Topic: 2.5's power curve?

[shotgun]

I would really be interest in knowing if anyone has made a tbi to mpfi swap and what they ran into.  I lucked upon a 95 engine, tranny, transfer case and computer for next to nothing. I was not able to get the wiring harness.

So I know I'll need the engine compartment wiring harness, fuel pump and exhaust  mods. Is there anything else?  I heard the gauges run the same voltages but what about the in dash harness? One guy said just unplug from one firewall and plug in the other.

[Jeffy]

Holy John Crapper.  Something's got to be wrong in my jeep or your driving on flat ground to downhill all the time.

the only time I see 70 is going downhill with a tail wind pushing. I normally run 4th at 3000Rpms and see 55-60mph. going up a regular hill  this is all I can maintain. anything relatively steep or with a posted grade will drop me to 3rd in a heart beat.  Anything over 3300 RPM and I can't feel any power in the jeep.

mind you this is an 87 4banger with 4.88s and narrow 35's ( 34x10.50 ltb to be exact.

I suspect quite a bit of blow by, but not noticable oil burning. but I think crankcase pressure is blowing oil out the dipstick as after long high rpm runs (1hr 20min.) the side of the engine is covered with oil and the stick drops about a quart. Replaced everything but the head and manifold gaskets and can't find the leak. Doesn't leak a drop just going around town.

34x10.5R15's are narrow but heavy tires because they are bias ply.

The TBI's are down on HP by about 12.  Blow-by means your engine is not efficant anymore either.

[Jeffy]

I would really be interest in knowing if anyone has made a tbi to mpfi swap and what they ran into.  I lucked upon a 95 engine, tranny, transfer case and computer for next to nothing. I was not able to get the wiring harness.

So I know I'll need the engine compartment wiring harness, fuel pump and exhaust  mods. Is there anything else?  I heard the gauges run the same voltages but what about the in dash harness? One guy said just unplug from one firewall and plug in the other.

You'll need the gas tank, tank skidplate, fuel pump and sender.  You'll want to get the exhaust down-pipe.  You will probably want to double check the evap cansiter to see if they're the same also.  The gauges are different between the pre-90 and post-90 YJ's.  There is no clock so they are in different positions.  You'll probably want the speed sensor from the T-case, too.  I'd get a late model FSM and compare it to a pre-90 to make sure you won't have to change the pin-outs.

[sbspence]

http://us.f1.yahoofs.com/groups/g_2188115/2.5+Dyno+chart/__hr_2.5+Dyno+Page+1.gif?bcT_OFDBxnhEMY2d

http://us.f1.yahoofs.com/groups/g_2188115/2.5+Dyno+chart/__hr_2.5+Dyno+chart+(Page+2).gif?bcT_OFDBLlW.RTFs


 (((SHRUGS)))  Cut/copy/pasties I guess...

[Sparky Watts]

Sorry for dredging up an older topic, but thought I'd throw in my 2 cents from the flatlands.....

If I'm just cruising to work on the back roads at 55-60, I can run 5th gear at about 2200 RPM and am currently getting between 23 and 25 mpg, depending on how I drive it.  I generally shift around 2500-2700, unless I'm trying to merge into traffic or late to work, then I can run up to the 4500 range and get all kinds of gitty-up boogey power!  I've done mileage tests at different shift RPM's, and the 2500-2700 range is generally the most fuel efficient, and it drops off pretty quickly to sub-20 mpg if I run my shifts much higher than 3500.  I've got the stock gears and 31x10.50 mudders, and can pull up gentle inclines at 60 with no problem in 5th gear.  When I get back into eastern Kansas where my property is, the hills are much steeper (much like Arkansas or parts of Missouri), and I have to pull 4th to make the grade.  I can run 70-75 mph in 5th on the flats around here (Wichita area) as long as the headwinds stay below 15-20 mph, then I have to go to 4th.  This is all with speed compensated by the proper speedo gear swap after the larger tires, and double checked with GPS.  

I have found out since I put in the electric fan and pulled the air restrictor tube that if I try to run 2nd gear up to 4000 RPM's on wet pavement, it gets all kind of squirrely, and will kick sideways when I slap it into 3rd on a speed shift!!  Sure put a spot in the seat when I found that one out!!

