Throttle body spacer - JeepForum.com
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post #1 of 10 Old 02-03-2017, 06:35 PM Thread Starter
96xjinprogress
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Throttle body spacer

Hey guys I don't know what kind of responses I'll get but I wanted to ask does anyone have a tb spacer on there 4.0 and do they help any. I just bought one from rough country and I'm undecided if I wanna put it on


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post #2 of 10 Old 02-04-2017, 10:47 AM
Tru2Chevy
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Originally Posted by 96xjinprogress View Post
Hey guys I don't know what kind of responses I'll get but I wanted to ask does anyone have a tb spacer on there 4.0 and do they help any. I just bought one from rough country and I'm undecided if I wanna put it on
Send it back, won't do a thing.

- Justin

1992 Cherokee Laredo - mostly stock, DD. 300k miles and counting

2004 Grand Cherokee Laredo - 4.7, bone stock - Wife's DD


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post #3 of 10 Old 02-04-2017, 01:40 PM
Timo_90xj
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Send it back, won't do a thing.

- Justin
^- this. You could just as well rig up a hairdryer into your intake and pretend it's a turbocharger.

Send it back. These are MPI- engines, so increasing throttle body length or volume won't do a thing to increase power or torque.

1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...


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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #4 of 10 Old 02-04-2017, 03:24 PM Thread Starter
96xjinprogress
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I see well thanks for the info guys. I was liking on the internet and I'd be better off just buying a bored tb


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post #5 of 10 Old 02-05-2017, 12:49 AM
Investinwaffles
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Yeah, they are useless

Bored throttle body, or some 4-hole injectors would be a much better investment
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post #6 of 10 Old 02-05-2017, 01:16 AM
Timo_90xj
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4-hole injectors won't really increase power either, but they can slightly smoothen idle and/or part throttle cruising.
The original 1-hole Siemens Deka injectors are far from perfect, but they actually work pretty well anyway. The stock injectors on ie. 5.9 ZJs are known to work up to 350+ horses. There's no real real reason to change them, but doesn't hurt either.

Money is best spent on upgrades that truly improve power/ torque.

1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...


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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #7 of 10 Old 02-05-2017, 02:25 PM Thread Starter
96xjinprogress
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Well timo I have a intake system on already and exhaust but I was either thinking on a header or some injector what would u recommend


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post #8 of 10 Old 02-06-2017, 06:07 AM
75SV1
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I'd probably look into 'upgrading' the exhaust first. Look at Charley's MPG thread or OK I'm blanking on the guys webpage in Australia. Also, the down pipe (cross over) seems to be the most restrictive.
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post #9 of 10 Old 02-06-2017, 07:01 AM
Timo_90xj
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Also, the down pipe (cross over) seems to be the most restrictive.
The downpipe dent doesn't really affect the flow rate at all. There's a nice test on Motor trend channel where they test bashing in the header primary tubes BADLY, trying to get the power/ torque down. Result can be seen from the youtube video.

https://youtu.be/azPKIjxmmdU


Power output drop is also pretty much non-existing even with the downpipe dent right after the collector on the 4.0 - what matters is you need a good header design, and you need enough diameter on the length of the exhaust, with a free-flow cat and a muffler that doesn't restrict.
I can't remember if it was Dirt everyday or whoever that tested different Jeep I6 4.0 upgrades on the dyno. Results were that most "junkyard bolt-on" upgrades resulted either in no power/ torque gains, or very minimal gains.


It really is about getting the basics right:
* Fuel injection and ignition systems in good condition
* Good intake - porting and port matching intake manifold, bored throttle body
* Ported cylinder head with larger valves
* Different cam for more lobe lift/ total valve lift, more aggressive cam profile
* High quality (roller) rockers that provide you with equal amount of valve lift, and possibly more valve lift over stock (different ratio)
* Good exhaust header, free-flow cat, free-flowing muffler, large enough exhaust diameter (forget about back pressure, even if it does increase low-end torque, overall power output will suffer with too small exhaust)
* Custom tune (Flyin' Ryan just quit supporting JTEC for Jeep/ Dodge, dunno if there are any other guys who can really do the job right on these)
*... list goes on
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1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...


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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #10 of 10 Old 02-06-2017, 08:15 AM
bluejunior
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To expand a little on Timo's basics: An important factor when trying to upgrade the 4.0 is that the factory intake setup is capable of providing more air than a stock XJ 4.0 uses at wide open throttle. So....any intake "upgrades" are almost completely pointless without complimentary changes further down the system. An improved header/manifold, clean/free-flow cat(s), 2.5" exhaust and a port job can allow it to use a smidge more air but even then you're not really looking at a huge change. Noticeable, but not even as big as a good cleaning and tune up will usually do for a new-to-you XJ. To really wake it up you need to do something that makes it demand more air like a bore and stroke, cam and valve job, forced induction, you get the idea.

I think a lot of the misconceptions about intake and exhaust mods are because there's a LOT of truck and SUV V8's and V6's (the old 5.0 explorers come to mind) that could make a lot more power than they did stock if you let them breathe easier. The 4.0, the later HO version with the better factory intake manifold in particular, is NOT one of these engines.
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Lifted, Locked, Stiffened

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