Porting the stock LS1 throttle body--how to!

It's a simple way to get some extra ponies and if you already have the equipment it's super cheap. All you need is a dremel with some cutting bits, some sanding rolls, various grit sandpaper, and some Bondo or quick dry metal filler of some kind.

Here's the stock POS that we'll be working with. Our goal is to fill in that huge cut out area at the top, remove some material near the throttle blade and at the front lip of the body, and get us a true wide open throttle opening.

First off, you need to mark the throttle body at the blade with a marker so you don't be sure to go past the blade into the back side. Go too far and it'll cause all kinds of idle problems and weird chit. While you're at it, mark the shaft at each end where it goes into the body, like in the pic below. You can see both marks.

Now disassemble the entire thing. Remove all the connectors, unscrew and remove the blade, and remove the shaft. After you take off the tps, you can simply whack the shaft out with a hammer. Don't feel bad, it won't hurt anything. ***Pay attention as there is a very small washer that will fall out on the tps side too, do not lose this!!***

Now you need to fill in the cut out area that goes into the idle air bypass. I used 2 pieces of stanless tubing inserted before I filled it with Bondo. You can simply drill the holes later if you need to. I also put a piece of aluminum can against the opening and cut out 2 holes for the stainless tubes to slide through. This way the Bondo wouldn't completely fill the cut out area and choke it off.

While that's drying, go ahead and knife edge the throttle blade. I used a bench grinder, but you can use the dremel if you choose. Also, round the back edge of the blade off...airflow off the back is as important as the front.

Now move over to the shaft and get ready to cut it. What you will be doing is cutting off the front portion that you see when looking at the throttle body head on. When the blade is opened up this makes a big bump and a big restriction. Reference the marks you made before you took it apart and cut there.

Once the Bondo or your metal filler is dry, time to start porting. It will take a while, but be patient and be careful, making sure not to go too far into the throttle body (keep an eye on the mark where the blade will sit). Knife edge the leading edge of the body and grind back to your mark. Pay attention to the area near that mark, as there is a "lip" right there that is a major obstruction to air flow. You are able to feel it with your finger. Your rough cut should look something like this (if you didn't use the stainless tubes, that area will be solid filler):

Be sure not to go past your mark!!

Be careful on the porting, try not to take too much material away, the casting is quite thin in areas. Be careful on the bottom due to the coolant passageways as well. All that you need to do is continue smoothing and refining the shape, once you're done begin sanding it by hand with progressively finer grit paper to smooth the finish. I went down to an 800 grit paper and finished off with a polishing wheel on the dremel, then a little Turtle Wax Polishing Compound rubbed in by hand. Not the greatest finish on earth, but it looks good.

If you didn't use the stainless tubes, you will now need to drill some holes for air passageways. I believe a 1/4" or 5/16" drill bit will be sufficient, just make sure you check to see that you got the holes in their proper position. Remember from the stock cut out area that there is a divider smack in the middle of that area.

You will now need to do the bumpstop mod. If you didn't know, the stock bumpstop for the throttle cable USUALLY won't let the blade get to true wide open throttle. You need to clearance it to allow it to open further. There's 2 ways you can go about this, 1) with the tb installed and simply grinding till your voltage is correct or 2) with the tb off and install a set screw. I installed the set screw to add some adjustability. Either way, you want the voltage on the tps (the blue wire) to be at 4.7V at WOT, key on/engine off. Mine ended up at 4.74V, and I can adjust it either way. I *believe* the max voltage you can have is 4.75, but I'm not 100% sure on that.

Now, reinstall the shaft into the housing. For the spring, simply set one end into the perch on the side of the housing and slide the shaft through it. Once you get the tab that it sits on up to it, put the other spring end on it and twist it all the way around till the spring is tight then push the shaft the rest of the way on. Go ahead and put the throttle blade back on the shaft and make sure it functions properly, opening and closing. Shave the backside of the screws down and it should look something like this:

Clean the assembly with a mild cleaner (I used electrical parts cleaner) and reinstall. Attach all the fittings and hose going to the valvecover, and reinstall the electronics. Check your tps voltage to make sure it's correct. If you want, bypass the coolant that circulates through the body to keep the temps down. Simply put in a piece of tubing as a jumper between the 2 hoses and clamp them on. You don't have to worry about plugging off the fittings in the housing itself though. You can barely see it in this pic, but you get the idea:

Here is the finished product....expect a huge increase in throttle response and a great seat of the pants gain, especially up top. My auto also seemed to shift quicker and harder, but that could be just in my head.