How do I tell if I have the right intake manifolds?

[leadrsa729]

Hello -

I have a 2.4 engine with S cams, ported heads, and 2.0L S pistons. I've removed the MFI for various reasons and have installed a set of 40 IDA Webers. The Webers I was able to find came off of a T engine I think. I've changed the venturis and jets, but I just read something in an email from Ed Mayo about intake manifold sizes and that they are different between T's and S's.

Does anyone know what the difference in size is, and which one should be on which? The intakes I have came with the carbs so I'm assuming they are the T size, and that the larger size would be for the S.

Thanks everyone!

[Flieger]

Intake port sizes varied. You should match the manifold to your heads if they have been ported and polished larger than factory spec.:
911S 2.4 liter:
36mm intake/ 35mm exhaust

On 2 liter cars, 911T and 911S had same port sizes.

Valve diameter for 2 liter 911S and 2 liter 911T:
42mm intake/ 38mm exhaust

Valve diameter for 2.2, 2.4, 2.7 liter 911s:
46mm intake/ 40mm exhaust

Compression ratio 2.0 liter 911T:
8.6:1

Compression ratio 2.0 liter 911S:
9.8:1

Compression ratio 911S 2.4 liter:
8.5:1

Compression ratio 911T 2.4 liter (MFI):
7.5:1

(According to Paul Fere's Porsche 911 Story)

[Flieger]

from Bruce Anderson's Porsche 911 Performance Handbook:

911T 2.4 liter MFI: intake port 32mm/ exhaust port 32mm
--------------------911T 2.4 liter Zenith 40 TIN carburetors: intake port 32mm/ exhaust port 32mm

911S 2.4 liter MFI: intake port 36mm/ exhaust port 36mm

[Flieger]

You say your heads were ported so all these specifications go out the window. Try to match the intake runners to your head port size and shape.

[leadrsa729]

Thanks Max! I ported the heads to 36m. I'll work on getting the intakes to the same size. I really appreciate the info!

[911pcars]

"911S 2.4 liter:
36mm intake/ 35mm exhaust"

Correction:
B. Anderson says: US spec 911S, 2.4: 36/I, 36/E

"On 2 liter cars, 911T and 911S had same port sizes."
S port size: 36, 35
T port size: 32, 32

"Valve diameter for 2 liter 911S and 2 liter 911T":
42mm intake/ 38mm exhaust
S valve sizes: 45, 39
T valve sizes: same as above

"Valve diameter for 2.2, 2.4, 2.7 liter 911s:
46mm intake/ 40mm exhaust"
Correct.

There are enough exceptions to the above to consult Anderson's chart (or equivalent).

Sherwood

[Flieger]

I did notice some discrepencies between Fere and Anderson's books.

[911pcars]

Originally Posted by Flieger

I did notice some discrepencies between Fere and Anderson's books.

Maybe a third opinion is called for: Karl E. Ludvigsen's "Excellence Was Expected"

Sherwood

[Flieger]

I am at school at the moment and that is one of the few Porsche reference books I did NOT bring with me. It is at home on the book shelf. I will consult it in a couple weeks.