4 banger throttle body spacer?

[thechief86]

Hey guys, I am about to pick up my new DD, which is a 97 Tj with a 2.5.
I have been spoiled to 4.0's in all but one of my xj's, so I know that thing is going to be a total slug.
I had read that you can put a 4.0 throttle body, and a spacer on the 2.5, and grind out the intake to match the bigger throttle body, and use the ford 19#
Injectors to get a little more out of it powerwise.
I've also mostly read that throttle body spacers are a joke, and are about as effective as a 3" body lift. Which opinion is right? I just want to be able to drive the Tj on the highway with 31's and the stock 4.10's. nothing fancy....
EDIT: BTW, I know it isn't an Xj, but the same physics would apply, since it is the same 2.5 that many xj's came with. No need to ban me from Naxja or anything. It's just that in my experience the average Tj owner will put 37's on a 4 cylinder with a Dana 35 and rock that motha. Not me.

 

[sidriptide]

i've played the 4banger games... it's really money wasted. i assume its a 5spd but there are autos out there.
if you run 31s you will be lower in the power band than you want to be but you'll be fine around town. the highway will require foot-on-the-floor and you shouldn't hope for more than 65 or 70 unless you are drafting 6 feet behind a semi... and YES that really works.
i enjoyed both a YJ and TJ in 2.5L flavor, TJ was on 235s and YJ on 31s. both were ok for highway, just not "great". but the fuel economy was rock solid at 19 regardless of city of highway.
get the 4 banger and enjoy it. accept it's limitations and get used to WOT driving.

 

[O-Gauge Steamer]

A TB spacer is marketing hype and serves no purpose except to separate you from your money. More important would be to first identify if the intake is restricted, choked down so to speak.

There is a very simple test that you can run that will identify any choke points in the intake track.

The test uses a vacuum gauge which can be purchased for very little money, Plug the gauge into the intake manifold and run the engine to WOT. This is done in the driveway, do not need to be on the road.

If the gauge reads 5"Hg or less at WOT, do not do anything as there will not be any performance gains made.

At WOT, the manifold should "drop" (it actually rises...) to ambient atmospheric pressure. So, the vacuum gauge, ideally, would read 0"Hg.

If the reading is above 5"Hg, then the culprit must be found. Disconnect the TB from the air tube going to the stock air box (assuming you still have one) and rerun the test. If the gauge now reads under 5"Hg, then the filter is the issue.

If, and it is unlikely on a stock engine, the gauge still reads above 5"Hg with an open TB, the TB is a choke point.

Not to long ago, I ran this test on my rig and found that the TB had to be replaced. In my case, it required a 68mm TB to resolve the choke point. My Jeep is Supercharged and that is why the large TB.

I have used this test for decades across many displacement engines. The principle is the same regardless of displacement as so are the results.

 

[thechief86]

That's pretty neat! I'll give that a shot when I get home with the jeep. I just figured it would make a better DD than my lifted Xj with a front locker, welded rear axle, And some 33's. The Tj has 235's on it now, but I have some 31" dueler revo2's that I'd like to put on it. I will only need to be able to drive the 4 bangler about 10 miles each day, in town, so I imagine it will be ok. For long road trips I have my wife's little hatchback deal, or a freightliner big rig. No need to flog the wrangler trying to maintain highway speeds, but wondered if it would do it...

 

[thechief86]

Update: today I drove the Tj about 20 miles on the interstate, and got it up to about 80, with the top down. It didn't really seem to have as much trouble maintaining that speed on 235's as I thought. Actually, it holds 80 better than my 73 Vw does, but that thing only has 60 hp and only 4 gears, lol

 

[O-Gauge Steamer]

I had a 1948 CJ-2a that, new, was a whopping 60Hp. It was far from new. What it did have going for it was the 5.38:1 gears sets. Would pull and climb like nobodies business. Unfortunately, due to the low gears, it topped out at maybe 60mph. if you dropped it out of an airplane...

This is how a lack of Hp is compensated. Run lower gears to make torque at the axle. Really Old School. You might be amazed at just how low everything was geared back before high Hp engines became the norm.

 

[thechief86]

Yeah, I know a little about that. My 84 Xj pioneer had 4.56 gears from the factory with the 4 cylinder and ax5. Some kind of tow package or something. Once I put 32's on it, it was actually still peppy and I could do 70-80 on the highway.

Monday night I drove the Tj 200 miles home, on 235's, towing a 69 Vw beetle. Boy did that suck! 10-12 mpg, and I could only get up to 65 if the big rig I was drafting went down a big hill, lol. Today I put my 31's on it, and it seemed ok, even on the highway with hills. That is, until something went wrong with my driver rear brake starting to drag. I friggin hate drum brakes. As you can imagine, It was really slow then, lol.

 

[thechief86]

Well, I tried to help my power by installing some injectors from a '91 mustang gt, and it runs like crap now, lol. I thought that 19# injectors were supposed to be an upgrade (read that on a wrangler forum, turns out they meant yj's).
So I read around some more, and one thread says the tj's got 24# injectors from the factory, so I guess that's the screw up? Jeep will barely run when cold, then once warmed up runs ok up to 3500 rpm, or if the pedal is pushed to WOT, then it more or less dies until I let off the gas. I guess I'll put my old injectors back in for now, lol. Anybody got any other suggestions?
With stock injectors 5th gear is more or less useless.