2.5L Power Upgrades

[Tyler Tafjen]

I'm new to the site and recently picked up an 86 2.5L with a 5 speed and 4.10 gears. I know its a 4cyl but it just doesn't have the power to make it up some of the hills in town anywhere close to the speed limit. Are there any upgrades (other then motor swaps) that will increase the power and performance? Right now it is fully stock, but I'm planning on putting on a 3" lift and 31s before the winter starts here. I have heard about throttle body swaps and different injectors, but i don't know where to start. Any help would be appreciated.

[87Chief]

Probably the best for performance would be gearing in your axles.. Not much you can do with a 2.5L 

[TheDirtyJeep401]

I'm on the search too. Right now I'm looking into bigger injectors. I hear you can take a 4.0 throttle body and out it on a 2.5, havent tried it yet. I also think that switching to a electric fan would help.

 

Unless you want to spend like $3000 to get a turbo kit for it :brows:

[Oyaji]

Stock power should be at least adequate to handle any paved road in the country.

 

I see you live in California. An emissions check is a pre-sale requirement there, right? Passing results from a proper check would indicate that the engine is running not too far off its stock performance... provided a proper check was done.

 

 In case it wasn't done, make sure it is in a good state of tune. Reading the spark plugs can tell you much.

 

A partially plugged catalytic converter can drastically cut power output. Have a "test pipe" fabricated (or fab one yourself) and bolt it in to replace your cat. It is (or was and still should be) legal even in your state, and you might like the results so much that you decide to run quite a long test.  ;)  (Being prepared to show the last week's data - for instance, fuel economy data - might be a good idea in case you get caught. Having more than a week's data on hand might be hard to explain though! :D)

 

Just to cover all the bases here, I should ask - you are down-shifting that 5-speed to keep the revs up for the hills, right?

[Jeep Driver]

I bought mine about two years ago, the previous owner had just rebuilt the engine but reinstalled all the old sensors. It ran well but it didn't feel smooth and I could tell something just wasn't right, the first thing I did was to through the process of replacing all the sensors and sending units, TPS, CPS, IAT, coolant sensor in the intake, O2 sensor.........all of them.....

Tuned it up also......plugs, wires, caps,,,,,,,,etc.......

 

The single greatest gain was to grab some cold air and get rid of that POS air box, with the radiator out of the way........easy to do on the 2.5. And get rid of the catalytic converter...gotta go.

 

I even went to an electric fan to get rid of the mechanical.

 

Going through you electrical system is a MUST......all new cables and grounds....ect.......a MUST do!

 

 

My engine runs smooth and quiet, at idle, I cannot hear it run nor feel it run........most of my hearing is shot anyway.

 

 

 

 

Go to the Fiero performance sites.....S10 blocks and cranks.....flow through heads.....headers........ignitions.........all performance builds........but plan on spending $7K+++++ to get any kind of power out of your 2.5.

 

 

[Jeep Driver]

 

 

 

http://ironduke7.tripod.com/IronDuke.htm

[cruiser54]

Yeah, but our Jeeps aren't Pontiacs.....

[Jeep Driver]

My understanding is that the AMC 2.5 started out as the GM Iron Duke........block should be compatible with bell housing.

 

 

Edit:

Further, I'm pointing in a direction- This is the extent that one goes to to get performance out of 30 year old 4cyl.

 

Following the research provided......they go extensively into which blocks, cranks, heads...etc.

 

 

I did not say this is your solution or end-all...........I said, look here........

[dasbulliwagen]

The ONLY thing the AMC 2.5 has in common with the Iron duke is the bellhousing bolt pattern... nothing else. The injector and throttle body swap only applies to 91 and newer models with port injection. You could swap to the newer injection system completely, but that would involve a complete engine compartment wiring swap, new computer and dash harness and guages as well. If youre going to do all that, may as well swap to a 4.0... would be a similar amount of work to do. As was said, cold air intake, electric fan swap, free flow converter and exhaust, ground cleanup, maybe a throttle body spacer, though there really isnt room for that already and its effectiveness is up in the air though I think only because port injected guys wouldnt see any benefit from one. Beyond that its either cubic dollars or cubic inches. Good luck.

