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Unread 09-12-2001, 01:13 PM   #1
redneckwithajeep
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cheap 4.0 mods?

hey, everyone!
i have already removed the restrictor thingy (thats the technical term ) from my zj 4.0, and now im looking for more cheap things like this. who can help me?

thanx in advance

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Unread 09-15-2001, 02:13 AM   #2
Nightclaw
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Not too much in the way of completely free mods... A header comes to mind, as does an intake tube. K&N air filter, Random Technology catalytic converter, Magnaflow muffler...

None of the above are especially pricey, but none are "free" or of "insignificant" expense. Total for the above would run about $600 out the door - which is inexpensive to me, but may be excessive to others. YMMV.
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Unread 09-15-2001, 03:26 AM   #3
EricsXJ
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Mr. Redneck,

Share the wealth man! What is this restrictor thingy you speak of and did it make a difference?

As far as cheap, or free engine mods, I've heard of people cutting holes in their factory airbox and other stuff to get better air flow. However, I DO NOT know if this works or is even a good idea to begin with.

Anyone else?
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Unread 09-15-2001, 07:20 AM   #4
HighCountry
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I am not sure which years this applies to, mine is a 1995 model.

There is a small metal plate bolted directly in front of the airbox inlet. Remove it and you get fresh COOL air from in front of the radiator.

The inlet hole in the airbox is tiny. I suggest enlarging it to approximately the size of the above mentioned metal plate. ?Don't over-do it or you will weaken the airbox.

There is an "orifice" type arrangement in the airbox where the rubber pipe going to the throttle attaches. This is to cause a vacuum pulling the fumes from the charcoal canister which the fuel tank vents through. I removed this orifice, giving less restriction to the engine breathing.

The exhaust pipe from the the manifold-header on some years is much smaller than on other years. I purchased a new stock exhaust pipe from an 1996 model, then a nice large straight section of pipe to connect it to my new low restriction muffler and finished it off with a stock tailpipe of 2.5 inches from an 1989 model.

These few things made a HUGE difference in how the Jeep performs from 3500RPM on up to redline, and improved the fuel economy about 2MPG.
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Unread 09-17-2001, 08:23 AM   #5
bonehead99
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A cheap mod is to remove the factory airbox and replace it with a K&N cone filter. I used a peice of thin wall pipe (free have connection) and some aircleaner hose (couple dollars) and a K&N I think 67mm cone filter ($30 on ebay). I could really feel more lowend takeoff power. I mounted it to the support brace for the front grille. It is now slightly above the top of the engine. Make sure to hookup all hoses back to the pipe or aircleaner hose.
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Unread 09-19-2001, 01:37 AM   #6
redneckwithajeep
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Tanuki, the restrictor thingy is easy to get to. take off the hosr from the throttle body to the airbox. at the airbox, where the hose connects to, you should see a white (or black) insert. this removes with just a screwdriver and pliers. BOOM!, 10 more HP.

P.S. thanx for the help, High Country!
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Unread 09-19-2001, 08:53 AM   #7
bcompton
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K&N cone filters do add airflow and therefore power, BUT, if you remove the factory airbox, you are also giving up a built in water trap that prevents hydrolocking in all but extreme situations.

Think about it, the factory box (at least on my 01 TJ 4.0) lets air in, and the filter and engine tube pull from the top. There are drain holes in the bottom. So,water would collect below the filter and drain out before being sucked into the engine.

With the K&N setup, there is no trap for water, so any water that hits the filter gets pulled directly into the engine.

Just something to think about....
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Unread 05-16-2009, 06:38 PM   #8
jeepinirishman
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Does the restrictor thing work on 03 wrangler
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Unread 05-16-2009, 11:24 PM   #9
StellaTheZJ
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Has anyone actually dynoed the HP increase from removing this restrictor? I understand the principle (bigger hole=more airflow), but there's another side to this story.

Whenever air has to enter a hole with a sharp edge, there is a "virtual restriction." As the air coming from anywhere but straight in front enters the hole, it has to move sideways first, and then turn into the hole. Unfortunately, it can't turn 90 degrees, so the air entering from anywhere but straight in front ends up piling up in the middle of the hole. A simple 3" diameter pipe with a sharp, square-cut end will not flow as well as a 2.5" pipe with a 1/2 radius on the entry! Check out the K&N test procedures, and all of their testing is done using mounting plates with a ".250 radius" installed. http://www.knfilters.com/testmethod.htm

If this sounds hard to believe, there's a cool way to test this. Fire up a vacuum cleaner, point the hose up (so you can look into it), and shake a bunch of flour or sawdust into the air above the end of the vacuum hose. You can clearly see all the flour flowing into the middle 2/3s of the vacuum hose, and the region around the sides of the pipe stays clear! So, you can clearly see the virtual restriction of a pipe with a sharp entry.

The reason I bring this up is because the "restrictor" has a beautiful, radiussed entry to it. The airbox, with the restrictor removed, has sharp edges. The gentle radius of the restrictor greatly helps airflow, even though the smaller venturi just behind IS a restriction.

So, has anyone dynoed this mod? Which wins, bigger hole, or smoother entry? By the way, science be damned, I did this the first day I had my ZJ!!
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Unread 05-16-2009, 11:26 PM   #10
StellaTheZJ
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Wasn't there a magazine article on this??

(googling... googling... googling Will Robinson...)
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Unread 05-16-2009, 11:29 PM   #11
TMar
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Nerco!

10
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Unread 06-09-2009, 05:20 PM   #12
StellaTheZJ
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Bump... and what's Nerco 10? Googling it did not produce definitions that make sense in context...
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Unread 06-09-2009, 05:24 PM   #13
iananderson17
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I think it was supposed to be necro, cause the thread was brought back from the dead...8 years ago, dead. and the 10 is just because you need at least 10 characters to be able to make a post.
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This has got to be the first thread where a free gear upgrade was done. At the start, the OP had 3.07 gears, now he has 4.10 gears. And it didn't cost him a dime.
Show that to your dad !!
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Unread 06-09-2009, 05:33 PM   #14
jgorm
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Quote:
Originally Posted by StellaTheZJ View Post
Has anyone actually dynoed the HP increase from removing this restrictor?
give me a couple months to setup my shop and i'll dyno test all the free mods! (ill be sure to post them up)
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Unread 10-23-2013, 10:16 PM   #15
Basaku
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Quote:
Originally Posted by bcompton View Post
K&N cone filters do add airflow and therefore power, BUT, if you remove the factory airbox, you are also giving up a built in water trap that prevents hydrolocking in all but extreme situations.

Think about it, the factory box (at least on my 01 TJ 4.0) lets air in, and the filter and engine tube pull from the top. There are drain holes in the bottom. So,water would collect below the filter and drain out before being sucked into the engine.

With the K&N setup, there is no trap for water, so any water that hits the filter gets pulled directly into the engine.

Just something to think about....
Speaking of cheap proformance stuff, as long as you don't submerge your intake filter i strech panyhose over the intake filter, you can also do this with the stock boxes... Hahhaaha funny but.. You can shoot a garden hose at my intake and minimal water gets in side... Even helped with trekking into deeper water with that wave of water you make.
I dont suggest going and buying them your self ... Tons of wierd looks all the way back to your car =)
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