correct diameter for ST or RSR twin outlet pipe

[JBQuick]

Hello all, looking for advise as to what is correct diameter for the ST or RSR twin muffler outlets. Is it 2.25", 2.5", 2.75" or bigger ???

TIA !

[Flunder]

Yes, BIGGER!

The outside diameter of the twin outlet pipes on the factory ST/RSR rally silencer is exactly 7.0 cm. This dimension is equivalent to a diameter of 2 and 13/16 inches.

This is the muffler used to match up with factory tubular exhaust headers or "spagetis" and short megaphones or "diffusoren."

This style muffler was used in 1970, 71 and 72 on 911ST and 914-6GT and later the 2.8 RSR.

Here are some photos. The two upper images are of a 911ST/RSR system. Note old time factory nickel plated spagetis.

The lower image is of the 914-6GT set up. Note the difference in where the outlets are placed.

The GT set up reputedly came off the Sonauto LeMans GT Class winner. The 6 GT headers are also shown.

[Flunder]

The red 1970 ST is shown with the exhuast set up as it would have been used for tarmac stage rallys on public roads. The main outlets are capped and an added ancillary pipe in the conventional location is opened.

The other image shows a factory original race department engine in 2.5 short stroke configuration with 906 center oiling cams, 41mm high butterfly and a complete race exhaust showing spagetis, diffusoren and rally silencer. This was exhibited for sale at the recent Essen show.

[Chuck Miller]

Hey Tom,

This is good info...

But...

I think you put the decimal point in the wrong place...
I think you meant to say 70mm or 7cm not 7.0mm

Also, it looks to me that 70mm is almost dead on 2 3/4"... what'cha'think ?

Cheers,

[Flunder]

Chuck - thanks; yes of course 7.0 cm.

On the Aeroquip mic looks like 7.0 cm equals 2 13/16 to me.

But I am farsighted as well as prone to drop decimal places!

[OliveR]

Yes it's 70 cm
does someone know how source(at realistic price) quick release clamps,and megaphone clamps?

[tomkirkcis]

Has there been any atempt to catalogue the various part number for sport mufflers? This thread peaked my interest to look on my shelves for an old sport muffler I had not looked at in many years. It appears common variety, is made by Leistritz and has part number 901.011.09/07.

Having a 914-6 I am familiar with a site that has some interesting early exhaust images. http://www.pbase.com/9146gt/rally_muffler_of_a_gt
One image shows an outlet being measured with a caliper. tom

[Flunder]

Tom;

Thanks for posting the link. The site shows a copy of the Werkfoto with all the parts complimentary to the rally silencer.

It would be nice to be able to buy everything at one time and know that it is all going to work together!

Shown are the tall magnesium 906 intake manifolds (or "suction pipes" as the factory literature calls them), 46IDA-3Cs, three journal 906 cams, 27mm neck Marelli twin spark, twin plug heads, 10.3 p&c etc. The spageti and diffuser both look to be finished in old time factory nickel plate.

Interestingly, the Werkfoto photographer chose to show a 911 header. However, it is the header for the right side but displayed as if it was for the left cylinder bank. It is with a silencer that appears to be the one for a 6GT - note that the outlets are mounted well inboard. I suppose the man behind the shutter found this mix of bits best for a more symetrical composition.

The kits were available for either model range.

[pu911rsr]

Does anyone sell repro's of the RSR muffler, I need one for 73 Replica.
Thanks,
Phil

[Flunder]

Phil:

I think OliveR has complete systems.

You could also consider getting the muffler shop to mod a standard muffler to get the "look" using some 2 3/4" pipe ( as Chuck points out) and retain the use of your heat exchangers.