[Oyaji]

Ever since they came out some years ago, I have been telling folks that cold air intakes are a "snake-oil" hokum product that does not produce the power gain claimed in excess of stock, and in fact is potentially harmful since engines so equipped are vastly more susceptible to ingesting water that can cause hydro-lock (which stock systems are designed to circumvent). Few would listen, as common sense would lead one to believe that such should work as advertised.

 

But folks don't have to take just my word for it, because nowadays there are heaps of exposés - here is one:

 

[dasbulliwagen]

I agree, most stock intakes are already COLD air, but I think most benefit is had through smoothing the air flow out making it easier to get into the motor. The stock 2.5 airbox has a restricter in it too that I think is removable.... that would help a little if you don't go full new COLD air intake. Ive done the COLD air intake, the electric fan conversion, and gutted my cat conv, and installed a flowmaster 50 series muffler. It made a little difference, but I don't think youll see enough power increase to get what you want out of it. I love my 2.5, but it sounds like the only thing that will really help you is a complete 4.0 swap.

[Jeep Driver]

I live in the mountains.

 

There is one incline that is measurable, 1.5 miles long, perfectly straight and even, at about 6%.

 

When I first got my truck it would not manage that incline in 4th gear, no matter what speed I hit it at, I had to drop to 3rd and ream it out.

 

After improvements, If I begin the incline at 45 in 4th it will maintain, if I hit it at 50, doesn't even whimper.

 

 

Bear in mind I pull a 3000lbs trailer around during mowing season.

 

 

 

You can dismiss the intake all you want........

 

 

Edit: I also went from 235-75-15s to 31s........significant increase in tire size for the 2.5.

 

Edit again:

As long as I maintain 70-80 on the interstate in 5th......very smooth and no lack of power, incline or not.

[Oyaji]

I agree, most stock intakes are already COLD air, but I think most benefit is had through smoothing the air flow out making it easier to get into the motor. The stock 2.5 airbox has a restricter in it too that I think is removable.... that would help a little if you don't go full new COLD air intake. Ive done the COLD air intake, the electric fan conversion, and gutted my cat conv, and installed a flowmaster 50 series muffler. It made a little difference, but I don't think youll see enough power increase to get what you want out of it. I love my 2.5, but it sounds like the only thing that will really help you is a complete 4.0 swap.

 

Roger that.

 

It's worth keeping in mind that the primary restriction contributing to pumping losses in any gasoline engine is the throttle plate, which for almost all driving is mostly closed. Best gains to be had would come from reducing restriction in the exhaust, but that would be most pronounced for high load demand when flow is increased, same for reducing restriction in the intake.

[92tanMJ]

IMO the bottom line is it's a 2.5 it is gutless and always will be...and that lift isnt going to help.

IMHO the only way you're going to get the power you want is a 4.0.

 

 

        I agree, most stock intakes are already COLD air, but I think most benefit is had through smoothing the air flow out making it easier to get into the motor. The stock 2.5 airbox has a restricter in it too that I think is removable.... that would help a little if you don't go full new COLD air intake. Ive done the COLD air intake, the electric fan conversion, and gutted my cat conv, and installed a flowmaster 50 series muffler. It made a little difference, but I don't think youll see enough power increase to get what you want out of it. I love my 2.5, but it sounds like the only thing that will really help you is a complete 4.0 swap.

     

    Roger that.
    It's worth keeping in mind that the primary restriction contributing to pumping losses in any gasoline engine is the throttle plate, which for almost all driving is mostly closed. Best gains to be had would come from reducing restriction in the exhaust, but that would be most pronounced for high load demand when flow is increased, same for reducing restriction in the intake.

False. The best gains are when you reduce the restrictions in both (but too much). Firstly, air can only come in as fast as it can go out and it can only go out as fast as it's coming in. Secondly, (I'm just saying this in general not to you- I realize you said reduce and not eliminate) back pressure actually helps a motor run, you need it. If you have ever ran a 4.0 on just straight headers you'll one know they're loud as heck lol but other than that the butt dyno can actually feel a loss of power.

