ileftmypics

I need advice. I have a 2001 Jeep Cherokee Limited. It has the "Up Country" upgrade from factory which includes a locker in the rear, 1 1/2" Lift, bigger tires, trans cooler, cooler thermostat.

I'm looking for more power for the street, not going to race anyone, just want it to be snappier. Don't want to have to put my foot to the floor to pass anyone. I will never go mudding in this vehicle or any off-road shenanigans. I am not lifting the vehicle either. No disrespect to all of you who do this, and your Jeeps look bad-*** and do some amazing stuff, it's just not my thing.

The motor has a slight knock and the oil pressure is at 15, so the motor will have to come out someday. So, Stroke It or Rebuilt with all the aftermarket goodness, header/exhaust, cold-air, chip, injectors, throttle body, polish port head, match the intake. Possibly a cam? You guys get it. Can't wait to hear some ideas!

I would like to note that the body of my Jeep is straight. The gentleman before us did some weird ****. The transmission is being rebuilt as we speak because someone towed over-capacity with it many times, and my clutches are fusing together. Having the boys put a mild shift kit in it, and they are putting clutches that will engage and disengage faster. No need for a stall, as the Jeep has a stall already.

caged

i think you wouldn't be happier if it was stroked.

so i say stroke it

BRN2KL

If you are looking for better response out of an engine, stick with the factory 4.0. Im not saying dont do some upgrades, I just wouldnt go through the effort to stroke it. If you can find a descent machine shop in your area, have them punch the block for bigger pistons and deck the head mating surface. Also have the machine shop check the crank and rods for concentricity. If the machine shop is worth what you are paying them, they will suggest all of this.

Next, have the machine shop clean up the short side radius of the intake and exhaust runners on the head. "Pocket porting" is also a great idea. Basically removing casting marks and a slight polish to the runners in the head.

Also have a valve job done on your head. Have the valves back cut at about 30 degrees. If your machine shop doesnt know what you are talking about, leave them and in a hurry.

Next get a good cam. Erson cams are good and about half the price of Comp Cams. That makes Erson great imo. The head that has been work and cam will make a world of difference. If you move more air in + more air out= more power.

Gasket matching and all of the rest of that stuff works great on a race application where you are trying to run in a class. But for the money you will spend and the slight response that you will get from all of the gasket matching work, larger valves, and so on, you could install a blower and be done. There is always that option... and if you are just on the street, a turbo is not outside the realm either.

Hope this helps

connolcj

I would also like to hear more on this as I'm in a similar situation. I want to learn more about it before in dive into it.

BRN2KL

Were you asking this of me? If so, there is much we can talk about, but more specifically what do you want to know or what do you have questions about? I don't know everything, I do know a little, and will be happy to share with you what I do know. Lemme know

connolcj

I was just wanting to hear more on the topic as a whole. Not necessary just you I want to hear others opinions and experiences. I have a 93 cherokee country with 180000 miles and will be needing some help soon in the engine department. I know a lot about suspension work but engines are another story. Thanks for the inputs.

BRN2KL

Here's to keeping the topic going! I too would love to hear others input!

There is no replacement for displacement. So increased displacement (stroked) or more cubic inches will have more POTENTIAL for power than smaller (factory) displacement. Boring a 6 cylinder and increasing overall displacement of 4 cubic inches, everything else being the same, will have little effect on overall power output.

That being said, if you increase 4 cubic inches, and reduce the mass of your rotating assembly, then overall power output will increase. Increased by how much? I am unsure.

In addition, if you take that same increase of displacement, with a reduced rotating mass and increase the amount of air into the cylinders, then overall power output will increase. This is the concept behind forced air induction. The idea is to increase the volume and density of the air in the cylinders on the intake and compression stroke. An increase of volume can be achieved by increasing the length of time that the intake valves are open. This is where increased lift cams come into play. Besides lift, duration of the cam lobe, or how long the valve stays open can be a benefit. One disclaimer here: DO NOT BUY THE CAM WITH THE BIGGEST LIFT AND THE LONGEST DURATION FOR A STOCK OR MILD REBUILD. Be realistic about how, where and what you drive. Know what RPM range you most often operate your vehicle. Ask a professional engine builder, or cam builder for their recommendation. Don't call summit. Yes I'm a hater!

If we move forward just on the "Air In" portion of engines we could spend hours talking about ways to improve air flow and volumetric efficiency. Some topics could be porting of the intake runners on the head. Gasket matching or port matching of the intake and head. Increased valve size of both I/E valves, which may or may not increase shrouding. Back cutting of valves, static vs dynamic compression ratio, the scavenging effect of the exhaust side of an engine and "back pressure," which is kinda like voodoo. As you can see there is copious amounts of information to be understood before informed decisions can be made.

There are other concepts that can be calculated on paper or measured. Air to fuel ratio is mission critical. To lean and you scorch the cylinders. To rich and you loose power and waste fuel. But optimal air/fuel can be measured and determined.

Oh and we haven't talked about ignition timing. Or gearing for optimal RPM range. Or parasitic loss due to the valve train. Or torque converters and stall speed and how that can effect overall performance. And how cam selection can effect everything that we have mentioned or failed to mention.

I hope I have left the door open for input from some of the great engine minds that read this forum. I am personally looking for some folks that have experience with stroking the 4.0 and getting their input on what went right, or wrong and what they would do differently.

NOTE: I have made some generalizations here in saying that power will increase. This statement is made in comparison to a bone stock factory engine and the assumption that both the factory engine and the theoretical "rebuild" are both running at optimal levels and were of the same original configuration. So dont ding me with some minor freaking detail about how a 283 that you had made 1200HP. If you wanna make a statement like that, get bent!

Lets hear from some others...