Stock Throttle Body v.s. 63mm Throttle Body -
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post #1 of 2 Old 03-28-2012, 11:37 PM Thread Starter
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2004 WJ 
Join Date: Mar 2012
Location: Frederick
Posts: 137
Wj Stock Throttle Body v.s. 63mm Throttle Body

Being new to performance of the 4.0l motors, I would like to know if it would be worth upgrading my throttle body from stock to a 63mm throttle body. I know bolt on parts only do so much, and doing some research I have seen a back and forth battle between the stock throttle body design (necking down for velocity) and the bored out 63mm throttle body providing more volume.

I would like to know if anyone has done this upgrade, and what kind of results I may see.

Current Mods:
57 Series K&N FIPK
Magnaflow High Flow Cat
Magnaflow 2.5 in\out Muffler
2.5" tailpipe \3" tip

I'm not building a race car, but considering my WJ spends the majority of its time on the highway (daily driven) I'm just looking to get a little more pep out of it.

- 2004 Freedom Edition -I6\SelecTrac

There is a learning curve to everything.
BWYoung85 is offline  
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post #2 of 2 Old 03-28-2012, 11:56 PM
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2003 WJ 
Join Date: Apr 2008
Location: Tampa
Posts: 5,247
With hi flow parts on the intake and exhaust, the 63mm throttle body is the last bolt on piece of the puzzle. I'm guessing the exhaust manifold and pre cats are still stock, however? The more other mods you already have, the more you'll get out of each further upgrade. Your entire intake and exhaust system is essentially one continuous flow of air, and once you reach a significant bottleneck anywhere in that system, you're not going to see any further improvements until you change the bottleneck.

In this particular case, yes, you'll notice a little more pep and responsiveness with the 63mm throttle body. But your bottleneck is your cylinder head, exhaust manifold, and stock Y pipe with pre cats. Replace those pre cats with magnaflow high flow cats, pull off the manifolds, get a port and polish done on the intake and exhaust ports. Get a ceramic exhaust header, such as the Doug Thorley 635, and you've removed that whole section of bottleneck. That should net you a good 20 horsepower and torque, according to my high scientific and nearly sober conjecture.

One other word of caution. If your pre cats are deteriorating and losing their inner material, you can bet that it's all collecting up in your main cat and doing a nice job of clogging that one up. If that's gotten pretty bad, you likely won't see any difference just by putting on the throttle body.

I hope I'm still making sense. Any part you upgrade from the intake through the exhaust is going to have a potential power increase and an actual power increase. If you upgrade all of the associated parts, then you will be getting the full potential of each part. Upgrading one or a few things while leaving the rest alone isn't going to allow those upgrades you made to work anywhere near their full potential. I'll check this thread tomorrow and edit anything that doesn't make sense.

2003 WJ in Jeep Green Metallic, 4.0/242/4.10's. 4" Teraflex springs w/ RE monotube shocks and IRO short arms, cheap intake w/ amsoil filter, 2.5" hi flow cat and back exhaust, lots of lights and other misc crap.

Check out my build thread here:
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