I bought a spare TBI at a swap meet for $7 so I decided to play with it this winter for something to do. Today I am going to barrow a lathe and bore it out. I am going to make my own throtle blades so that gives me some freedom as to what size I bore it to. I am going to stay slightly under 48 MM to be on the safe side. (48MM has been done with out breaking through the casting). I'm shooting for 1 7/8" bores. This should give me some where in the neighborhood of 560 CFM. Should be plenty for a 305.
I will update this project from time to time.
later,Dave

 

Well I got them bored out to 1.875" OK. It was pretty strait forward allthough it is a strange shape to chuck on in the lathe. It would have been a piece of cake to set it up and bore it in a milling machine. The reason I chose the lath was because I wanted to be abile to spin it so I could polish it with some sand paper.
There is a small hole in each bore just above the throttle blade that is routed to the nipple for the charcoal canister. I am guessing that it is a ported vac sorce that only has vac when the throttle is cracked.
Does any one know how this system works?
Is it necesary for opperation?
Do I even need the canister?
The reason I asked is that in the process of boring I broke into the cavity that the small hole is connected to and the hole became a slot about 5/16" long. I pluged it for now with a metalic epoxy. If I need this system to opperate I will drill the small hole back out in its origional location.
Side note: the trottle shaft is offset in the bore about .032" being closer to the back of the unit. It doesn't pose any problems, I'll just offset the holes in the throttle blades when I make them. I guess I was expecting them to be on center.

My next step is to mill the ridges off and radious the bores.
I have not yet decided if I will shave the trottle shaft. It doesn't seem like you could take much off without weakening it.
Later,Dave

 

teh canister is only used for post shut down emsiisions. no state in the country has enstated testing fo rit yet and they are not likely too since most of these canisters stop working wiht in a few years of the production of the vehicle. teh charcoal canister has a check valve in it that holds vacuum, then when you turn the car off a signal is sent to open up the valve and draw the unused caharge out of the intake and into the caister to be recondensed into fuel. it is a very poor system and can only grab a few drops of fuel under perfect conditions

later
tim

 

I bored mine out to 48mm last spring. I had the same thing happen with the little holes for the charcoal canister. They turned into huge slots. What I did was made a small aluminum rod about .001" bigger than the hole and I pressed it in. Then we put it back on the mill and cleaned it up since the rod was protruding into the bore a little bit.


This pic you can see the bottom of the rod I pressed into the hole
http://groups.msn.com/V8AstroCaptain...oto&PhotoID=88

This one you can see how the rod filled the slot in
http://groups.msn.com/V8AstroCaptain...oto&PhotoID=90

I used throttle plates from a stock TPI throttle body.

 

Thanks for your help guys. I'm thinking that the canister is going to dissapear one of these days. It will probably reappear some where in the galaxy next to my smog pump, air tubes, egr, and cat.

 

I finished making throttle blades today. I made a fixture to hold them in the lathe and turn them locating on the screw holes. Took about four hours total. If I could have found a pair of 48MM blades I would have gone that route, but it didn't happen so I had to make them instead.
All's well that ends well I guess.
I feel like I have all the tricky work behind me now. Going to mill the ridges and radious the bore next. I consider that the fun part. It would have made more sense to do that before making and installing the blades, but I was alittle nervous about the blade thing working out and wanted to get it behind me.
I think I'll make a injecter pod spacer out of 1/4" aluminium also. Well I guess supper is ready.
Later Dave

 

man, i wish i would have known, i have a pair of 48mm blades that i could have given you

 

These guys maybe have had some that you needed.

http://www.braswell.com/html/throttl..._base_pl.html#