How To: Porting and halfshafting your stock throttle body

[cgrant26]

This write-up is intended to be very n00b friendly so there will undoubtably be steps or instructions that seem like plain common sense. Feel free to skip through parts that you don't need. Also, this write-up is geared to the 94-98 Stangs, but most of it applies to 99-04 Stangs as well.

First, make sure you have all the tools you'll need before you start. nothing sucks more than having to stop in the middle of a project to get
something you need. It sucks even more if the car your working on is your only means of transportation. For the 94-98 V6 Stangs you'll need the following:

TOOLS:

3/8" drive Ratchet
2" socket extension
5/16" deep well socket and/or wrench
10mm socket and/or wrench
1/2" (or 13mm) deep well socket and/or wrench
Philips head screwdriver
Awl or similar sharp item
Dremel tool or die grinder
Cut-off wheel(s)

(If porting)
Grind stones and/or cutting burrs
2 1/2" Flap wheel sander
Die grinder or hand drill
Sanding drums

Supplies

Lock-tite or other thread locking compound
Anti-seize
Replacement TB gasket (optional)
can of brake parts cleaner
Tapered head screws for the butterfly plate (optional)

These are the grinding/sanding bits that I had on hand. You will probably not need all this but it's nice to have it and can make the job much easier and faster. For tools, I have a Dremel with Flex attachment, hand drill and a pneumatic die-grinder, but you could probably get away with just a Dremel.

[cgrant26]

OK now that we have all the tools and supplies covered, lets get started.

THROTTLE BODY REMOVAL:
(If you already know how to remove your throttlebody, you can skip this portion.)

First you will need to remove the induction tube. To do this, simply loosen up the 2 hose clamps that attach the induction tube to the TB and MAF/Air Filter canister) Next, unplug sensor plug wire and pull out the PCV vacuum line.



With the induction tube out of the way, you can now access all the parts off the TB you will need to remove it. First, disconnect the throttle cable, cruise control linkage and return spring.



Then disconnect the plugs on the IAC (Idle Air Control) and TPS. (Throttle Position Sensor) Now remove the 10mm bracket nut on the top left of the TB. Bend the bracket out of the way and with a 1/2" deep well, (or 13mm deep well)



then remove the 3 nuts and one stud holding the TB to the upper intake.

[cgrant26]

PORTING AND HALF-SHAFTING

Now that you have the TB removed, you can begin doing the fun stuff. First off, you'll need to mark the cutting points on the shaft. With the butterfly plate still installed, take an awl or other sharp item and scribe the FRONT SIDE (side with the screw heads) of the shaft at the edges of the bore.



Make sure your marks are deep enough to see with the shaft out. Once your marks are made, unscrew the 2 philips head screws holding the butterfly in place. (Noting the orientation of the plate) Open the throttle all the way and slide the plate out of the shaft. (Note: the plate only comes out from the front opening of the TB) Now you can remove the IAC and TPS. The IAC requires either a 5/16" deep well socket or wrench and the TPS is held in place with 2 philips head screws.



Once they are removed, you can extract the TB shaft. Simply pull it out of the TB by the throttle linkage. (Note: you may need to clean deposits off the shaft to remove it) Once out, locate your marks and if necessary/desired, highlight them with a sharpie. Double check to make sure the front of the shaft is what your about to cut, it will be the side with the screw recesses and no threads in the holes. Secure the shaft by what ever means you prefer and cut the shaft to the inside of your marks with your cutting wheel. I held mine by hand when I cut it.



Now that you've half-shafted your TB, you can install it as is, or you can make some further improvements. If your going for the maximum improvement, you'll need to get some tapered head screws to replace the existing butterfly plate screws.

[cgrant26]

Recessing the screws
This is probably the most difficult part of the entire process. The original screws offer a small degree of adjustment to get the plate alignment right but the taperd screws will lock the plate in place so getting the tapered holes right is critical to the proper function of your TB.
You will need to taper the screw holes on the butterfly so that the new screws can recess into the plate. The plate is made of brass and is pretty easy to cut so your best bet here is going to be using a grind stone with the same taper or close to the taper of the new screws. This is pretty much a process of trial and error. You will need to remove a bit of material at a time and then test fit the plate to the shaft while it's mounted to the TB. Each time you do this, check the alignment of the plate so that it opens and closes without binding up. When I did this one, I shaved the holes with a razer blade until everything fit right. I probably had to install the plate and shaft a dozen times before getting it where I wanted. (Note: Make sure you only taper the side with the stamped writing on it)



Knife edging the plate

Another thing you can do is to knife edge the plate. This involves simply chamfering the front leading edge of the butterfly. This is very simple to do and probably the quickest step of the whole process. Of course, you must be careful as chamfering it in too far will cause the plate to not close fully against the TB wall which will result in your engine idling poorly.
For this part, you can use a razer blade, any grind stone or a strait file.
The image below shows a nice conservatively done edge.
(Note: The butterfly plate's leading and trailing edges are not cut perpindicular to the plate face from the factory)



Knife edging the shaft

Once you have your plate finished the way you want, mount it to the shaft with the screws your going to use. Then lay the shaft with the plate face down and get ready for more grinding. Again, there are lots of ways to do this, but I found what works best for me is using the cutoff wheel at a very sharp angle to "shave" the shaft down. While doing this, you will also shave the screw ends down to match the shaft. On this one, I went down to about 0.150" shaft thickness. You could probably go even thinner if you are a bit braver than me.
(Note: keep track of which screw was in which hole)



Strait-on shot of finished shaft and plate:

[cgrant26]

Porting the TB inner bore
In this part, you will smooth down the ledge inside the TB and gasket match the back side. (NOTE: If you gasket match, be sure to do the same to your upper intake) To start, choose a good tapered grind stone, cutting burr or sanding drum and focus on grinding the ledge into a smooth transition from the middle diameter to the front diameter. It is VERY important that you don't touch the actual seating surface where the butterfly closes against the inner bore. Opening the contact are will cause the car to idle improperly and can only be fixed with a new, larger butterfly plate.



The next part to porting the inner bore is gasket matching and boring out the front and back parts of the TB. Again, unless you plan on replacing the brass butterfly plate with a larger one, stay away from the edges where the plate makes contact. For this part, you can use pretty much any type of rotary sanding/cutting/grinding bit. When I did it, I used a flap wheel sander which kept the inner bore perfectly round and produced a nice smooth finish, however, it took a long time doing it that way.
(Note: The rear ledge doesn't need as much attention as the front as it will not be a flow obstruction)
Also, a quick tip: If your using a hand drill + flap wheel to polish the TB, you can keep from hitting the plate contact surface by laying the TB on the ground and placing a 1/2" socket inside the TB. This will act as a stop to keep the flap-wheel from going too far in.

[ZStang]

Nice...I like a write-up that spares no details. Great pics btw.

[taylor0987]

where do you find those 2.5 inch flap wheels? I can only find dremel size ones or 3 inchers. I have looked at Home Depot, Lowes, and Harbor Freight.

[cgrant26]

I modified mine from a 3" wheel. Just cut the individual flaps down. It's a bit of a PITA, but worth it IMO.
If you look at the first pic, you'll see where I cut a few flaps uneven with the rest.
Also, the smaller 2" wheel in that pic with the material between the flaps was purchased from Granger. It doesn't abrade for shit, but is does a decent polishing job.