Yesterday a 4.0L TB from a '98 Cherokee arrived by UPS – to be installed on a 2000 2.5L TJ. With the help of a neighbor who teaches auto mechanics at the local high school (absolutely cool woman who decided to make it a day project for some of her students), I dyno-ed everything in stages. Checked the air flow, too.
Results, with stock (2.5L TB & no spacer)as baseline:
(1) Poweraid spacer only – +2 HP, 8% less airflow (Evidently, the helix bore, lips of which extends beyond intake & TB opening, actually cuts down on airflow. But the spacer does “cool” and extend air volume, hence horsepower increase.)
(2) 4.0L TB only – + 6 HP, 16% more airflow (no surprise here)
(3) 4.0L TB & grind out intake opening to match lower TB opening – + 13 HP, 29% more airflow (Wow! Grinding out the intake opening did make a difference!)
(4) 4.0L TB & Poweraid helix spacer & grinded-out intake opening – +16 HP, 2% less airflow from #3 above(overlapping helix bore is still cutting off airflow, but spacer is still cooling & increasing air volume)
(5) 4.0L TB & grind out helix bore in Poweraid spacer to match lower TB opening & grinded-out intake opening (the Big Kahuna) – + 24 HP, 39% more airflow (Wow again; the optimal configuration, obviously)
It should be noted that grinding out the helix in the Poweraid spacer still leaves a partial helix in the walls – the main difference being that the helix now has rounded edges rather than sharp ones. My auto mechanics-teacher neighbor suggests that these rounded edges are actually more aerodynamic than the original sharp ones, and will still “spin air” – so perhaps the “pulse-organizing” effect I mentioned in an earlier post will be retained, if in fact there is such an effect.
So, to reiterate, I ground out on the helix bore of the Poweraid spacer, and ground out the intake opening, both to match the lower opening of the 4.0L TB I swapped in. Dyno-ed & tested airflow, results: +24 HP, 39% more airflow.
Seat-of-the-pants impression: idles smoothly, more torque on the low end, smoother accleration through the midrange, and better performance above 2700 RPM. No hesitation, no engine codes.
One MAJOR suggestion: if you grind out your intake opening, be VERY CAREFUL about aluminum filings in the intake manifold. We stuffed everything with tack cloth – sticky cloths which can be purchased at a hardware store – rather than shop towels. The tack cloth caught about 95% of the filings, but there was still a small mess in the intake. We vacuumed a lot of the leftover out with a shopvac, but we still had to use tack cloth attached to a long, thin screwdriver to “mop out” the runners. On the TJ there are also four open plugs/hoses attaching to the intake below the TB – you'll have to clean those, too. It took longer to clean out the intake than it did to bore out the opening, but it can and needs to be done.
Finally, should say that the TJ has a two-stage K&N filter system, an MSD ignition system & coil, high-gapped Champion truck plugs, a Flowmaster delta-40 catback, and a case-full of Mobil 1 synthetic oil. All or part of which may have a synergistic effect on my results, since mods usually affect each other.
More Info: (1) The intake is soft aluminum, so we used a medium tungsten rasp, followed by a fine fluted grinder bit, followed by a fine polisher. I'll admit it's not even – hard to get consistency around the runner walls which are nearly flush to the intake opening. The spacer is a harder grade of metal, and trickier, even when clamped in a vise. Doesn't look pretty anymore, at least on the inside.
(2) Tested at 1800 RPM and 2800 RPM with an average between the two – but the results were fairly similar.
(3) We figured the following: At 2800 RPM, torque was up by about 16% with #5 option above. At 1800 RPM, torque was up by about 14%.
Again, folks, consider the mods and the synergistic effects – your numbers may be different depending on what you have your rig, mileage, mechanical conditions, altitude, etc. I give this just as a general indication.
Ambient air temperature: 74 degrees Humidity: about 35%
Anyone think to measure the opening on the 2.5L intake manifold BELOW the TB? If you do, you'll see it's exactly the same diameter as the 2.5L TB. If you want to see what I mean, and you don't want to take off your TB, take a look at “Jeffy's” photograph in his how-to article on this site. The photo looking straight down through the Poweraid spacer and the intake opening is the one I mean. You can see the lip of the intake opening as a silver half-curve inside and below the spacer.
