[Alex]

Well im sick of all these performance parts costing so much darn money...If youve got the metal, why not do it yourself? Here it goes...This write up is on how to bore out your throttle body.

This throttle body was bored out from i believe 58mm to 62mm which is comparable to the rubicon express throttle body...Link to RE Throttle body....Sure its anodized red and nice and pretty, and squeezes out an est. 15 more bolt on horsepower...But look at the price tag...$370.00 not including S&H. If you'd like, read on, spend a couple dollars on a grinding stone and a few hours out of your day.

Tools needed:

• Drill Press
  
• Any kind of degreaser
  
• Grinding stone for aluminum metal
  
• WD40 or any other lubricant
  
• Wirebrush
  
• 80-160 Grit Sand Paper
  
• Wirebrush
  
• Time and beer

Step 1:

Remove throttle body from intake manifold and save all hardware. If you can salvage your gasket, do it, otherwise you'll need to get another one from the autoparts store. Next, remove all TPS and IAC sensors. Clean the sensors and put them to the side. Degrease your throttle body with your favorite brand of degreaser so your working surface is clean and your grinding stone will not get gummed up with oil residues ect....


Step 2:

Measure out the inner diameter on the bottom of your throttle body...It should be somewhere around 58mm. From the remaining residue, there should be a little dark ring around the bottom of the throttle body which actually measure out to be about 62mm from outer ring to outer ring. With your measuring tape or whatever your using, make sure that your bore is going to be measured out to 62mm exactly and mark right around this ring. I used a razor blade and cut into the aluminum so i can make sure i do not go over the 62mm in the bore process.

Notice the dark ring around the hole. You can barely see where i made my ring on the aluminum. This is the boundry to how far i want to grind out of the throttle body.


Step 3:

Put your throttle body on your drill press and put on your grinding stone. Make sure your grinding stone is not touching the blade inside the throttle body. The last thing that you want to be doing is scarring this up. Next, put on a pair of gloves, spray the inner of the throttle body down with some lubricant like WD40 and kick on the drill press. Make sure that your RPMs are consistant while boring out the throttle body so some spots are not bored out deeper than others. Grab two opposite sides of the throttle body and move the throttle body around so the grinding stone is going around in a slow circle and making contact with the entire inner surface of the throttle bdoy. Each full circular movement should take you about 30 seconds or so. This is the part that will become exhausting and take you some time.



Periodically, you will have to spray down the throttle body with more lubricant to make sure your stone does not get too hot and the surface stay smooth and lubricated. You may also need to keep dumping out the metal shavings on the blade as they will tend to build up quickly. Make sure your throttle body stays clean throughout the entire process.



Step 4:

Once youv'e gotten your inner bore, out to 62 mm, you will need to adjust your working platform on your drill press to an angle of 20 degrees.



This is to create a smooth angled lip going into the intake manifold. This will help cure the "whistle" that is typically heard with 62mm throttle bodies that come from rubicon express, edge, and turbo city. This also helps increase airflow and gradually opens up into the intake manifold distribution chamber.



This process goes by very quickly so dont spend too much time grinding out the angle and in this process it isVITAL to make sure you spend and equal amount of time on the entire surface so this it is even.

Your final bore is going to look something like this:



Step 5:

In this step, you are going to be perfecting your the cleanliness of your bore job and clean up the metal to make sure it is smooth, allowing the air to have the least amount of restriction. This is comparable to mandrel bent exhaust tubing versus discount auto's weekly special on 90 degree ripple bends. In order to achieve a smooth bore, you will start by using something ike brakecleener to get out remaining lubricant and metal shards, and allow for again, a clean working surface. Then use a small wirebrush in a drill and on an angle, use it to smooth out where you just ground out the metal. This will smooth it out to where you can run your finger over it.

Next, use a 100 grit sand paper and move up to about a 150 grit pad to finish up the process of making the guts smooth.



Step 6:

Degrease your throttle body and clean all remaining metal scraps and dust off of the throttle body. At this point, you can either go ahead to bolt back on your sensors and bolt it back down to the intake manifold...or you can go ahead and take it a bit further. I went ahead and prepped the surface to allow it to be painted.

Here's the finished product


And sort of a preview on my new 4.7L stroker motor:


I will be doing a write up soon on the stroker motor. Get ready for the stroker motor swap because its loaded with just about every bolt on performance part you can get.

-Alex

PS, sorry for the long, over explanitory write up.

Any questions...please ask.

[Rollbar]

Very, very nice. Might I add on the final stage of sanding U might want to use a scotch pad also to even smooth down more.

Just a thought,
RollBar

P.S. I didn't know CJ's had throttle bodies.

