I have a friend that has a macine shop and we we're wandering how large can you bore a stock 350 tbi? Is 2" the largest you can bore one?

 

2.13 rings a bell? Maybe it then needs a sleve?

 

By the looks of the 454 TBI (which has the same bore center as a 350 TBI) there isn't much material left between the bores. I would say 2" is the maximum bore.

-Z

 

That's what I was thinking, we're building it to go on my mdified 402 bigblock so i know we need about 700-750cfm's if possible.

Thanks

 

That sounds like it might be stretching the limits of a single 454 TBI, have you even considered twin TBI?

-Z

 

I've thought about that, but havn't seen anything on using a setup like that.

 

I built one for a friends 383 stroker, what would you like to know?

It was based on an edelbrock dual-quad performer air gap manifold, i used a pair of SBC TBI units linked to open simultaneously (as opposed to progressively). The whole setup was run by a Megasquirt-II fuel and spark computer.

-Z

 

check out his threads. great work done here.

https://www.thirdgen.org/forums/tbi/...tbis-dual.html

granted they are 2 single TBI's

 

If I recal you cannot go a full 2" on the stock TBI unit. Many vendors and or people that bore these end up just shy of 2". 2" from what I have read will breach the vacuum ports. I will see if I can dig up a link. Even rebuild and modified Turbo City units are a touch less then 2". I could be wrong though. It has been a long time since I explored doing this.

 

I have a TBI bored to 50mm (just shy of 2") and that looks to be the limit.

 

On that 383 did you use dual 2 barrel tbi's or dual singles? How'd you do the iac and tps for it? Did you just wire them in parelle or just eliminate 1 set all together? The thought I have is to put them on a Weiand dual 4 tunnelram for my smallblock that I'm building. If I had a dual 4 intake for my bigblock I'd do try it out on it.

 

Yes, 50mm is the biggest that they usually bore a stock 305 TBI unit to. It's about 1-31/32". I have one sitting on a shelf if anybody wants to see pictures.

However, the BBC TB is slightly different and has a little more mass so it can be bored out from its original 50mm to 54mm. It's not hard to bore out the BBC TB but it's not easy at all to find the right butterfly plates.

Lou

 

My 2.00 inch throttle plates I bought are Holley Dominator BUT I dont know the carb part distributor I bought from. That was 6 years ago. I would think an email to Holley would point in right direction.

 

I found only two suppliers but one went out of business and I cannot reach the other one. I'll try contacting Holly, thanks.
Would you mind PMing me the part # for them (in case you still have the paperwork)?

Lou

 

One of many receipts that are misfiled. It needed to be drilled for the throttle shaft. I tapped TF added cap screws and used high temp/strenght (permanent) Locktite.

 

[Chevy racer] I was running a pair of stock-bore 350 TBI units to keep the intake airflow speed up. Running dual units allowed me to use stock 51Lb/Hr 350 injectors at ~20psi to fuel a 383. Because both TBIs were mechanically linked i simply eliminated one of them. As for the IACs they are effectively wired in parallel (i built an isolation board, but it's not necessary), however i suspect you could just delete one without any problems.

-Z

 

Here are a few shots of a Rochester 220 bored out to 50mm (1.97"). Any larger than 50mm bore and you're risking going through the IAC passage wall and the outside wall of the unit.





Here's the 50mm unit with a 46mm unit for comparison...