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How to port and polish a throttle body

Porting and polishing a throttle body is a relatively easy mod that you can do yourself for free providing you have a rotary tool with some metal working attachments and some metal polish. The throttle body is usually the most restrictive part of any intake system, causing a bottle neck as the air rushes into the intake manifold on its way to the cylinders. By smoothing the transition down to the throttle blade and removing excess screw material, you can reduce the amount of turbulance that is normally created there. This helps smooth the airflow and help increase its velocity as it enters the motor. The benefits of this can be seen exponentially as the amount of air trying to enter the engine increases. So its easy to see how this can be a useful mod at any level. This mod should be relatively easy for anybody with some basic mechanical skills and some patience. I would rate it a three on a scale one to ten, ten being the hardest.

You'll only need a handful of tools to complete this mod. You'll need a 10mm wrench or deep socket to remove the three studs that hold the TB on. To do the porting you will need some sort of grinding tool, I used a Dremel type rotoray tool to do the entire job. A couple of different cutting or grinding wheels and a couple of sanding wheels will make the job easier. Some different grits of sandpaper or sanding wheels, starting at 80 or so and working down to 1000 grit would be good. Then just some alluminum polish and a rag. Some compressed air wil make the clean up easier but is not necessary just as long as you make sure that there isnt any metal shavings left to get into your motor when you're done.

Let's get started by removing the throttle body so that we can easily get to both sides and also to keep the metal shavings that we will be creating as far from the motor as possible. You will need to first remove the intake pipe connected to the to of the throttle body, this article will describe the process as done on a stock 2001 4.3l. The intake bonnet is easly removed by taking off the wing nut at the back and then tipping it forward to release the front clip. There are three 10mm nuts/studs that hold the throttle body to the intake manifold(fig 1). They need to be removed and then you can careful seperate the throttle body with out damaging the gasket/o-ring so that it can be reused.

The next step will be the actual porting process. This is easiest done using a carbide cutting bit on a flexible rotary tool. You will use the tool to create a smooth transition down to the throttle blade while removing the ridges that are left from the factory machining. These ridges are both on the topside and bottom side of the TB. You can see these ridges as they are circled in green in images 1 and 2. You will also want to remove the excess screw that holds the TB blade in(blue circles in image 2). These screws are longer than they need to be and will create turbulance and restrictions when the blade is in the fully open position. While doing all this, be very careful not to remove any material exactly where the TB blade seats in the closed postion. Creating any kind of gap around the blade will cause a number of starting and idling issues which will pretty much render the TB ruined. This critical area around the throttle blade is circled in red in image 3 and should be left alone. It might help to take a marker and make marks around the throttle blade in the closed postion so that it will be easier not to make any accidental cuts in this area.

Images 3 and 4 show what things should look like after the rough grinding is done. The shape should be smooth and even, polishing will not affect the shape so the shape needs to be perfect before proceeding to the polishing step. You can feel irregularities by simply running your finger around the throttle body. As a rule, if you can feel it with your finger it will affect the air as it passes thru. Takes some time and be sure that the shape is as smooth as you can get it again being careful not to remove any material around the closed throttle blade.

Once you're satisfied with the new shape that you have created its time to start the polishing. Start by using a rough sand paper around 80 grit. If you have a sanding attachment for the rotary tool it will make this step easier. When sanding, continue to stay clear of the area around the blade. You will want to repeat this sanding process while stepping down to finer and finer sand paper. The finer the paper you step down to, the more mirror like a finish you will achieve after polishing. Once you're satisfied with your sanding, you're ready for the polishing. You can use your choice of alluminum polishes. The polishing here can easily be done by hand with a soft cloth or microfiber. When polishing you will want to polish the entire bore of the TB including the area around the throttle blade that you havent touched yet. The polish should clean off any marker marks that you made earlier in the process. To finish things up make sure that you thoroughly clean the TB of all shavings by using compressed air.

Your finished product should look something like this, nice and smooth and ready to improve performance on whatever you put it back on. The noticiable difference you might feel will be in the throttle response and you will have at the least improved the most restrictive portion of your intake. Whats best is it was free, my favorite kind of mod.
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