S intake stacks ID diffs
 

Could somebody (Warren?)give me some
definitive answers on the differences
between the Inside Diameters of S stacks.
The metal stacks (2.0 & 2.2) compared to the
plastic stacks (2.4S and 2.7RS+). I have
a very reasonable fellow claim that the
2.2 Euro S stacks are equal to the
plastic 2.4 S stacks. Thanks in advance.

Of course, I have neither in front of
me to measure and the 72-3 Spec Book does
not either.

Bill
72T-->S

I measured mine and they are 36mm I.D. I must say that mine are metal and off my previous 2.2.

[This message has been edited by adgx (edited 12-15-2000).]

Good question, Zotman.

For that matter, are the 2.4S and 2.7RS identical? The reason I ask is that my 2.7RS motor began its life as a 2.4S. I believe and am hoping that the peripheral components were either compatible or upgraded appropriately. Case in point, the stacks, the distributor rotor (for rev limiting), the injection pump, etc...

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John
73 911S

John,

According to the factory service manual, the only difference between 'S' and 'RS' injection throttle housing is that the idle bypass ports were enlarged from 3.3 mm to 4.0 mm. No other changes mentioned, though the injection pump was a different number, and it did have a different space-cam internally. Pacific Fuel Injection has those 2.7 space cams and can rebuild your pump to RS 2.7 specs.

In addition, the distributor had a different advance curve, and was a different part number. The rev limiter was the same part as 2.4 'S.'

------------------
Warren Hall
1973 911S Targa

I whent back to the metal for my rebuild because I could adapt the K&N's easier. I believe the bottom part that mates to the throttle bodies is the same. The top part is a smaller bore, I had mine widdened to I believe 45 or 46mm which is what the plastic intakes are.

The determiner of intake diameter size is the model (T,E, or S),not year or material.

If you look at the chart in Bruce Anderson's book, the intake port for a 69S (uses magnesium stacks) are the same as the 71S 72S and 73S or 73RS (uses plastic stacks).

I removed the plastic stacks on my factory 73RS motor and am actually running with a pair of magnesium stacks from a 69S.



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Carlo
http://bigblue111c.tripod.com/dec2000/

Correction to my earlier post.

The 70S and 71S stacks were magnesium as well which is what is on my RS (magnesium stacks bolted on to throttle bodies from a 73S).

The 69S stacks, though same in diameter, I believe has a different bolt spacing than the later 70S - 73S stacks.

Check out the 73RS lightweight in Adler's book. The stacks don't look like the plastic kind!

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Carlo
http://bigblue111c.tripod.com/dec2000/

Good info, Warren!

So my stacks are probably fine. Can't imagine the idle bypass circuits making a meaningful difference.

As for the distributor, do you have the part number for the RS? I did check my MFI pump and it appears to still be of the 2.4S vintage! The number is 0408 126 021. I believe the RS pump is ends in 019.

Some of you may have followed my earlier threads and my recent HP loss (still unresolved but leaning towards incorrect cam timing). Prior to the valve meets piston episode, this car screamed! I have to believe that the 2.7RS space cam in the MFI pump and the correct distributor advance curve would only delight further! Wouldn't these two things make a SIGNIFICANT difference? I'll have to check my distributor, but if those two things are still the 2.4S components, then it sounds like I have some obvious upgrades to pursue!

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John
73 911S

So from the table in Anderson's
book on pages 110-111. Carlo you
are interpreting that the S intake ports
size diameters are the same, therefore the ID of the stacks above them are the same as well. Interesting. The RS and Ss for all
the street MFI years have Intake port diameters of 36mm whereas the MFI T & E
had 32mm IDs. Are the metal stacks more desirable then the plastic?
My question would be are the diameters
the same down the whole lenght of the stacks from the top to flappers?

Bill

nice 72S Carlo on your webpage.

Thanks Bill, i really enjoy that car!

As to the desirability of one versus the other,it really depends. If you're looking for authenticity, maybe the plastic ones are more "correct". I have heard that the metal ones are more easily bored out, to accommodate a bigger motor/air flow.

I even heard someone mention that the reason he has the metal one is that it won't melt in an engine fire!

For me I just wanted to try something different. It gives the car a more "early" look in my mind. It runs just as great, the only thing I noticed is that when I first did the swap, it seemed harder to start when cold.

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Carlo
http://bigblue111c.tripod.com/dec2000/

The top bore of the Mag stack is narrower, I believe. One advantage to the metal ones is the ability to put K&N's on for the more competition look. Suposedly though when they went to the plastic, although one could conclude that this definately was a cost saver as well as maybe a little weight Porsche also claimed better "Harmonics" or something like that. What ever that means. Also a draw back is the metal ones did not have the plastic injectors in the side for the cold start circuit. Mine did have the holes bored into them and I did use mine from the plastic ones.