I just installed a 4 liter throttle body with a TB spacer on my 2.5 liter along with new fuel injectors. I whouldnt have forked out the money for the TB spacer, but I got it for free so I threw it on. There was a huge difference my engine idles more smoothly at a lower RPM and the throttle is much more responsive! Comparing the 2.5 TB to the 4 liter TB, there was a huge comparison, allot more air can flow through the 4 liter TB.
Most results of these mods are heavily influenced by the well-known placebo effect. First, a throttle body spacer does absolutely nothing when installed under the type of throttle body used by the 2.5L and 4.0L engines. Nada, nothing. That type of throttle body passes nothing but air through it and installing a spacer only makes the air path longer.
Throttle body spacers can help when placed under older TBI (throttle body injection) throttle bodies but that's it. Spacers first became popular for carburetors where they helped there too.
Jp Magazine did a comparison test of a TJ with a 2.5L by installing a TB from a 4.0L and they said they noticed no improvement whatsoever. In fact, they said they might have even lost a little power from having converted to the 4.0L throttle body.
And the Jet chip, by law, can only do anything at wide-open-throttle and near redline rpms. You won't notice anything at all around town or on the trail with the Jet chip. It would only help a little if you were drag racing your Jeep.
__________________ When you have a choice, buy American.
Thanks for your response Jerry! I have read your other posts where you have shared your thoughts about the TB spacer, I too agree that it doesn't do much if anything. I wouldn't have forked out the money on the TB spacer or the 4 liter TB but I got them for free, so I decided to try them out... I too am a big believer in the the placebo effect and have to catch myself from not falling for it. IMHO I did notice a little smoother idling, however, that may have come from new fuel injectors and totally cleaning out the carbon build up from around the injectors...
Ive been contemplating on doing this mod myself and have been doing some heavy reading on it. I researched it, read it, and looked at other peoples dino graphs for this project. 4.0L throttle body alone will give you 8hp but you have to make sure you swap the sensors from the 2.5L throttle body to the 4.0L throttle body or else you will experience rough idling and wont get all that 8hp. The spacer alone will give you a wapping 4hp. Together they will give you 16hp. But.... this is a big BUT...If you do the throttle body with the sensors and take off your intake manifold and bore the intake manifold to match the size of the 4.0L throttle body and bore the helix bore throttlebody spacer to match the size of the 4.0L throttle body it will give you 25hp!!!!! This is all from what i read and dino graphs i looked at on other forums and from doing a bit of researching. I plan on going for the extra 25hp myself though.
You can find dynometer graphs to support whatever you want. Dynometers are not the precise machines some believe them to be. You can take the same engine and run it 6 different times on the same dyno and try as hard as you can to keep everything the same but you'll still get six different results.
Any chart that says a throttle body spacer gives 4hp is lying, it doesn't help, and most unbiased testers of the 2.5L notice no difference after installing the 4.0 throttle body. Jp Magazine said they felt they might have even lost a little power on their 2.5L after installing the 4.0 throttle body on it to test the rumors.
You are totally kidding yourself if you really believe all that is going to give you 1 hp, let alone 25 hp. Don't get suckered in by all the hype.
__________________ When you have a choice, buy American.
The TB spacer works on our Jeeps about as much as huge STP stickers on your doors will. In fact, the stickers may even give better performance.
Just to explain "Why."
The spacer's principle is to swirl the fuel/air mixture mist after the fuel has been added to the intake stream. The added length also gives it more time to mix - at higher speeds. At lower speeds it can even do the opposite, allowing the fuel to precipitate back to larger droplets. Some spacer mfgr's even tell you it creates a "ram" effect - or it lengthens the plenum chamber like a hi-rise manifold (carbs.) If it did, the spacer would need to be at least 3 feet thick!
They do work slightly on carbs and Throttle Bodies that inject the fuel in the TB - they atomize the fuel a little better.
But - our Jeeps don't have fuel up there in the TB, it's injected right at the intake valve. By the time the swirling air gets down the intake past the bends it's no longer swirling. Nothing is gained. It's the same thing with the "Tornado" insert in the air inlet - they do nothing.
Now think about it - the bigger bore of the 4.0 on a 2.5, or even a bigger bore on a 4.0 TB will let in more air - but of course only when it needs it. The only time the stock TB does any restricting is at very high speeds - maybe. They could help a little at Wide Open Throttle but it also needs more fuel. Larger injectors may help that - maybe.
If you really want to spend your money shop around for matched injectors. Using those insures that all cylinders are giving the same amount of fuel. You wont have some cylinders slightly rich and others slightly lean. The increase may be measurable on a drag strip, but you still won't feel it.
But even then, the psychological placebo effect gives the best performance - along with those stickers.
The most effective way to gain "seat of the pants feel" is gearing. Lower gears will cause the engine to run a little faster into the higher power curve. But - there goes mileage.
Through the years Jeep has done lots of small things to increase HP - a little at a time.
It's a Jeep, if you want a race car buy something else.
It's no wonder the country is falling apart - stupidity abounds!