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post #1 of (permalink) Old 02-26-2003, 10:27 AM Thread Starter
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Throttle Body

Everyone want more power, and I have heard af people getting a little bit more power out of there 4.0 by geting a new throttle body. My friend has one from turbo city, and was very pleased with its results he thinks that he gined more power without losing low end. So I got to looking at it and it looks like the only difference is that the bore below the butterfly is larger than before. So I took mine off yesterday and looked at it and the bore above the butterfly is about 2 6/16" and be low the plate is 2 3/16". The intake manifold hole is 2 7/16". Anyways, I really dont want to pay $200 for one if I could do it myself. Any ideas? Is there even any power to gain, do you lose power?
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post #2 of (permalink) Old 02-26-2003, 01:28 PM
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Re: Throttle Body

yes you could fo this as long as the butterfly valve still operates properly. you will need access to a machine shop though since doing it my hand would prolly mess something up. machinists are expensive if you cant do it be warned.

you could maybe get a 4.0l throttle body from a junk yard so you can work on the TB and still be able to drive around. i've seen em about 75$ at yards.

good luck and let us know how it goes and the results on your engine
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post #3 of (permalink) Old 02-26-2003, 01:45 PM
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Re: Throttle Body

check out this web site. Looks like a good mod.

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post #4 of (permalink) Old 02-27-2003, 06:45 AM Thread Starter
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Re: Throttle Body

Well, I went down to a machine shop that has done work for me before and he said he would bore it out, thin the bar down that holds the butterfly (which will give even more airflow, especially at full throttle), and give it a good cleaning, all for $60. So I unbolted it, and he has it now. When I get it back Ill post about the gains.
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post #5 of (permalink) Old 02-27-2003, 09:53 AM
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Re: Throttle Body

Spacing it up a bit also adds mid to high end power.
It increases the plenum area underneath, taking some of the
pulsations out and giving a fuller "charge" in the cylinders.

Generally spacers are only 1-1.5" thick because of hood
restrictions and fuel line issues. Some spacers have ridges
inside to create turbulence to help keep it mixed, but I'm
not convinced that turbulence doesn't create hi-end airflow
problems as well.
Usually "smooth" is the word for induction systems.

Check Summit or Jegs for TB spacers, something may be
available for yours.
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post #6 of (permalink) Old 02-27-2003, 10:13 AM Thread Starter
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Re: Throttle Body

Yeah I was thinking of getting one of those next, but like you said most of them have swirls in there to create a tornado effect and I just think the swirls would be more obtructions to my air flow. But I cant wait to get my TB back on. I pick it up at 4:30 today so we will see what it does. Should I unhook the battery for awhile so the computer will reset and then adapt to the new air flow for air/fuel ratio?
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post #7 of (permalink) Old 02-27-2003, 11:45 AM
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Re: Throttle Body

I rather doubt the computer will care, but you can.
Really the only time the airflow is increased with the larger
bore is at Wide Open Throttle. The rest of the time the
butterfly's closed enough to limit the airflow to it's

Someday when I get a chance I want to make dyno comparisons
with the spacers, smooth vs the spiral bores. More than
likely the spiral types give a better atomization at mid
range, and may inhibit top end a bit, but if it's big enough
it won't matter that much.
And - it depends on where you want the added "poop."

Matching the TB bore to the manifold bore probably will be
the biggest improvement in yours, since you said the difference
is a 1/4" mismatch. That makes a ledge causing turbulence.
But then, who knows, maybe that mismatch turbulence was
intentional by the designers.

Another improvement is matching the flow rates of the injectors.
Straight out of the box they are often mismatched, causing one
side to be leaner than the other. The computer "averages"
the two, leaving some cylinders slightly lean while others
are slightly rich - neither side is at peak performance
that way.
Depending on the engine and how far off they are, significant
improvements can be made by matching them.

Do a search on the internet for matching services, or call
your local speed shops, they should know someone that does
it locally. It's not all that expensive, as they do it on
an exchange basis.

Let us know how it comes out with the larger bore.
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post #8 of (permalink) Old 02-28-2003, 05:23 AM
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Re: Throttle Body

The machining shop where I am doing the coilover conversion and really top notch [img]images/graemlins/RockOn.gif[/img]
What if I wanted to make my own TB spacer? .. any suggestions?..advice?
BTW..I have the 4.0 L engine
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