You can verify this easily with calipers.
For a 4.0L TB to have ANY real effect whatsoever on the TJ, you'll have to take off the intake and bore out the opening. Whatever improvement you've been “feeling” is either in your head, or a result of the PCM reacting to modified input from various sensors. The TJ won't run “better,” but it may run “different.” If you like that, OK, do it, but there will be effects on mechanical components, and we have no way of knowing what they will be. We can only guess.
Which is what “Gear Poet” was talking about, wasn't he?
Another point: the stock TB's are designed to work in tandem with the intake manifold. The air charge is directed down into the manifold and “splashes” on the surfaces at the bottom before “bouncing” into the injector channels. That “splash” and “bounce” effect is important, and it's subject to the architecture of the TB. Changing the TB changes the effect, and likely will produce turbulence in the intake. Which means your injectors won't be laying through a properly atomized fuel-air charge into the cylinders. Changing your injectors may do some good, but without testing, who knows?
Bottom line: too much trouble, too many uncertainties. The spacer's a good idea, mostly because the air cools somewhat inside for a denser charge, and the velocity of the flow-through picks up a bit. That and the computer is where people may be seeing the change they talk about.
I'm sorry, I need to disagree with the DC Engineer…I think he's looking at the wrong thing. The opening on the intake manifold for the 4.0 and the 2.5 is the same size. But is larger than the opening on either the 4.0 or the 2.5 TB. Now compare the minimum diameter of the 2.5L & 4.0L TBI opening. There is a BIG difference.
Now he may have a point, in that, the engine is only going demand so much air. If I remember correctly from fluid dynamics.. Sucking a given volume of fluid through a comparativly smaller diameter vessel in a specific amount of time will: - reduce the pressure (increase the vaccum pressure) within the vessel. - increase the speed which the fluid is traveling through the vessel - lower the temp of the fluid.
The speed MAY help to mix the air/fuel. The lower temp the air is, more dense it is. The more dense the air, the more O2 you have avaiable to support combustion.
If you assume that the stock 2.5L is air starved we're doing the right thing. I made the convertion. All I can say is, going up and down the NH hills, I don't have to shift quite as often.
I just put a 4.0L TB on my 2.5L TJ last week. I'll verify what Gear Poet and his friend say. The intake bore on my unit is the same size as the 2.5L TB, and a bit smaller than the 4.0L TB. And I verified it by measuring a 4.0L intake bore in my neighbor's Cherokee, so I'm satisfied.
That having been said, my TJ now runs better at high RPMs, and I have to downshift from 5th to 4th and 4th to 3rd less. I've noticed no difference at at low RPMs or at idle. That's exactly what I expected, since the engine sucks more air at high RPMs. Pretty basic.
Is it worth it? Sure, for highway cruising and on-road hard acceleration. Doesn't make a bit difference off-road, though. And it won't make much difference if you drive for economy and try to be easy on your unit. It's a modification for people with a heavy right foot. But it's nice to know it's there, if you need it.
On air flow, velocity, dense air-fuel charges, and the the best sort of air induction system to have, I'm pretty much in agreement with Gear Poet and his friend again. Here's my take:
1. Jeeps do three things, one more than most vehicles. They go fast on highways, fast and slow on in-town roadways, and real slow off-road. So you're really talking about more than one solution, OK? 2. If you go fast at high RPMs, what you need is a cowl-induction system. An air-ramscoop on the hood forcing cold air down a smooth, straight, insulated tube into the intake. The tube should be of a mild conical shape to sustain higher velocities and pressures. You'll get overpressure on the scoop side, vacuum on the intake side, and a dense air charge that will practically force its way into the cylinders. Your horses will be good ones. 3. If you go real slow at low RPMs, you need a big volume of calm air, the less turbulence, the better. The trick here is to encourage consistent metering of air and fuel through the injectors and sustainable conditions through the TB and the intake. Turbulence is the worst possible condition, because at high RPMs you can momentum yourself through the “bumps and swirls”, but you'll really feel them at 1600 RPM climbing a 50 degree rock face. They can shut you down. The solution here is a big plastic box with rounded corners and an open tube going through the middle, just like the one that sits on top of the stock TJ.
