets, lot's of grinding, and fabbed up my own exhaust to a Flowmaster 50 series, no cat. My O2 sensor fell apart, so I'm ordering one now.

Question:
Looking on RockAuto, there are only three sensors that clearly show three wires, like my stock set-up (heated sensor.)
One is 'NTK' = $21.79
One is 'Standard Motor Products' = $31.79
One is 'Delphi' = $37.89

What do you recommend?
She still just barely runs when cold, unless you're on the gas. Hoping the 02 sensor is the only problem

Oh, and the Police Interceptor Fan is tits :eeks1: