Has anyone had any work done on a TBI boring it out larger than 2"? I wonder if this could be done. Sure would be nice to have a TBI with butterflies like the back of a quadrajet.

 

I've seen 'em with bores of 2-1/16".

RBob.

 

Can a machine shop do this?

 

yes a machine shop should be able to do it

least I know they could the the throttle body on my car


but honestly your money would prolly be better spent in other places

the gain you would see from doing this would be very marginal if any at all


the stock throttle body flows more then the motor could prolly handle right now as is, and by making it be able to flow even more then that would almost be poinless... maybe 2 hp or so


spend the money on heads, cam, exhuast or something else like that where more of a restriction is taking place

 

It might be cheaper to just get BBC TBI unit. Machine shop work isn't cheap. To go to 2" it will need to be sleeved.

And yes, with your setup a larger then 1-11/16" TBI would be a welcomed addition.

RBob.

 

BBC TBI unit? Is that the same set up as the 454 TBI? I am assuming that stands for Big Block something, right?

 

BBC = big block chevy. The 454 is a BBC.

RBob.

 

Thanks I knew that. Don't know what I was thinking.

 

I just picked up another 305 TBI unit to boar out. I'm still trying to figure out how to get the injectors out of the tower/pod however. I'm searching right now, but if anyone has a short answer, I would appriciate it in case I don't find anything.

 

You can use a round piece of steel such as a large phillips screwdriver or something as a fulcrum, and pry them out using a flat tip screwdriver. Just place the phillips on its side near the injectors and then use the lip of the injector and pry it up.

 

I'd like to toss soemthing in here that may not be known. The throttle shaft is offset in the bore.
The side of the butterfly upstream of the shaft has a larger area. This is so manifold vacuum tends to pull the throttle shut as opposed to open. So don't be surprised or think that the TBI is bad because of this.

I believe Quadrajets have 2" secondaries if you need a butterflys. Gotta' be something good about having a carb laying around!

RBob.

P.S. Here's a pic to go with iroczrockz injector removal post.

 

Yeah, yeah that is what I meant.

 

Well, I just took some pliers and pulled. They popped right out. Now I'm working on making the FPR adjustable. I'll be done with that by the end of the day. I'll also try to get the blades out of there and keep stripping the thing down. I've dumped most of the parts in the can of carb cleaner. Looks like it came right from the factory. Hopefully it will stay that way for a while.

Thanks for the help. I'll be sure to post here again when I get it closer to being done.

 

what is the stock bore on the TB?


and do you know what the CFM rating on it is?

 

Stock bore is 1 11/16ths as stated farther up in this thread. Stock flow rating is somewhere in the 400cfm area.

Boring the TBI won't do much good with 1 11/16 inch holes in the intake so remember they need to be bored to match as well.

Turbo city said they could bore a 454 TBI to 2 1/8" without sleeving.

 

Do you know if sleeving will defeat the purpose at all? If it doesn't then seems like a good thing to do. I wonder if they can go to 2 1/8 with a 1 11/16 stock bore? I bought my TBI from them.

 

As long as the sleeve has a thin wall no big deal. A steel sleeve only needs a .007" wall thickness to be sturdy.

Can't go 2" on a 1-11/16" TBI w/o going through the wall. The only real problem with big TBI bores is fitting it to a manifold. A square bore 4bbl manifold opening is 3-5/8" across. A 2" bore TBI is going to be ~ 4-1/4" across the bores. I used a 1/2" thick spacer to funnel the wide bore to the 4bbl manifold. Then opened the sides of the manifold a tad.

If I had the money (or had to spend the money on new injectors and machining) I'd just go with a Holley 4bbl TBI.

RBob.

 

Yeah, a 4-barrel set up is pretty expensive for sure. I was thinking maybe one year for taxes that would be a good idea. I wonder what the difference would be between the 4 barrel setup and the TBI to EFI conversion setup would be. Besides about a grand.

I emailed Turbo City about boring out the TBI and they haven't answered yet.

 

Just got an answer back from Vic at Turbo City about the boring of the TBI. He said that the unit I bought from him was bored out to 1 13/16" with larger throttle blades and it is bored out as much as it can be. I guess I will have to get a different TBI unit if I want it to get any bigger.

 

I bored one out to 1 7/8" but I had to plug the holes for the port for the charcoal canister. I haven't used it yet because my stock size TBI with ultimate tbi mods is flowing enough air for my setup all the way to 6000. I know this because I have made some WOT passes with WinALDL conected and watched the MAP. I know 1 7/8' is not alot bigger then 1 13/16" bot it's got to be good for a few cfm. Irock, what's your turbo city unit supposed to flow?

 

He told me it was 590 cfm. When I first bought it, I thought I was getting the 2" one but by the time I figured it out I had already used it.