HOW TO: Modify a Stock Throttle Body (FastMan Style)

[welby]

Hey everyone, I've had a few people ask me how I went about modifying my stock throttle body so I decided to do a how to on it.

If this is your first time doing something like this it's really pretty simple so relax. I've done a few of these types of projects ranging from TB's to cylinder heads and it's fun, but time consuming.

What you need:
-Throttle Body assembly
-Dremel Rotary style tool or Die Grinder
-drum sanding attachments, flap wheels, finish-abrasive buff, polishing wheels/cones, polishing compound.
-compressed air and/or a shop-vac
-TB cleaner
-optional: dial caliper to keep track of your progress (really not needed)

I picked up a spare TB from a local salvage yard for $70. I started out removing the TPS and the AIS motor that came with the unit. Now would be a good time to mark the Throttle shaft where it comes through the body and into the throttle port. This is going to be used later when cutting the shaft.

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Remove the two torx screws that hold the blade in place. Open the the throttle and pull/push the blade out and set it aside. Now you have to remove the snap-ring that holds the throttle shaft in place. It's where you just removed the TPS from. Snap ring pliers are nice here, I'm used to using automotive picks by now (they're magnetized, so it's nice to have that peace of mind, just in case you slip)

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Now you can remove the throttle shaft assembley, along with the return-spring.

Looking at the bare throttle body you can see that it chokes down just inside the opening, then opens back up just before the blade. The idea here is to open this all up, within reason. You can go as far as you want, but DO NOT remove any material where the blade sits.

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I placed the body in a vice and used a Dremel with drum sanding attachments to remove most of the material. Before doing so I packed the shaft bearings with grease, so as to not get shavings/dust in them. I started with 60 grit and went to 120 grit. Some people will use a die-grinder, but I don't really feel that it's necessary. The aluminum is so soft that you don't really need much torque. When grinding I usually have a shop-vac running next to my work, to keep the aluminum dust out of the air.

GO SLOW. Just take your time and work the port open little by little. After I was done with the 120 grit, I went to flap wheel and then to a finish-abrasive buff, and finally to a polishing cone with some polishing compound/sealer.

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As you can see I left a slight bevel at the bottom of the port, just before the blade, hoping to keep some low speed port velocity.

For the throttle shaft, I used a hack saw and very slowly and carefully cut the shaft, half way through, at my marks. Be carefull not to bend the throttle shaft when you're cutting it. Test fit it with the blade in place and the screws in it. Trim it if necessary.

The blade is a little more tricky. You really don't have to do this part of it. I did because I had the tools to do it and have done it before.

I placed a piece of tape over the holes in the blade. Then, using a properly sized suction cup (can be found at body repair shops, and cups for valve lapping are normally too small), I worked the blade on a belt sander with a very fine belt. I did very little to this blade, just really touched it up and smoothed it out. It started out at around 63 thousandths and ended up around 53 thousandths.

Now, clean the TB good with cleaner and compressed air. Remove the grease from the bearings and then lightly re-grease them. Re-assemble the rest of the TB (don't forget the snap-ring), and install it.

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I hope I didn't forget anything, and I'm sorry I didn't have more pictures. Please ask questions or give extra information if you have it.

 

[SavageUrge]

Great write-up! Thanks again!

 

[MoladoGuy]

Thanks Welby! This may be an upcoming project for myself. Do you know if that junkyard had any more TB's? It's the JY on Joy Road next to Selfridge right? I'm down that way sometimes at a friends home.

Again, awesome write up!

 

[Atrus]

I think Ernie's is still over there right near Selfridge. The big one used to be called Shaw Bros (the one just down from the Traffic Light), but I am not sure of the name now. I know it changed. There's also G & T on Gratiot and 22 mile.

I used to frequent the junk yards for prior cars

 

[MoladoGuy]

I think Ernie's is still over there right near Selfridge. The big one used to be called Shaw Bros (the one just down from the Traffic Light), but I am not sure of the name now. I know it changed. There's also G & T on Gratiot and 22 mile.

I used to frequent the junk yards for prior cars

There is also a line of them on Groesbeck between 10 and 12 mile road. I usually go to Macomb Auto Salvage on Bunert near Macomb Community College.

 

[welby]

It's still Ernies I think, I didn't really pay attention. I've gotten things from there before, so I just stopped in on my way home. I don't know if they have any more currently. I usually try to got to the u-picks, mainly Warhoops (lotta cool stuff here).