(I'm not defending Jeep engineers. The box is a good idea, but where in hell did they get the idea for that upturned horn at the end, the one with an inch-and-a-half opening? I took that thing off in the dealer's parking lot.)
4. So what's the real solution to many different things a Jeep does? You've probably already guessed it. A cowl induction system at the front corner of the hood (passenger or driver side, depending on if its a TJ or YJ), and an insulated tube, straight and smooth as possible, to an insulated airbox above the TB. Inside the airbox is an open tube passing through dead air. No sharp corners anywhere.
Where to put the filter? The best place is right behind the cowl and before the tube. Then design the tube to “straighten out” the turbulence, maybe baffle it a bit.
Fly on the Wall
After reading the article on the 2.5L to 4.0L throttle body swap, I noticed one detail that was not even mentioned, changing the A.I.S motor and housing to the new throttle body.
First, let me say hello to the group. I am a tech for Jeep and Chrysler, electrical and drivability are my areas of expertise. Now I'm going to add my .02
1. I have done this mod on my own 92 wrangler with a 2.5L engine with incredible results. The 2.5L has a K&N stock replacement air filter w/ a stock air box… the restrictor in the air box cover removed, a tri-y design header (manufacturer unknown, was given to me), stock exhaust minus the cat, an Accel super coil (direct OEM replacement) w/ Belden spiral core wires and factory plugs gapped at .035”. I have 4.10 gears w/ 35×12.50 General MT's and I can say this motor screams. The motor in stock form would not pull the jeep w/ 33” tires. I did all the mods except the throttle body and put the 35's on. At 65 mph into a 15mph headwind, I would have the throttle pushed to the floor just to maintain speed in 4th gear, with the throttle body swap, it was like putting a 4.0L under the hood. Under the same conditions,I could maintain speed w/ 1/4 to 1/3 throttle opening, and my DRB III confirmed it. It felt like I added 15 to 20 hp., bottom end torque improved and overall drivability improved. Fuel milage remained constant, or slightly better depending on how heavy my foot was.
2. Now on to the AIS motor. If you look at the AIS motor and housings on th 2.5 and 4.0L engines, you will notice tha the idle air passage seat where the AIS needle seats is considerbly smaller on the 2.5L than the 4.0L, so is the needle on the AIS motor itself. You must transfer the AIS motor and housing from the 2.5L throttle body to the 4.0L throttle body, if you don't and you use the 4.0L housing and motor, you may not get your idle speed down to where it should be. Your AIS motor will be fully closed or close to it (0 to 2 steps). On TJ's this can be a problem with the OBD II, since it can trgger a code in the PCM (target idle not reached), so be sure to transfer it to the 4.0L throttle body. Be careful with the gasket it is not available separately. If done right and you have access to a DRB II or DRB III or a code scanner your idle steps should be around 14 to 18 steps in neutral, air off, if not you can fine tune to get it in that range by adjusting the throttle stop screw, if you turn it more than a 1/2 turn in either direction, you better check your installation.
3. Yes you do have to trim the intake manifold opening, mine had a 1/8 lip around the base and it does have a profound effect on air flow, enough to cancel the gains of doing the conversion. I used a die grinder with a wide fluted aluminum bit, on the vehicle wuth rags stuffed in the intake runners. A shop vac to remove the filings was used and make sure all filings and rags are removed. I trimmed the hole to the size of the gasket (4.0 and 2.5L gaskets are the same).
4. The PCM's adaptive memory after 100 miles of driving was practically unchanged after the swap meaning the PCM saw no ill effects from the swap. Keep in mind that the MPI fuel injection is a speed/ density based system and does not see an increase in airflow like other systems that use a mass air flow sensor, instead it sees changes in MAP value and intake temperature (density in the intake manifold) crankshaft speed and throttle position, coolant temperature in all modes plus the O2 sensor at idle and part throttle and then using complex alogrythims calculates the injector pulse to provide the correct fuel/air raio. For all practical purposes you do not need to worry about it, the computer seems to compensate for the swap with no problems.
5. For those of you who still feel the need for more fuel, you can try injectors from a 4.0L engine. These run approx. 10% richer, single cylinder displacement is about 10% larger on a 4.0L, so these will work good if you need more fuel delivery without screwing around with the pressure regulator on the fuel rail (91-95 only, TJ's regulator is in the fuel pump). The PCM will only compesate for the added fuel in closed loop operation only (idle and part throttle)!
