2.5L performance?


The outside diameter of both TB is the same. Intake parts are therefore intercheangeable. My 2.5L has a 4.0L snorkel and fits just fine.
 
I replaced my stock 2.5 TB with a cherokee 4.0TB, great breather mod. Noticable throttle response. BTY, I heard that the sensors and everything are the same on the two throttle bodies, its just the intake size on the 4.0 is slightly bigger. Also, remove the inner cone-shapped restrictor ring and plastic plate inside the air box if stock, that adds air too.
 

Had posted a posting about not sure about keeping the 2.5L but with all this info I believe Im going to leave the engine and modify it.
thanks for all the info
 
The 2.5L is a good little motor. It is based off the 4.0L with the same bore and stroke. Just 2 less cylinders. Only time I missed having a 4.0L in my wrangler was on the freeway. I'd take a 2.5L over a carb'd 4.2L any day. Both the 2.5L and 4.0L are good motors either way.
 
TwistedCopper said:
While I'll agree that no single mod will have a huge impact for a 2.5L, doing several can. The most bang for the buck is a electric fan conversion. Instead of trying to squeeze more power from the motor, it frees up some that were already there but being used ;)
Click to expand...

I agree; personally, I have a ton of mods on my little 4-popper, and the difference IS felt. I currently run the following:
  • Snorkel (CAI and Ram effect)
  • High flow filter (stock box)
  • 62mm TB with 62mm TB spacer
  • 46PSI FPR
  • Mopar Performance Camshaft
  • 19# Bosch Mustang injectors
  • PD ignition with plugs gapped at .060
  • High Flow Cat
  • Borla Cat Back
  • Ford eFan with DC Controller
  • Aluminum rad (cools faster, making the fan work less)
  • 4.10 gears
  • Roller rockers (reduce friction)
  • Synthetic oil (again, less friction)
Biggest differences noticed have been (1) regear, (2) fan, (3) TB, then the rest; it kind of has to work together. No sense in allowing for a ton of air if there is no capacity to adjust to the required fuel amount. Same happens if you get a ton of air, the right amount of fuel, but the ignition is weak or the exhaust limits the next stroke.

On the trails, I have no problems keeping up with the 4.0L wranglers out there. On the road, it drives just fine. On the highway, the wind resistance does get to it when you get past 60mph (if there is a headwind, you need to downshift to 4th). I think for my setup, 5.13 gears would be perfect, and then I would be able to keep with any 4.0L I have wheeled with, but that means 2 new axles, so it's not happening.

The reason I think 5.13 isperfect for 33's is that although all the charts say 4.10 is the right gear, putting it back to stock form, they consider only torque, but not wind resistance caused by the lift and bigger tires, as well as rolling resistance from the tires themself.
 

northshore29 said:
have any of you tried those performance chips that trick your pcm to think the air temp is colder than it really is? i imagine it would just ruin your gas mileage dumping that extra fuel, but w/ a 4.0L throttle body, ram air intake, and maybe a header i'm thinking i could get an extra 15-25hp. if anyone has a wild hair and extra $600-$700 to try it let me know how it goes.
Click to expand...

Go to Radio Shack and buy the 22k ohm resistors. Hook 2 in line. Add them to the signal wire of the IAT sensor. (Black and Red wire). What this does is trick the pcm into thinking it is 16 degrees outside. I did it to a 4.0 and a 2.5. My 2.5 actually feels like it has some pull now. As far as gas mileage it went up a little because I am not in the throttle all the time.
So you spend a dollar for 5 resistors (enough to do 2 vehicles). You were thinking $600 for an improvement like that . I just saved you $599, buy me a beer someday.
You can also mess with the coolant temp sender. Just be careful because too much resistance will set off the Check Engine Light and start causing driveablity issues. I wouldn't recommend unless you are good with electrical. The IAT is easy. The CTS will have adverse affects if you calculate resistance wrong.
Good Luck
 
warpedredneck said:
isnt the 2.5 a general motors motor?
i was under the impression that the 2.5 is what they called the iron duke motor. it this is the case there is a lot of stuff available for this engine! cams, pistons, roller rockers even performance heads.
can some one tell me if i'm right or wrong?
thanks
jeff
Click to expand...

90growler said:
It's an AMC Design with lots of GM parts to my knowledge.
Click to expand...