 

[tjkoen01]

What is the purpose behind putting the cuts in the shaft?

 

[welby]

What is the purpose behind putting the cuts in the shaft?

Simply put, for better flow/less obstruction of flow

The shaft is a cylinder with a notch in it that the throttle plate slides into. So you have half of a cylinder on either side of the plate. You cut it to remove the front half of the shaft, leaving just the back portion of it (the part with the threaded holes, the front holes aren't threaded).

I can dismantle my stock TB later on and get more pics if you'd like. Thanks for the question.

-Marc

 

[MoladoGuy]

Simply put, for better flow/less obstruction of flow

The shaft is a cylinder with a notch in it that the throttle plate slides into. So you have half of a cylinder on either side of the plate. You cut it to remove the front half of the shaft, leaving just the back portion of it (the part with the threaded holes, the front holes aren't threaded).

I can dismantle my stock TB later on and get more pics if you'd like. Thanks for the question.

-Marc

If you could do that without it being a problem that would be great!! I plan on doing this as an upcoming project and getting more involved with my soon to be father-in-law. He's a retired mechanic and he loves doing stuff with the Jeep cause it gets his hands dirty again. LOL.

 

[welby]

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There's a shot of the removed throttle shaft. You can see where the plate slides into the middle of it. On top you can see where the two T20 torx screws set into it, and on the bottom are the threaded holes for them.

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[Atrus]

I'd like to throw out a word of caution - I'd take extra precautions to ensure the throttle-plate retaining screws are not going to come out. I'd either smash a few threads on them to make a poor-man's locking fastener or use some heavy-duty threadlocker.

Sorry about always bringing up the Grand Prix, but it's the majority of my automotive experience....people were porting the TB's for the GM 3.8L's, and in the beginning there were issues with the screws coming loose. Bad enough on a naturally aspirated engine, but the L67 (GTP) version uses a roots blower. That really cost a lot of people a lot of money when the backed out and got sucked into the intake!

Another work of caution....not sure how the KJ TB's are, but I attemped to port my own on the L36. I was actually boring the whole thing through, enlarging by about 3.5 mm. Worked fine, but when I was trying to sand it out with flap wheels I got a little overzealous and went right through the side where the throttle shafts are. Make sure you don't overport! I would definitely pick up a spare TB to work this on, as you'd be down for a while if your stocker gets fubar'd

 

[welby]

Thanks for the extra info Atrus, a very good point. I forgot to mention to add some loctite to the bolts when you re-install them. I also used a cut-off wheel to cut the bolts down on the back, and in doing so the threads will round off and make it very difficult for them to back out on their own.

 

[myjeepwalks]

Awesome write up!! To those that have done this is there a noticable increase in power?

 

[KJ2005]

Simply put, for better flow/less obstruction of flow

The shaft is a cylinder with a notch in it that the throttle plate slides into. So you have half of a cylinder on either side of the plate. You cut it to remove the front half of the shaft, leaving just the back portion of it (the part with the threaded holes, the front holes aren't threaded).

I can dismantle my stock TB later on and get more pics if you'd like. Thanks for the question.

-Marc

can you feel the difference when driving?

 

[tour96se]

to add a few things...on the contour/cougar boards we also do this...what we do differently is knife edge the outter edge of the tb housing,use countersunk screws to hold the plate in,and shave the rear shaft in half,i personally did this service for 21 members and never lost the screws or had a shaved shaft broken. before and after results had the stock 60mm tb flowing approx what a untouched 63mm tb would flow

 

[BjBnet]

no mention on improvements this did???

 

[kj924]

Now if you had the intake and heads ported and polished, I might be able to see it making a difference, but just to enlarge the TB .....naw

 

[boebr1]

i wonder if you just filled in the area before the lip that you ground out, then polished it, and swirled or rifled the whole works... wouldn't you get a greater air velocity through the tb, and cause more fuel to come in? i wonder about that... a venturi action... what would that really do? probably be better to just put a chip in either way

 

[lynxer]

Increase in MPG? More power? What is the purpose? I understand "better flow" but do you really see any improvements?

 

[renegade 04]

I know how old this thread is! I Just wanted to say Thank You to who ever did this write up! I just bored my own throttle body, currently in the polishing stage and will plan on installing in about a month once finals are finished.