Hello all
I’m looking to increase the performance of my 89 Formula. It’s an automatic with a 3.90 posi. 3 inch exhaust. I’m wondering which aftermarket throttle body would work best for my application? Thank you

 

At this point you are nowhere near needing to spend money on an aftermarket throttle body.

The biggest limiting factors to a TBI engine in stock form in no particular order are this:
1. Exhaust (super restrictive)
2. Cam (a pitiful joke the stock cam is)
3 Heads (the 193 heads are actually pretty decent for a stock casting, good low end and ported they can pull hard up to 5,000 RPM or so....)

Also, if you're serious about getting more performance out of it, you need to learn how to burn your own chips to dial it in. Or find someone who can. The Hypertech and similar "canned tunes" don't really do much, just marketing BS.

As far as the throttle body is concerned:
Research salad bowl mod, and ultimate TBI mods.

GM used a drop base air cleaner on these engines with a little collar underneath it to space it back up, that little collar really chokes off the throttle body b/c if you look at it with the air cleaner off, the injector pod hangs over the bores, so the only way it can induct air is from the sides, which is difficult with that goofy collar that's on there.