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Help me build a "Four O+"


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This thread stems out of my build page, to the technical forum so I can get the help of CC.

 

Objective: I am looking for help in creating a build sheet/list for a modified 4.0L. This motor will be based upon a 99 XJ block and will be going into my Comanche, which will be a daily driver turning 4.10's and a 30/31" tire.

Goal: I want to pull more power out of the motor yet maintain fantastic drive-ability and reliability without the need for premium fuel.

 

The motor will be getting a thorough going through and rebuilt by the same shop who simply rebuilt my rubi's 4.0 in '03. I am thinking work along the lines of bearings and seals/gaskets, cam, pistons, porting, etc. Possibly a header as well. At this point, I am not sold on a stroker. It seems in order to build a stroker to be as reliable as a stock 4.0, it is not cheap ($2,500K in parts with no guarantee it will run on 87) even with the DCR between 6-8:1.

 

I call on you to help me assemble a build sheet for the Comanche's new heart :yes:

 

Build Sheet (updated as decisions are made)

Block

Crankshaft: Stock

Connecting Rods: Stock

Pistons:

Oil Pump: Mopar High Performance

Gasket Set:

Timing Set:

 

Head

Head Gasket: Mopar/Victor 0.043"

Camshaft: COMP Cam 68-231-4

Lifters:

Valve Springs: Mopar High Performance P5249464

- Retainers: Mopar High Performance P4452032

- Locks: Mopar High Performance P4529218

Rocker Arms:

Head Bolts:

 

Additional

Injectors:

Header:

Head Porting

Balancing

Valve Job

 

I don't anticipate the need to specify bearings and seals, as I will leave that to the builder.

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are you keeping the Renix injection?

 

personally I'd keep everything as stock as possible, but with a hotter cam and a lot of porting work on the intake and exhaust, valve job etc. maybe look into the late model 4.0 intakes as they flow more air. also some 5.0 injectors would be thrown in :D

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are you keeping the Renix injection?

 

personally I'd keep everything as stock as possible, but with a hotter cam and a lot of porting work on the intake and exhaust, valve job etc. maybe look into the late model 4.0 intakes as they flow more air. also some 5.0 injectors would be thrown in :D

 

Yes, late model intake, early h.o head (they also make an awesome flowing aluminum head good for like 30-40hp), 5.0 injectors, a set of headers, and you'll get a nice exhaust note and reasonable power on 87 fuel without breaking the bank or hurting drivability.

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I will be starting out with a 99XJ motor with OBDii. See my build for more information. :D What the motor becomes will be the direct result of this thread.

 

Does anybody have cam recommendations? I have been studying the specs of several cams out there. The problem is, while I understand the numbers regarding lift/duration/etc I do not know how the subtle differences will affect the engines performance.

 

Comp Cams categorizes their 4.0 cams for their areas of improvement. I *think* for my application a slight improvment down low and a great mid range would be right for a DD. I suspect the truck will be turning 2,300rpm at 70mph.

 

I will bore it .030 over and stick new pistons in it for piece of mind. Selecting a piston seems like quite a chore with all of the options out there. I am looking at maintaining a close to stock dish volume. Although, I could drop it a little and deck the block to drop the quench distance to prevent detention. This would also impact the type of cam that goes in it. Looks like I might need to run a few DCR calculations and are what happens.

 

Gosh I would love to pick up that aluminum Hesco head, but they are high dollar!

 

I am not really aiming for a particular exhaust note. With these small improvements combined with the XJs larger exhaust pipe, it should sound great.

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Since you are going OBDII, you will now have the option of having complete control over the '99XJ PCM's fuel and timing maps using an SCT handheld tuner. Granted, you will have to find a tuner knowledgeable with modified 4.0L engines that can get you a custom fuel and timing map. The nice thing about the tuner is that you can get up to three different tunes and each one can be catered to a specific octane gasoline. You can still build up your stroker motor, if you wish, and basically adjust your timing and fuel maps so that it will not knock and ping at wide open throttle on 87-octane, but you'd be robbing it of precious HP and TQ. You can also have a 93-octane tune that will allow you to get the power back if you want it. If you went this route, I would highly recommend a wideband oxygen sensor mounted directly before the catalytic converter with a gauge somewhere in your interior that you can keep an eye on if you went this route.

 

If you'd like - I can ask the guy who did my tunes for my 5.9L V8 Magnum if he has any experience tuning the 4.0L engines. The price for the tuner + 3 "canned" tunes was about $265. An additional $100 for unlimited tunes for when you modify the engine down the road and need to change the fuel maps and timing for optimal power.

