MFI Throttle Body Bore Sizes

[Jeff Higgins]

I have a couple of sets of later (I believe '72) MFI throttle bodies, one set are stock "T" and the other set has been "rebuilt to 'S' spec" according to the guy I bought them from. Both sets are identical as far as the throttle plate sizes and the bore sizes above the throttle plates, which appear to be 38mm. The only difference I see between them is the size of the tapered bore below the throttle plates. The stock "T" is 29mm and the reworked ones are 36mm (at the largest diameter, where they mount to the heads). Is this correct? In other words, did the "T" and "S" throttle bodies share the same throttle plate size?

[kenikh]

Geez, I sure don't think so. Let me go measure. Back in 2 secs.

[kenikh]

Anyhow, here’s what I found on my TBs: The bore from bottom to the throttle plate is 36mm, but on my ‘69S TBs, the bore actually cuts in right before the throttle plate, so my throttle plate is closer to 37mm. Hope this helps.

[Eric911S]

Hello: Yes, the butterflies are all the same diameter. Thanks Eric

[schmidt]

Correct all the throttle bodies have 38mm plates from 69-76 on MFI cars. The base bore is:

29mm T
32mm E All years
36mm S-RS-G model Carrera.

[Jeff Higgins]

Thanks for the answers, guys. So I guess it really is that easy to make "T" throttle bodies into "S" throttle bodies. The only real trick is in getting the proper taper. I seem to remember reading somewhere that the air bypass passages are a little different; is there anything to that, or is it anything to worry about?

While we are at it, I forgot earlier to ask about the stacks. I have a couple of sets of plastic "T" stacks as well. I would like to have one set bored up to "S" spec. What size would that be? It looks like a straight cylindrical bore, with no taper or venturi at all (and plenty of wall thickness), so it should be pretty straight forward to bore them larger. Is it really that easy?

[schmidt]

The S stacks in plastic are indeed tapered, they are 46mm at the top and........38mm on the bottom.....double check....I think that is right. I have heard of boring the plastic stacks however I have no experience with it.

[JKH]

T reamed to S , tapered

[fryardds]

While we are at it, I forgot earlier to ask about the stacks. I have a couple of sets of plastic "T" stacks as well. I would like to have one set bored up to "S" spec. What size would that be? It looks like a straight cylindrical bore, with no taper or venturi at all (and plenty of wall thickness), so it should be pretty straight forward to bore them larger. Is it really that easy?

Jeff,

I know Matt Blast at Eurometrix can correctly bore out T plastic stacks to S/RS specs.

[911scfanatic]

Henry @ Supertec does it as well.