The Iron duke was a 2.5 cross flow head designed GM motor. Intake and exhaust manifold are on opposite sides of head. Last Jeep to use is was a 1986 Jeep CJ 2.5L. Jeep Comanche, Cherokee, and Wrangler all used the AMC designed motor, 2 completely different motors. AMC / Jeep 2.5L and 4.0L motors share alot of same internals, pistons, bore, and stroke. Similar motors. I had a 1991 2.5L crank bearings went out. Had it boared and stroked. Actually helped some in bottom line and TQ. Engine shop said at the time, Cam and crank were a PITA to find, but that was in 1999. They might be easier to get nowadays.
 
just a shout out for the 4 banger. I started my love with a 90 yj 4 banger, daily driver for 7 yrs. It went everywhere, it handled trails and sand better then my later bought I6 92 yj. To help my 4banger get to the trails i installed a F-250 SD infront of it.
 
Like I said before check this wicked power spacer, it works wonders, I believe it is gsppowerspacers.com
 
Last edited:

O yeah on my lil 4 banger along with all my other mods, I am going to try to relocate the IAT sensor (Intake air Temp) . I will keep my stock one in place and purchase another and extend the wires so I can place the sensor inside my air filter intake box. This will then pickup ambeint colder outside air instead of hot air from inside the intake manifold. The colder air to sensor will enrich the air fuel mixture and will slightly advance the ignition timing as lower temp signals are sent to the ECU. The results should be faster throttle response and a slight increase in horse power only at (WOT) wide open throttle. I have done the researh on this and there is no downside. No lose in gas mileage, and you can always plug back to factory sensor, sense it is still in place. We will let you know the outcome. This way there is no chip and no fooling the sensor, it will physically and truly be picking up colder air. Little 4 bangers a known to run on the lean side anyway. Adding better spark also helps such as accel coil, 8mm wires and I also run NGK plugs gappped at .037. Happy 4 wheeling, my fellow jeepers.
 
O guess what I did the other day, sense i can not afford a electric fan right now and also been debating between electric or flex. I took a pair of tin snips and little by little cut down my factory fan. Very carefully sniped of the corners of each blade, about half inch measured both ways from corner. This is the corner closest to engine. Then I got brave and took a wide pair of pliers and slightly bent about quarter inch at corners to further reduce air drag as the fan rotates counter clockwise. The bend was slight, a hair less than a 45 degrees. To my surprise the little 4 banger seem to wind up alot easier and faster of the line and down the freeway, with less effort. My concern was I thought my temp gauge to going to run hotter, but it was running cooler. I am going to hold of on any electric or flex fan for now. Runs so easy and smoother I just might keep it the way it is. Ok sometimes I talk to much gotta go. My jeep has four angry squirrels under the hood, feels good. Catch you later fellow jeepers.
 
quicksand97 said:
O guess what I did the other day, sense i can not afford a electric fan right now and also been debating between electric or flex. I took a pair of tin snips and little by little cut down my factory fan. Very carefully sniped of the corners of each blade, about half inch measured both ways from corner. This is the corner closest to engine. Then I got brave and took a wide pair of pliers and slightly bent about quarter inch at corners to further reduce air drag as the fan rotates counter clockwise. The bend was slight, a hair less than a 45 degrees. To my surprise the little 4 banger seem to wind up alot easier and faster of the line and down the freeway, with less effort. My concern was I thought my temp gauge to going to run hotter, but it was running cooler. I am going to hold of on any electric or flex fan for now. Runs so easy and smoother I just might keep it the way it is. Ok sometimes I talk to much gotta go. My jeep has four angry squirrels under the hood, feels good. Catch you later fellow jeepers.
Click to expand...

I am not sure I would have gone this route for a couple of reasons:

1. When wheeling (ie. 4L and crawling over obstacles), the Jeep tends to run a lot hotter than ussual, so the fan has to work extra to keep it cool. Clipping 1" around will (1) hurt the fans ability to cool the engine because of less pulling power, and (2) make the fit with the shroud loose, causing even less air to go through the rad
2. The e-fan option is actually quite cheap if you do it the junkyard way... I paid $28 for my fan and shroud from a mid 90's Taurus, and it came with the shroud which almost (except for one bolt) was an exact fit for my rad. Ad a 30A relay (the slow speed is more than capable of cooling the Jeep), a switch and some cables, and I doubt it will get to $50, and that can hold you until you can afford a controller.
3. It is quite easy to unbalance the fan by cutting the blades. You may not notice it, but the vibrations can cause havoc down the line...