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Terra - Thank you for the information. I am not sure I want to build a motor that requires reflashing the PCM. But I will certainly keep your suggestions in my mind.

 

This evening I have been running a few desktop calculation with varying pistons and camshafts. I am beginning to better understand the correlation of all the numbers and what they do.

 

I do have a question about the cams for sale. It seems that most of them are only posted for up to a '97 4.0 block. I will be using a '99 block. I thought all 4.0L cams would interchange.

Will any 4.0L camshaft work in the '99 block?

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I can understand your reluctance to want to mess with the PCM. I was there once, too.

 

The first thing that an SCT handheld tuner will do once it's plugged into your OBDII port is download the stock firmware to its memory and save it there forever. If it's lost somehow, any tuner with access to the SCT tuning software will have your stock tune based on your PCM part number alone. If you ever want to go back to the factory tune, it takes about four button clicks, a few on/off cycles of the ignition switch and about 3 minutes of your time.

 

So, if you're not going to reflash the PCM to tune, how will you be compensating for the extra air you plan on pushing through this engine with a higher/longer lift cam and possible ported heads? Slightly larger injectors? Adjustable fuel pressure regulator? Keep in mind that larger injectors mean that you'll be squirting in more fuel throughout your RPM range. So, when you're at idle, your larger injectors will dump in more fuel. When you're cruising down the highway - more fuel. Wide open throttle - more fuel, but this is what we WANT to happen :) The stock OBDII PCMs are pretty smart, though. They can handle slightly larger injectors without needing a new tune. They'll use the injector duty cycle and the O2 readings to know that too much fuel is being dumped in and it will eventually correct itself to try and maintain a stoich. mixture at engine operating conditions such as idle and cruising. In my experience of slapping on larger injectors without doing the proper PCM tuning, I completely destroyed my city MPGs. My highway MPGs seemed to stay the same, though. Just something to think about...

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Holy Cow! That thing would make this truck a beast. But a little more than I want to do :rotf:

I can understand your reluctance to want to mess with the PCM. I was there once, too.

 

The first thing that an SCT handheld tuner will do once it's plugged into your OBDII port is download the stock firmware to its memory and save it there forever. If it's lost somehow, any tuner with access to the SCT tuning software will have your stock tune based on your PCM part number alone. If you ever want to go back to the factory tune, it takes about four button clicks, a few on/off cycles of the ignition switch and about 3 minutes of your time.

 

So, if you're not going to reflash the PCM to tune, how will you be compensating for the extra air you plan on pushing through this engine with a higher/longer lift cam and possible ported heads? Slightly larger injectors? Adjustable fuel pressure regulator? Keep in mind that larger injectors mean that you'll be squirting in more fuel throughout your RPM range. So, when you're at idle, your larger injectors will dump in more fuel. When you're cruising down the highway - more fuel. Wide open throttle - more fuel, but this is what we WANT to happen :) The stock OBDII PCMs are pretty smart, though. They can handle slightly larger injectors without needing a new tune. They'll use the injector duty cycle and the O2 readings to know that too much fuel is being dumped in and it will eventually correct itself to try and maintain a stoich. mixture at engine operating conditions such as idle and cruising. In my experience of slapping on larger injectors without doing the proper PCM tuning, I completely destroyed my city MPGs. My highway MPGs seemed to stay the same, though. Just something to think about...

Very good, insightful, thought provoking information here. From my understanding, the OBDII set up responds very well to an aggressive cam on an otherwise stock 4.0L. I would prefer to keep the injection system stock, but I know that may not be the case with a modified 4.0 and would upgrade to an adjustable regulator or injectors as necessary, once she is running. Perhaps at that time a tune may be necessary to maintain drive-ability. I spent many more hours this evening studying stroker builds and I am still not sold that a well built stroker can run on 87.

 

I did a lot of number crunching as well this evening. Here is what I came up with:

- Comp Cam 68-321-4 Camshaft

- Stock dished piston 0.030" over

- Block decked 0.010"

- 0.043" Compressed headgasket

 

In comparision to a stock 4.0L (numbers crunched by me)

Static Compression Ratio: 8.79:1

Dynamic Compression Ratio: 7.21:1

Quench: 0.0725"

 

The piston choice will still effect the compression ratios. Most aftermarket pistons have more dish volume, thus reducing the CR's.

 

Further thoughts and comments? Thanks :thumbsup:

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