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More Power for 4.0?


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Just wondering what kind of quick jobs that could be done to get a little more pep out of the 4.0.

Specifically I was wondering if I were to get the injectors out of a H.O and swapped them in would that do something?- maybe paired up with a in-line fuel pump? I've opened up the exhaust and am gunna do intake soon.

Does anybody make performance intake manifolds for 4.0?

 

I don't really wanna get into cams or valves though 'cause its my DD and I don't wanna take it out of commision for more than a day.

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well yea you can get a k&n intake for it which does work. also look into installing a chip or investing in a power programmer. if you have a mechanic friend and your capalbe you might be able to do a cam in one day(undo wiring for engine on friday night) and pull the engine out on saturday morning and install new one by noon if you work for it and then allow some time for allinging the engine up with the tranny (its like the worst ever) and then hopefully done by saturday night!

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well yea you can get a k&n intake for it which does work. also look into installing a chip or investing in a power programmer. if you have a mechanic friend and your capalbe you might be able to do a cam in one day(undo wiring for engine on friday night) and pull the engine out on saturday morning and install new one by noon if you work for it and then allow some time for allinging the engine up with the tranny (its like the worst ever) and then hopefully done by saturday night!

 

haha, maybe if you work straight through the night friday and saturday night and finish up sunday morning. thats a pissload of work for two guys in one weekend. trust me, we did it minus cam-install we just swapped the motor

 

pulled the tranny+motor and bolted up the tranny to the new motor and put them both back in took friday saturday, sunday thru til 5am monday we fired her up

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What's this pulling the motor business? Take the rad out...

 

 

If you have A/C not realyl a good option. But I can pull a rad pretty quick, especially if it's on a vehicle I have owned for a while (and alreayd loosened all the fasteners and thrown away all the BS in the engine compartment).

 

 

 

Oh, power mods... Start with the not-so-power mods first. Gap all the spark plugs and check the ignition system for not being a pile. Check all the sensors and make the rest of the engine runs right (renix motors can need some TLC). Clean the TB. And perhaps even take the intake off and clean it and the ports in the head (mine were all coked up).

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Maybe. I think I want to try to get more revs out of mine. In first low the valves float really soon.

If the problem is valve float, look up the Mopar Performance Catalog on-line and order up a set of their dual-coil valve springs for the 4.0L. That should solve any valve float problems, and you don't even need to remove the head to change valve springs.

 

To be honest, though, I don't see why you want more RPM. The torque peak is at 2200 RPM or so, and I'm sure the valves don't flaot until over 5,000 RPM. By the time you float the valves, you're so far out of the power curve of the engine you might as well be on Mars.

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Like said above, make sure it is running in prime shape before you get more HP out of it.

 

But as far as boltons...:

 

- Hi flow Cat

- "Performance" Muffler (flowmaster, dynomax, etc.)

- Custom Air Tube

- Bored out TB

- Headers

- Larger exhaust pipes headers back (2.5")

 

Really not much to do under there as far as bolt ons go, but with the above, you should get maybe 20hp/25+lbs torque out of it, depending on your engines condition as is. No engine is alike in that sense.

 

Also, with those mods you will have raised the peak HP up a few hundred RPMs from stock, so you will have more top end grunt, like the HO motors. The renix motor definitely is all low end power, and thats it.

 

This is not intended to be 100% accurate, but I'm just trying to remember what I've gathered over the years :cheers:

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I put a Throttle body spacer in my YJ sometime back, It helped a little.

My 91 YJ has a 5spd and 2.5L 4cyclinder, with TBI.

Dropping in the throttle body spacer took me less then a hour, the spacer only cost me about $26.00

 

It did help.

It didn't give me TONS of extra Horse power or Torque, but I noticed that I wasn't downshifting as much on hills, and it gave me about 1/2 MPG boost on fuel efficency, (an investment that is still paying off!)

 

If you have a stick shift, these just "drop" right in between the throttlebody, and the manifold. If you have an Automatic, you'll need to adjust the shift linkage on the Throttlebody.

 

It's a simple upgrade, not sure how much it might help on the 4.0 litre, but it helped my 2.5

 

 

John

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wow lots of responses over the night, yah I've see the TB spacers before but there all like 60 bucks at the cheapest i've found, I dunno where you found one for 26 bucks. Also, anybody bored out a throttle body before? or do they sell oversive throttle bodies..... hmmm maybe I could jury rig a larger throttle body off of some newer junker V8

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I have seen aftermarket larger throttle bodies for the 4.0L, but I don't remember where. :( Rubicon Express I think.

 

Spacers aren't worth it on a 4.0 or other MPI setup. They "work" best on throttle body injection or carbs.

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How about injectors from the 4.0 HO, do they plug into the renix system ok? would they give any more power

 

 

Yeah, they plug in and work. They'll even flow more fuel. But, there won't be any 'real' gains. Apparently they have a slightly better spray pattern which might give you a tiny bit of power and milage increase. However, the stock injectors already flow enough fuel. This isn't a turbo-diesel where you get more power by just throwing more fuel at it.

 

If you're to do a few other mods (TB, intake, exhaust, port head, etc) then the HO injectors would probably be a good idea. Or even some larger stang injectors.

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Yes.
I wouldn't say yes for all injectors. I got a 98 XJ for parts that I'm installing just about everything into my MJ with, and found out I have a crap 98 injector harness. I went out searching for a new injector harness, luckily a dude on Naxja had one for 20 bucks with the injectors, and I was heading his way that weekend. I didn't think I'd need the injectors, but I grabbed them anyways for the whole $20 for everything, and when I got home, I compared to see if I could just swap the harness in. Nope. The connectors are slightly different and I didnt feel like making a hybrid harness. I still have the old injectors and harness, but I figure I'm probably better off with the 01 stuff then the 98. It plugged right into the ECU, so it *SHOULD* work.
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No clue on the gearing, 5 spd 2wd with P225/75.... It aint a wheeler yet, just my dd rig. Hopefully depending on what I do for school when I graduate next year I'll be able to throw some time and money into 4x4 convert and lift/tires. But for now its street only.

Back to topic- I'm really thinking of pulling the whole injection system and either refurbing it or put in a new rail, put in the H.O injectors etc, It also has a hell of a time starting so there could be some fuel restriction, I dunno, changed the filter but didn't change anything. Not to mention a new painted rail with braided fuel lines and race fittings etc. would look killer

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4.0L + stick = 3.07 gears. There's your problem. No need for expensive engine mods here. Go get a 3.55 geared rear axle (a dana 35 will work fine in this application) and drop it in. Your truck will come ALIVE with performance!!! I promise. :D

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I have seen aftermarket larger throttle bodies for the 4.0L, but I don't remember where. :( Rubicon Express I think.

 

Spacers aren't worth it on a 4.0 or other MPI setup. They "work" best on throttle body injection or carbs.

 

What gears are you running and what size tires?

 

X2 on both of Pete's comments above. Throttle body spacers had zero effect on my stroker. However the bored out throttle body definitely did, especially at WOT.

 

Besides the obvious power gains of a stroker engine, the most noticible performance improvement for me was regearing for the best RPM vs. tire size. An added bonus was a slightly higher RPM (200-250 RPM) vs. MPH over stock specs which put the engine in a more efficient power band and resulted in a 2-3 MPG improvement.

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