I did this swap months before I even came across this site (my own idea) in search of more power, knowing what it would take to install a 4.0L in my Jeep, even with the resources available, and I can tell you I am very satisfied with the results. I hope the information I posted is useful and can be used to your advantage.
Ken AKA: lonewolf1061
Some great posts here, I am glad to see that people are experimenting with new things to try and extract some power out the the 2.5's. A very popular topic seems to revolve around puting in bigger fuel injectors. I am willing to bet that in the majority of cases that is a waste of money. The stock injectors are more than capable. They are providing enough fuel in my supercharged application so there is no way that a normally aspirated motor would be hurting for fuel. Has anyone actually taken your O2 sensor readings? I am willing to bet that if you do you will find that you are getting enough fuel. Just slapping in a open air filter will not cause you to run lean. Take some readings before wasting you money on bigger injectors.
Regarding injectors, in my own trials, I found that the stock injectors work very well. They have enough fuel flow for most naturally aspirated engines. I tried 4.0L injectors with mixed results, good part throttle response, but a little rich at full throttle, seems the stock injectors produced more power at full throttle. As far as blown/ turbo applications stock injectors are probably borderline.
Blown YJ did you make provisions for the increased manifold pressure? I don't know what boost you're running, but if you run stock injectors, you need to raise your fuel rail pressure to compensate for the boost you're using. 10 lbs. of boost needs an additional 10lbs. at the fuel rail to compensate to negate the effect of the positive manifold pressure, so fuel flow remains a constant value. Do you use an intercooler? You may be running a little lean. Lean mixtures will produce power, but at the expense of cooling and engine life. Detonation can ruin your day. Check your spark plugs for signs of overheating.
TJ injectors on a YJ I don't recommend, beause the electrical connectors are different, finding the plugs to fit are damn near impossible to get. Also YJ fuel rail pressures run at 29-39 psi. TJ fuel rail pressures are run at a constant 50 psi. If you use a TJ injector on a YJ you would run lean cause you're running 10lbs less fuel pressure. And I think the O ring sizes are different, I never really took the time to compare the two side by side. So for YJ's stick to 4.0L YJ or ZJ injectors and for TJ's use 4.0L TJ or WJ injectors.
Jeffy, you got me on cams because the only one listed is the stock repacement, everything else is discontinued. If any one has a line on aftermarket cams, let me know. You may try Erson, Crane,Clifford etc.
Gear Poet, yeah things can get complicated. If you feel comfortable grinding your intake on the vehicle, ok. What I did was stuff shop rags tightly inthe runners. Any lip or protrusion will hinder airflow. That is why match porting of yourintake to cylinder head can be a big plus, so can the header/ex manifold. Anytime you reduce turbulence in any form you increase airflow. A 3 angle valve job can really help flow at low valve lifts. You would be amazed at the increases you can get and still use the stock cam. The throttle body spacer is a good idea, straightening the airflow increases the ram effect into the plenum, but the helix designI have reservations about it. Reason is that it would only effect the outer periphery of the air column, not enough time to spin the entire column of air. A Tornado device would be more effective since it covers the entire air column. Also being under the throttle plate the helix would only be effective at full throttle only. since a partilly closed throttle would change the airflow direction past the spacer. Also remember, that airflow in the intake is not a steady flow in. It is a pulsing flow with sharp reversions in the opposite direction in the intake runners when the intake valve closes. The common plenum does soften those pulses, but it is still present at WOT. That is why I think the helix design is not that effective, even though some poeple swear by it, I would prefer some kind of smooth bore spacer. I will probably get feedback on this , but I am tryingto look at this from all possible angles.