[Alex]

Haha, good point about the scotch pad. I'll try that on the next TB i bore. Oh yes, i did forget to mention rollbar, before you start tearing your engine apart, this modification is good only for MPI vehicles.

Thanks for the heads up....

-alex

[Jim B]

Darn Alex,

Excellent write up and info for all, can't wait till you come back with the stroker.

[YJWhenUCanTJ]

Although I never confirmed it, I thought the aftermarket bored out TB's included a larger butterfly/throttle plate. My shadetree mechanic skills tell me that the boring of the area above the stock throttle plate will help to slightly speed up the incoming air by creating a venturi effect. But is there a comparison of power output on the web between a stock and bored TB where the throttle plate wasn't replaced? You did say it was a stroked motor so additional air intake ability is certainly a power adder, I'm just trying to find support that boring the area above the factory throttle plate will in fact improve power output. Porting and polishing the intake and exhaust runners and a 5 angle valve job would also help improve power output. Hey, if I had access to the tools in your pics, I'm sure I'd have bored out TB's on all my cars.

Hmm, after looking at the pics again, I finally noticed you were boring out the underside of the throttle plate. Now I'm really interested in the effect. That would seem to slow down the air moving past the throttle plate, hindering rather than helping air move through the throttle body. Am I way off base?

[Alex]

It's possible, although unecessary to bore above butterfly because the diameter is some where around 62 or 63 in diameter...The section restricting flow is the under part, which is what i bored. As for replacing with a larger butterfly, its un necessary unless you are boring over the entire thing to a diameter larger than the upper part of the TB, which would be anything above 62 or 63mm. The only restricting part of the throttle body is the underpart. If you pull off your existing tb, the underside is shaped in a odd way, allowing just enough room for the butterfly to open 100%. If this area is bored out, it makes the TB a straight shot, rather than a consistant bore diameter and then a lip thats about a 1/4 inch deep that is atleast 6mm smaller in diameter...around 56mm. If you eyeballed it, you'd know what im sayin. The angle that i put on the bottom finally allows the air to gradually open up in to the intake manifold chamber. This is also to eliminate the whistles typically heard at different throttle positions with your rubicon express intake manifold...Does it matter? not too much i dont think.

Finally the diameter of the hole into the intake manifold is i believe 68mm. Thats off the top of my head. These can be bored out to 68mm. I have seen one guy do it on another 4.7 medium-buck stroker. It was a flowmetrics tb which is a different design.



If im doin enough horsepower, i may see what i can do to open this one up more. I think i might have to. Along with this, i may have to port the manifold.

If im unclear...let me know...wish i was better at drawing diagrams in photoshop...I just tried, but i think i'd confuse u!

Anyways,

Alex

[YJWhenUCanTJ]

I think I'm able to see what you're talking about with the lip on the underside from the pics. My guess of the "odd shape" on the underside would be to assist in a smoother power band. Much research goes into the design of TB. Most passenger car TB's have what would appear to be less than perfect bores but actually serve to provide a smoother (not necessarily better) power band and efficiency at part throttle applications (like city and highway driving). I think what material you've removed may make the TB more responsive from the idle to full throttle application, but may affect part throttle driveability (which you may not even care about either). The shapes of the TB's air passages are of course designed for the average driver who wants smooth predictable power, not an all or none power band like a race car.

You'll just have to let us know your impressions of how the stroked motor drives in different situations compared to the stocker. You didn't give the I.D. of the intake manifold where the TB sits. Make sure the TB is no wider than the opening in the intake.

[Alex]

David you are exactly correct about the power band and throttle. Most people believe that the much quicker response when you put your foot down is the gain in horsepower and torque when in fact, as you pointed out, is actually how the air flows in relation to the shape of how that inner butterfly opens.

You also made a good point about intake manifold diameter and how it will flow from the TB into the chamber and making sure that it is just as wide or wider than the TB bore. This is why porting the manifold may be necessary on anything over 62MM as flowmetrics has said.

As for the ID number...do you mean the one in the cast? Im not too sure...If so, let me know that that is what you were referring to and i can get that number to you. Im planning on pulling the old motor sometime this week, and getting the new one in soon. I'd also like to take it down the street to the local dyno.

Keep you guys updated...

Once again,

Alex

[Frank YJ]

Nice Alex... so does this mean your still coming to Windrock in June?

[Alex]

Man, im workin my butt off in this florida heat trying to get everything together for windrock. I should have everything built by then. Headed over to roberts i think before the weekend to head out to L-cross. David allan coe!

Hows it goin up there in GA? Win anymore show-n-shines? Was plannin on givin you a holler to see what the deal was with some of these here trips we got planned.

Alex

P.S. Tell my nephew wrinkles what up, and eaaasy on them chickens!