[jimoshel]

I feel the 2.5 is an excellent engine and is more than adequate for normal, everyday driving. This coming from and old school believer of cubic inches rule. I think I'm one of the first guys around to stuff a 472 CI Caddy engine into a CJ5.  My DD is a '87 MJ with the 2.5 and a AX4. I consistantly push it down the highway at 75-80 MPH and get 17-21 MPG.This is just the truck. Minimal load on truck, no trailer. If you have a 2.5 that is not performing the way you think it should follow the above offered advice about checking CAT, intake filter, etc, etc.

[Oyaji]

IMO the bottom line is it's a 2.5 it is gutless and always will be...and that lift isnt going to help.

IMHO the only way you're going to get the power you want is a 4.0.

 

 

 

        I agree, most stock intakes are already COLD air, but I think most benefit is had through smoothing the air flow out making it easier to get into the motor. The stock 2.5 airbox has a restricter in it too that I think is removable.... that would help a little if you don't go full new COLD air intake. Ive done the COLD air intake, the electric fan conversion, and gutted my cat conv, and installed a flowmaster 50 series muffler. It made a little difference, but I don't think youll see enough power increase to get what you want out of it. I love my 2.5, but it sounds like the only thing that will really help you is a complete 4.0 swap.

     

    Roger that.

    It's worth keeping in mind that the primary restriction contributing to pumping losses in any gasoline engine is the throttle plate, which for almost all driving is mostly closed. Best gains to be had would come from reducing restriction in the exhaust, but that would be most pronounced for high load demand when flow is increased, same for reducing restriction in the intake.

False. The best gains are when you reduce the restrictions in both (but too much). Firstly, air can only come in as fast as it can go out and it can only go out as fast as it's coming in. Secondly, (I'm just saying this in general not to you- I realize you said reduce and not eliminate) back pressure actually helps a motor run, you need it. If you have ever ran a 4.0 on just straight headers you'll one know they're loud as heck lol but other than that the butt dyno can actually feel a loss of power.

 

 

Roger - on headers you need to run at least a section of exhaust downstream from the collector to get benefit. That's not so much to add restriction but to smooth out flow and to provide a section of pipe to take advantage of the momentum of the gas in the flow (plus to use the momentum of the exhaust gas pulses from each cylinder to help scavenge/draw flow from the others).

 

It's the same principle as the hydraulic ram effect. Simple example: notice the pulse you get from suddenly releasing the handle of a garden hose spray nozzle - you feel the surge as the momentum of the moving water that wants to keep moving but can't because you closed the valve at the end of the hose. The moving column of water inside the garden hose has mass that has inertial momentum and wants to keep moving.

 

Any mass in motion has that same inertia, gases included. That's why you get benefit from having a section of pipe downstream from a header. It gets more complicated than this simple explanation, but suffice it to say that you can tune the power increase for engine speed (RPM) by changing the pipe length.

[TheDirtyJeep401]

I bought mine about two years ago, the previous owner had just rebuilt the engine but reinstalled all the old sensors. It ran well but it didn't feel smooth and I could tell something just wasn't right, the first thing I did was to through the process of replacing all the sensors and sending units, TPS, CPS, IAT, coolant sensor in the intake, O2 sensor.........all of them.....

Tuned it up also......plugs, wires, caps,,,,,,,,etc.......

 

The single greatest gain was to grab some cold air and get rid of that POS air box, with the radiator out of the way........easy to do on the 2.5. And get rid of the catalytic converter...gotta go.

 

I even went to an electric fan to get rid of the mechanical.

 

Going through you electrical system is a MUST......all new cables and grounds....ect.......a MUST do!

 

 

My engine runs smooth and quiet, at idle, I cannot hear it run nor feel it run........most of my hearing is shot anyway.

 

 

 

 

Go to the Fiero performance sites.....S10 blocks and cranks.....flow through heads.....headers........ignitions.........all performance builds........but plan on spending $7K+++++ to get any kind of power out of your 2.5.

