Competition Throttle Bodies

[Matt Blast]

Another thread was discussing stack sizes and I didn't want to highjack, so for you Raj (modest?) here is some size-related info for the competition throttles:

2.5 ST High Butterfly, 50mm top throttle plate, bottom size presumably 41mm. Three sets I've measured or had someone measure were 42-43mm on the bottom. At least two of these had been modified for sure. Anyone with an unmolested 2.5 houising casting #911 110 107.2R please measure the port side diameter. Throttle plates, shafts and bushings same as 2.8-3.0.

2.8-3.0 RSR (before slides) and 3.0 SCRS High Butterfly, 50mm top throttle plate, tapers to 43mm port side. Actual bottom measurment is about 43-43.70mm or so, depending on the individual casting. There is some variablity between castings. All else same as 2.5. Bevel angle on throttle plate is specific to 2.5-2.8-3.0 High Butterfly. 8mm throttle shafts. Brass bushings (like street '72 and later but heavier).

934.5 (like in current issue of Excellence, after CIS 934). 41mm throttle plate low in housing. No taper to barrel, Straight through. Angle of throttle plate same as 935, greater than 2.5-2.8-3.0 High Butterfly type. Note that ALL competition normally aspirated housings were tapered, as was the non-turbo street MFI, but the turbos didn't have to be tapered.

935 I've seen two types with different casting numbers. 41mm and 43mm straight through, no taper. High throttle plate. Roller needle bearings for throttle shafts, same as 934.5. The bearings are presed into aluminum carriers which are then pressed in to the housings. Throttle shafts are 10mm hardened unlike the 8mm non-hardened RSR type. Bearings wear out, shafts are robust, 3-piece shaft couplers are always shot.

962 The early aluminum castings have a crude appearance with roller needle bearings pressed directly into the housings without carriers. The bearings are placed close to the inside of the bore but do not sit flush with the round bore. This causes leaks. Later 962 housings had an aluminum carrier for the bearings like the 935 and this eliminated the air leaks. 48mm throttle plate high in the housing with a tapered bore. Non-metric shafts and bearings(what were they thinking?). Throttle plate angle greater than 934.5/935.

Now thats rambling for you. All have a Merry Christmas!

Matt

[Flunder]

Hi Matt:

As to casting numbers:

I understand that the 41mm set as first used on the 2.5 liter ST engines has the suffix "2R" on the casting number.

Is the suffix on the casting number "2.5R" or "3R" for the 43mm set-up as used on the 2.8 liter RSR engines?

Does the SCRS casting have yet again a different casting number?

Merry Christmas!

Tom

[Matt Blast]

Yes the casting number for the 2.8/3.0 is the 5R (911.110.107.5R)

Hey Raj, if you ever take off the throttle bodies please measure the bottoms.

Tom, I know you have the 2'S also. Any measurements would be helpful.

The housing for the SCRS has the same internal dimensions as 2.8/3.0....50mm on top and about 43mm on ther bottom. I didn't note the casting numbers when I had a set. There are external differences that are very noticable. On the outside there are flat bosses with a small hole (about 2mm) drilled into them. As I recall there is one of these per barrel. I don't know what is the purpose for these holes, I just know they appear different on the outside as compared to the early housings.

Matt

[sezme]

FWIW - I just bought a set from Matt and cant wait to see them...

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