Ultimate TBI, Part 2

By Pablo Morales (olbap@bellsouth.net)

OR
How to make your stock TBI flow substantially more with a dremel too, band saw, and some drill bits

The stock TBI unit is a very dependable design. Not streamlined for performance but rather for longevity. This is why designers didnt see fit for it to be optimized for the best flow characteristics. They have however left plenty of room for improvement on the casting. This is where a creative mind and a dremel tool come in. The following will work best (Or work at all) If you have allready gone to the non drop base aircleaner. Follow along and you too can have a high flowing TBI. REMEMBER, WEAR EYE PROTECTION! IM NOT KIDDING!

THROTTLE BORE RIDGE REMOVAL
With the TBI unit removed from vehicle and fuel meter assembly removed from throttle body take notice of the raised ridges around the throttle bores. They force the air taken in by the engine to not only squeeze in between the edge and the injector pod but they also force air to enter primarily from the top. A sure fire way to remedy this is to simply remove the ridges and radius the edge inwards towards the throttle bore. With a high speed cutting bit and a dremel, removal is a peice of cake. I started by just taking off the ridge. Once I had the edge about even with the throttle body surface I began to angle the dremel and radius the edge inward till it was a smooth transition without a ledge. I used the the first outward turn in the bore as a reference. I basically dremeled the best radius all the way around about keeping the same distance from the first edge in the bore. After I got it about where I wanted it I pulled out some fine grit sand paper and hand sanded the edge to an almost polished smoothness. In the process I took out any imperfections the dremel might have left. Dont put together the TBI and slap it on the car just yet. You have more to go.

SHAVING THE THROTTLE SHAFTS
You will have probably noticed by now that the throttle shafts (The things that the throttle blades or plates are bolted to) Take up a considerable amount of room in the throttle bore. Not only does this inhibit airflow but it also inhibits fuel atomization. Best solution is to grind them down. Again use of the dremel is required. If you dont use eye protection at this stage kiss your vision goodbye. Instead of a high speed cutting bit. A grinding bit works better on the harder steel and the screws that im convinced are made of a diamond that just look like metal. Work the grinding bit from side to side until you get the shaft probably 2 mm thick or so, use your best judgement. Becarfull not to run the dremel into the side of the throttle bore as it will gouge it easily. Use the throttle lever to get a good angle from both sides opening and closing the blades. The screws are made of an especially tough metal so be prepared. Your not done just yet, theres more!

PREPARING T.B. FOR EXTRA LARGE INJECTOR SPACER
The only thing limiting the width of the injector spacer on our TBIs is the interference with the back edge of the throttle body and the fuel line fittings going into the injector pod. The neccesary solution is to "clearance" the back edge of the TBI unit for the fuel line fittings. Use the high speed cutter once again to make deeper grooves for the fittings. The depth of the grooves is dependant on your decision to the width of the injector spacer you will use. This one is pretty easy and self explanitory.

INJECTOR SPACER
I used plastic that could take a decent amount of heat to make my injector spacer. It doesnt have to be super tough as it is on a reletively cool part of the throttle body and is not subject to manifold vacuum or being doused with fuel. I made mine close to 1/4" thick. THe stock gasket makes a good template. Use the band saw, or scroll saw to go around all the curves. To take out the portion in the middle feel free to cut into it from the back side, you can always put a small bead of glue in the crack later but I didnt feel it was neccesary. Once you have the spacer put the throttle body back together. You may very well be able to use the stock screws. If not, it is a common metric size that any hardware store carries.

At this point you can put the TBI back together. In fact you can do this one step at a time. Theres no reason to do it all at once except for you will have it off and its better to get it over with. Also you will notice a bigger gain. If you allready have mods like exhaust to go along with your free’r flowing TBI you might be a little starved for fuel. This is what the next volume in the Ultimate TBI series adresses. HOW TO MAKE YOUR STOCK FPR ADJUSTABLE

***The preceeding was for educational purposes only and is not intended as a guidline for modifying any vehicle. Read at your own risk.*****