Ken AKA: lonewolf1061
I almost forgot to tell Blown YJ that your O2 readings are only valid at idle and part throttle….in other words when your supercharger is not boosting, so you don't know what your fuel mix is at boost. I assume you have a YJ 91-95, correct? If so the PCM runs only in closed loop at idle and part throttle up to 10in vacuum, all other modes i.e. cold starting, acceleration, WOT,decelleration run open loop on a pre determined program. The only sensors that come into play are all sensors except the 02. So if you are reading your 02 sensor with a scanner and it shows -4.5% shorterm adaptive and -8.0% longterm adaptive (typical normal readings used as example only) what you are seeing is what a stock engie sees at idle, giving you no indication what you are running at boost. You need to check your plugs for signs of overheating. Running lean at even moderate boost (5-6psi)can cause melted piston tops and damage due to detonation. The best way I've seen is to raise your fuel pressure to conteract the effect of positive pressure in your intake by using a fuel pressure regulator that responds to boost pressure and a high pressure fuel pump to keep up with the demands (stock fuel pump puts out 42psi max) I may be jumping the gun here but you may have installed a complete kit which addresses the issues here. Anyway good luck and hear from you soon.
Ken AKA: lonewolf1061
I have a 95YJ and did the 4.0 swap on friday. Discovered (as someone mentioned before) that the AIS housing needs to be swapped also. With the 4.0 housing, the jeep was idling at 2,000. My check engine light came on too. Well, I put the 2.5 housing on the 4.0 TB and put it all back together under the hood. Took the Jeep for a test drive and it was running like sh!t. The jeep idled correctly but at around 2,000 rpm's, she would buckle a little before picking up more speed. She's also getting realy bad gas mileage and no matter how much resetting of the computer i try, the check engine light stays on…
Ok, im thinking that maybe something found its way into the manifold and therefore into the engine. That would be a bad thing. This weekend, im gonna take the manifold off and look for whatever fell inside. Has this happened to anyone? What did you do?
The reason I think that something fell inside the manifold is because I went camping the next day and after attempting to reset the computer again, I just went ahead and put the old TB back in. In the process of doing that, i managed to lose the oring for the AIS and ended up using the end off a baloon. Things just arent looking up for me, are they?
Anyways, to further support my conclusion, the jeep is running almost the same (sh!tty) with the old TB than it was with the 4.0 TB. Before and after the losing of the gasket, with and without the 4.0 TB.
(The problem ended up being a partially pulled wire on the tps.)
What kind of performance can you expect from a 248 deg. cam…….more torque.
Cam profiles are hard to understand, you would think that a 270 deg. cam is better, but bigger numbers don't always give better performance under certian conditions. Take a Jeep w/ 33” tires and stock 4.10 gears, a stock cam does not have a lot of torque under 2500 rpm. Peak torque occurs at 3450 rpm with a stock engine. The 248 deg. cam has a broader power band from 1100 to 5400 rpm, more pulling power (toruqe). I can attest to this because I had a stock engine w/ 33” tires and it had no power below 2500. The big difference is the overlap, 46 deg for the stocker and 32 deg for the performance cam, result less exhaust gas dilution of the intake charge with less overlap, meaning higher brake mean effective pressure (BMEP) sooner….more torque. Ever noticed why Jeep engineers didn't have to fit EGR systems to the 2.5L and 4.0L MPI engines? The extra overlap of the cam caused more intake dilution, reducing BMEP, which reduced formation of oxides of nitrogen (NOS) and as a side effect, less power and fuel efficiency. Therefore a performace torque/RV grind is an excellent choice.
Usually choosing a cam grind is the LAST thing to pick, other variables play an important role in how the cam works….intake restrictions, exhaust sytems… especilly headers since their legnth has a profound effect on where the torque band rpm's set up, port and valve sizes, compression ratio, ignition timing, etc. All these variables need to be taken into account and the type of driving you do. If you have a heavy Jeep with big tires (like mine), a short duration cam with moderate lift is a good choice, if you are into stop light racing, a longer duration cam with high lift is your choice…just be sure that the rest of the engine matches, such as balancing and valve train mods $$$, since the higher rpm's put a dramatic strain on your parts.
I just ordered the Mopar Performance 248 deg cam for my 2.5L and I have an extra head to send out to get a peformance valve job with some minor porting work, just cleaning up the casting flash and to smooth the ports out a little. Once I am done, I will let you know how it turns out.