 

 

HAve any more pics of that intake? Looks interesting

[xjrev10]

My last 4 cylinder MJ had no trouble doing 70 mph in the highway with a snowmobile or ATV in the box..

[92tanMJ]

Roger - on headers you need to run at least a section of exhaust downstream from the collector to get benefit. That's not so much to add restriction but to smooth out flow and to provide a section of pipe to take advantage of the momentum of the gas in the flow (plus to use the momentum of the exhaust gas pulses from each cylinder to help scavenge/draw flow from the others).

 

It's the same principle as the hydraulic ram effect. Simple example: notice the pulse you get from suddenly releasing the handle of a garden hose spray nozzle - you feel the surge as the momentum of the moving water that wants to keep moving but can't because you closed the valve at the end of the hose. The moving column of water inside the garden hose has mass that has inertial momentum and wants to keep moving.

 

Any mass in motion has that same inertia, gases included. That's why you get benefit from having a section of pipe downstream from a header. It gets more complicated than this simple explanation, but suffice it to say that you can tune the power increase for engine speed (RPM) by changing the pipe length.

FYI, I just disagreeing with what was in bold.

 

 

 

Have any more pics of that intake? Looks interesting

 

Have you ever seen the cowl intake mod?

[TheDirtyJeep401]

 

Roger - on headers you need to run at least a section of exhaust downstream from the collector to get benefit. That's not so much to add restriction but to smooth out flow and to provide a section of pipe to take advantage of the momentum of the gas in the flow (plus to use the momentum of the exhaust gas pulses from each cylinder to help scavenge/draw flow from the others).

 

It's the same principle as the hydraulic ram effect. Simple example: notice the pulse you get from suddenly releasing the handle of a garden hose spray nozzle - you feel the surge as the momentum of the moving water that wants to keep moving but can't because you closed the valve at the end of the hose. The moving column of water inside the garden hose has mass that has inertial momentum and wants to keep moving.

 

Any mass in motion has that same inertia, gases included. That's why you get benefit from having a section of pipe downstream from a header. It gets more complicated than this simple explanation, but suffice it to say that you can tune the power increase for engine speed (RPM) by changing the pipe length.

FYI, I just disagreeing with what was in bold.

 

> 

 

Have any more pics of that intake? Looks interesting

 

Have you ever seen the cowl intake mod?

 

I don't believe I have.

[92tanMJ]

 

 

 

 

> 

 

Have any more pics of that intake? Looks interesting

 

Have you ever seen the cowl intake mod?

 

I don't believe I have.

 

One of the better ways ive ssen it done; http://www.jeepforum.com/forum/f11/another-cowl-air-intake-write-up-741764/

[Tyler Tafjen]

Thanks for all the input. Got to get some $$$ before i can do anything but ill defiantly keep this in mind.

[Jeep Driver]

 

AMC/Jeep 2.5L four cylinder, ported head, YellaTerra roller tip rockers, MP cam 248/248-32-.440/.440(Phase II), Banks Torque Tube header, '95 MPI intake, will run '93 OBDI MPI, built by Duffin Engine Service, SATX.

 

http://4bangerjp.com/forums/index.php?topic=9530.0

[dasbulliwagen]

There is a TON of good info there at WWW.4bangerjp.com for the 2.5. I joined over there a week or so ago. There are a few people over there that are literal encyclopedias on these things. From cold air kits to turbo and super charging, big valve heads, porting, rockers... its all there. O can't believe I hadn't heard of it before now.

[JeepcoMJ]

I'm on the search too. Right now I'm looking into bigger injectors. I hear you can take a 4.0 throttle body and out it on a 2.5, havent tried it yet. I also think that switching to a electric fan would help.

 

Unless you want to spend like $3000 to get a turbo kit for it :brows:

 

Am I the only one bothered by this statement?

 

The 86-90 4 cylinders have NOTHING in common with the 4.0.  You cannot swap the throttle bodies or any parts in between for the one pure and simple fact that the 86-90 4 cylinder is throttle body fuel injection.

 

The statement of popping a 4.0 throttle body only applies with like-year 4 cylinders and 4.0's from 91 and up, because they are both multi port fuel injection.