[Jeep_Lust]

The spec sheet that I pull up for the Wrangler 2.5 (Cherokee was tuned higher) shows TBI has 117 hp & 135 ft. Lbs.; MPFI has 121 hp & 139 ft. lbs. of torque. The MPFI makes peak torque @ 3250 rpm, compared to 3500 rpm for the TBI.

With a '90 TBI, I cruise in 5th @ 65 mph @ ~2700 rpm. This is with 29" (235-75) tires & stock 4.10 gears. This checks out with the gearing calculator as well.

It's my understanding from reading other posts and other sites that you need the dash harness, fuel pump & speed sensor, as well as the engine harness (of course), the ECU, and the downpipe.

I'm collecting all of these bits, as I have a '94 engine that has MPFI; but I'm not sure that it's worth the hassle to do the swap for 4 hp & ft. lbs. until I do a complete frame-up overhaul.

[dexetr30]

I've said it before... and I'll say it again.

Holy old thread revival Batman!!!!!

[jfrabat]

JP Magazine had the Dyno results of a stock 2.5L (with some miles on it) compared to the same rig with some upgrades (4.0L TB, CAI, headers, high-flow cat, cat back, and ignition if I remember correctly...).  I'll try to scan it and post the picture today... 

According to that chart, the torque for the 2.5L started to pull at around 2,300 RPM, and increased to about 3,300 if I remember the chart correctly, but I will check today.

Felipe

[Chad]

I have a 99 TJ with a few upgrades such as 4.0 TB and spacer, running some bald 31x10.50s and i have seen results much like shotguns.  Trouble getting up past 65 can't go 70 or 80 no matter what. My gas mileage is crap too around 15 in the winter months

[jfrabat]

JP Magazine had the Dyno results of a stock 2.5L (with some miles on it) compared to the same rig with some upgrades (4.0L TB, CAI, headers, high-flow cat, cat back, and ignition if I remember correctly...).  I'll try to scan it and post the picture today... 

According to that chart, the torque for the 2.5L started to pull at around 2,300 RPM, and increased to about 3,300 if I remember the chart correctly, but I will check today.

Felipe

Here's the article...



Felipe

[dunklervogel]

That is somewhat discouraging... but then again I bet the main reason for the loss of low end power was from the exhaust.

[jfrabat]

That is somewhat discouraging... but then again I bet the main reason for the loss of low end power was from the exhaust.

Actually, I read somewhere (dont remember where, but it could have been JP Magazine as well!) that the headers reduce low-end torque (they gain power at higher RPMs, though).  Dont know if that is tru or not, but I can tell you I dont plan to change my headers until the ones I have die on me...

[chrisfranklin]

That's a good JP page to see.  Fills in the blanks on a few mods you might or might not entertain doing.  Other than maybe re-gearing, I am personally done with messing w/the performance on mine.

[jfrabat]

I superimposed the data from the before and after and added a difference between the two (difference is on the second axis, so look right for the values of this one) so that it is easier to read...  I had to estimate the values from the chart, but it should be close enough.



My guess is that most of the improvement came from the CAI, but I dont know...  But to be honest, a 10% increase in torque (at the wheels) is not a bad gain at all!!!

Other than maybe re-gearing, I am personally done with messing w/the performance on mine.

I do plan to regear and add a couple more mods, but only one or 2 of these will be directed at increasing power (one of them being new 4.88 gears for the 33" I intend to run); most are intendend to increasing traction and adding protection (like lockers, winch, snorkel, etc.).

Felipe

[dexetr30]

As for the header... I don't think that I would remove the stock manifold. Seems like you lose a lot on the bottom. That's not something I have an interest in. I'll be installing my e-fan as soon as it gets a bit warmer up here. The 4.0l throttle body was a great addition to my 2.5 and I won't go without it now. I may add t.b. spacer soon but it seems as though people have had problems with them in conjunction with the auto trans. C.A.I... I won't bother. I swapped my cheesy home built intake for a 4.0l intake tube and box. It looks a bit messed up the way I had to put it together but it works nicely.

It's pretty interesting actually seeing a dyno chart for some of the most popular mods for the 4 banger. 14% is nothing to sneeze at with these engines. It's just to bad it lost so much on the bottom.