Felipe
 

I'd be worried about the fan becoming out of balance, shortening the life of the water pump.
 
Question for JFRABAT, actually my jeep for some reason cools down alot faster with that factory fan trimmed down a bit, even in traffic on a hot day the gauge does not even hit the mid point. My question is did you gain any ponys from electric fan?, and what is your take on a flex fan?. My latest mod is I bored out my intake manifold just a little more, I believe its bored out to 56mm, does not sound like much but it matches my power spacer from gsppowerspacers which has a bottom bore of 55mm and top bore of 60mm. This keeps the incoming air under pressure. More air is good but you lose air pressure you lose torque and power. My TB is also tapered Top-60mm, bottom 55mm. I went bigger before and lost torque. The 4 banger is very sensitive. I believe it is like a funnel or like water pressure affect, it starts bigger and is pressured to a smaller opening. I do have a accel coil and 8mm wires with NGK plugs gapped at .37. I am going to test running a bigger gap. Remember 4 bangers usaully run on the rich side. Need to burn that fuel. Thanks Later
 
OK, let me start by saying I have not dyno'd my Jeep, so everything I say is not backed up by data (it is from a theoretical point only).

Regarding the fan, in theory, switching from mechanical to electrical should result in some loss, so when the fan is actually on, it is less efficient than the mechanical fan when it's on. The good thing about the eFan is that (with the right controller), it will be off when it is not needed (say, when you are driving 30mph or faster). Also, the speed of the fan is independent fromt the speed of the engine, which means if you are rockcrawling in 4L, you can turn the fan on a full speed and it will cool a lot faster than the mechanical fan.

Now, to say I have noticed a drastic change when switching from mechanical to eFan would be a load of crap. Does it help? Yes. Is it a night and day difference? NO. Would I do it again? Yes. Does it free up some ponies? Yup. Will you feel them with the but-dyno? Probably not, but you will be less likely to shift down to 4th on the freeway. In my case, I did a prior run to see where I needed to downshift on an overpass in Miami, and with the eFan, I would not have to shift until higher on the ramp. Later, with the 62mm TB, I did not need to downshift at all... Of course, the test is not 100% scientific because it does not factor in the wind speed or the fuel weight (fuel tank at different fill levels), so keep that in mind.

As for the Flex-A-Lite, I have no gripe with them other than why pay $100+ when you can get something just as good for $30 (ford fan).

Now, regarding the TB, what you really want is no restrictions at all. This means as straight as possible piping from the filter to the TB with no restrictions (ie. the diameter is always constant). Now, the intake manifold can be opened to 62mm (I think even 63mm is still doable), and the 4.0L TB can be bored out to the same. TBS you can make your own or bore the one you have out to take maximum advantage. By the way, if it has that spiral thingy, that does nothing to help your HP... You want a SMOOTH surface...

As for the air pressure, I would not worry too much about that; in my opinion, the formula is simple: you need air, fuel and spark. For more power, you need more fuel. To burn more fuel, you need more air. The ECU will compensate, so more air and more fuel will give you more power at WOT only (something to keep in mind). By the way, I run a little higher pressure than most (46PSI) to compensate for the 62mm TB, cam and other doodads that I have on my rig...

As for the plugs, I have run the accel coil and the Screaming Demon ones; I have gapped my plugs at .060", and it still runs nicely, but I have also fried my coil, so I am now considering to lower the gap a bit (especially since I got a 600 mile road trip coming up; last time I made the trip, I ended up having to swap coils in the middle of nowhere at night under the rain! NOT FUN!).
 
You must log in or register to reply here.

Similar threads

L
Low Oil Pressure
Replies
3
Views
5K
superj
superj
Skulljeep683
2.5L performance - hate it or love it, don't care.
Replies
12
Views
38K
Skulljeep683
Skulljeep683
L
I thought the same as many of you. This EconoAid throttle body spacer must be a joke
Replies
4
Views
34K
camshaft38
C
69jeepcj
Vacumn advance
Replies
2
Views
3K
69jeepcj
69jeepcj
B
Engine and Suspension Performance
Replies
6
Views
3K
hoobness
hoobness
Back
Top