Ken AKA: lonewolf1061
Thanks for you post. I am very familiar with forced induction. Let me answer a few of your questions. I do have an external rising rate fuel regulator and currently I am at 7 lbs of boost. No intercooler but working on a water injection system. Even with this, tbe stock injectors are meeting the fuel demands. I disagree completely on the 02 sensor readings. It most definitely gives you the ratio whether you are at idle or at full boost. I had my jeep at the dealer for a diagnostic and verified and mapped the readings from my o2 sensor guage to what the computer was seeing. Under WOT you see readings in the .85, which is where you want them to be. I would agree that running lean is not the best but it does give you a little more power. As long as you are monitoring for knock and also checking the temperature of your exhaust gasses( at the manifold) you can stay out of trouble. I also have a knock sensor, which basically reatards the timing by a couple of deegres if it sences knock, another precaution you can take. My only concern is that people are going to put in bigger injectors in thier 2.5 and the end result is going to be a loss of power, unless you are running lean there is no need for additional fuel.
The cam I got is a Mopar performance cam directly from Jeep parts department (remember I work at a Jeep dealer). There are only about 8 or so of these puppies left, I had to get one shipped from from another dealer. There are none at the warehouses. If you want the 248 deg cam, you better hurry and order one tommorrow. The other 2, the 240 and the 256 deg cams are still available with about 50 or so of each. I guess the 248 deg cam is a popular grind. The cam I got specs out at: 248 deg duration, intake and exhaust .440” valve lift 108 deg lobe centerline
Pricing will vary between $100 to $130 depending on the dealer you buy it from.
Dyno time is big $$$, so I will stick to the seat in the pants method. If you know your vehicle real well, you'll know if you made an improvement or not.
As far as the O2 readings at full throttle go, the O2 sensor still switches, you can see it on the DRB II or III, but it is not part of the equation when at full throttle. How to check is to read your short term adaptive memory, you will see it change as you vary the throttle opening slowly, just as the O2 does. Now drive the Jeep and watch what the short term does… idle and part throttle will show a + or - value in percent, stand on the throttle and it will go to 0%…default settings programmed in the PCM. When you return to idle or part throttle the short term starts switching again and the PCM goes back to closed loop. Your long term memory is acummlated over 10 or more miles of driving. Long term memory gives an indication what your motor is doing, a + value means thePCM is giving the injectors a longer pulse width (more fuel) motor is running lean, a - less fuel motor runnning richer. I use the DRB III with the supercard over the II because it is more reliable when checking the memory of the PCM.
I still have the original factory training manual for the 91 2.5 and 4.0L MPI engines which tells you the same thing I explained to you in detail. I work with these engines on a daily basis, drivability and electrical problems at the dealer level.
Ken AKA: lonewolf1061
Well…don't know what the emissions are yet, don't have the cam installed yet…I don't even have it yet from UPS. The head is still at the machine shop getting a 3 angle valve job and a cleaning up. I still have to get all the odds and ends such as gaskets, timing chain, tensioner, etc. I want to make sure I have everything on hand when I start this project. As far as emission testing I can test for CO and HC emissions, but don't have the equipment to test for NOX. Kind of irrelevant for me since Florida stopped emission testing in all counties about a year ago. I would probably guess CO and HC emissions would remain the same or even less, since the engine is running more efficiently, but NOX would increase due to higher combustion pressure and temperature.
The Mopar Performance catalog shows the 240 cam's basic power band from 900 - 5200 rpm, good for automatics with big tires, the 248's 1100 - 5400 rpms good for a 5 speed with big tires. The 256 1200 - 5600 rpms, good for smaller tires. As you can see, the longer duration cams shift the power band to a higher rpm range, which is not good for big tires, low rpm use such as offroading especially rock crawling. You want a motor that pulls good from idle and produces predictable power throughout the powerband with no sudden bursts. A mud bogger can use a higher rpm range since you run full tilt through the mud to keep yor tires spinning to keep from sinking. See how different cam profiles are better for different applications? You need to know what you are going to use your vehicle for to pick the right cam. I picked the 248 deg cam because I run 4.10 gears with 35” tires and a 5 speed, if I had an auto (yuk) I probably would have gone with the 240. With the 4.0 throttle body, mild head work, and header it should produce some good power and a little better fuel efficiency over the stock cam. Of course 4.56 or 4.88 gears wouldn't hurt either.
Ken AKA: lonewolf1061
For anyone who is interested, Rubicon Express has just released an anodized aluminum throttle body that has a 62mm opening for $299. They claim this is an introductory offer.
Posted 6/24/2002 by soulknight