Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 23

Thread: Original muffler (exhaust silencer) material

  1. #11
    Member #226 R Gruppe Life Member #147
    Join Date
    Feb 2009
    Location
    Portland, Oregon
    Posts
    2,092
    The stainless 2nd wrap is thin and the magnetism comes thru from the inner ferrous muffler.

  2. #12
    Senior Member
    Join Date
    May 2012
    Location
    UK
    Posts
    1,853
    Arenít the ones without the stainless wrap also four layers to but just with both layers regular steel?

  3. #13
    Member #226 R Gruppe Life Member #147
    Join Date
    Feb 2009
    Location
    Portland, Oregon
    Posts
    2,092
    Not that I’ve ever seen. Regular 2 layer, stainless 4 layer. I’m talking old mufflers, don’t think it applies to new manufactured mufflers.

  4. #14
    Serial old car rescuer Arne's Avatar
    Join Date
    Aug 2011
    Location
    Eugene, OR
    Posts
    1,842
    Quote Originally Posted by gled49 View Post
    The stainless 2nd wrap is thin and the magnetism comes thru from the inner ferrous muffler.
    Since my outer layer has small rust spots (pin holes) I'm still pretty confident it is not stainless.
    - Arne

    Pretty much done
    - 1972 911T coupe, Silver Metallic, Fuchs, Appearance Group, F&R sway bars, factory installed Frankfurt, upgraded factory A/C.

    Sold - 1984 911 Carrera coupe, Chiffon white; 1973 914 2.0, Saturn Yellow; 1984 944, Silver Metallic

  5. #15
    Senior Member
    Join Date
    May 2012
    Location
    UK
    Posts
    1,853
    Quote Originally Posted by gled49 View Post
    Not that I’ve ever seen. Regular 2 layer, stainless 4 layer. I’m talking old mufflers, don’t think it applies to new manufactured mufflers.
    Interesting. Yes only taking those mufflers known to be circa 72/3 as demonstrated by date stamps as my question was about how it was in that period — and if it changed to stainless outer wrap in that model 73 period.

    My 1072 stamped one (pictured on post 1 ) is definitely four wrap and it has stainless outer layer — very evident as grey paint is stripped. I would need to check the 672 in more close detail to count the layers and see the material of the outer layer. It is in storage but I recall it is painted but from what I recall does have some surface rust spots (but no perforations). Pretty sure it is regular steel but can double check more closely.

    Other input with examples would helps figure out the answer to my query.
    Last edited by 911MRP; 10-27-2021 at 12:34 PM.

  6. #16
    Member #226 R Gruppe Life Member #147
    Join Date
    Feb 2009
    Location
    Portland, Oregon
    Posts
    2,092
    The stainless wrap is probably not a high grade stainless like 304. Engine on left is new Dansk mile steel muffler, the one on the right is an 84 date code Leistritz stainless muffler for long hood application. FWIW
    Attached Images Attached Images   

  7. #17
    Senior Member swisscheese's Avatar
    Join Date
    Jan 2003
    Location
    The Netherlands
    Posts
    330
    (as posted in Robert's thread as well: https://www.early911sregistry.org/fo...17#post1116117 )

    Performing open heart surgery on a Bischoff 3/73:

    Name:  Bisschoff 3-73 10 ct.jpg
Views: 68
Size:  56.9 KB

    Name:  Bischoff JM Tuning 110122 (5).jpg
Views: 66
Size:  98.7 KB

    The outer skin was in pretty good shape, sans one open spot along the top/bottom seam; The inner skin was rotted away on two large areas, left and right:

    Name:  Bischoff JM Tuning 110122 (3)ct.jpg
Views: 66
Size:  118.8 KB

    This could indeed mean the outer material is different from the inner material (did not perform the magnet test yet).

    On top of the inner skin, there are three small pinholes, to balance-out air-pressure difference between inner and outer skin. In between the shells/skins, there is also a "gaze" damping material. Need to investigate what this is and if I can just replace by modern material (if needs be).

    Name:  Bischoff JM Tuning 110122 (11).jpg
Views: 67
Size:  97.5 KB

    What struck me on the internals, is the pipes are actually flared (coming from pro-audio electro-acoustics this was a nice surprise to see!), improving flow performance. I could see other manufacturers skip this for cost purposes (but tbh haven't seen other muffler internals)

    Name:  Bischoff JM Tuning 110122 (6).jpg
Views: 67
Size:  67.6 KB
    Last edited by swisscheese; 01-15-2022 at 03:52 AM.
    911S 1973
    Early 911S Registry #176

  8. #18
    Senior Member
    Join Date
    May 2012
    Location
    UK
    Posts
    1,853
    Thanks for the information here and on the other post. Interesting that the pipes are not parallel.

    My father was into home ( not pro) Hifi all of his life. I kept his papers on his beloved transmission line speakers (he was a fan of work of Radford and Bailey https://www.keith-snook.info/wireles...0Enclosure.pdf).

    I still have his 70s Radford speakers and Radford amps from Bristol — original classic audio some of which seem to have become collectible especially the Radford valve amps… bit like classic cars of similar era they may not be the most modern but have a certain quality that ensures.

    I remain interested in whether the Bischoff outer exhaust silencer skin is stainless on 373 or regular steel. I expect the former based in my 672 and 1072 examples. Magnet test may not help unless the two layers are apart.

    Steve
    Last edited by 911MRP; 01-15-2022 at 05:33 AM.

  9. #19
    Senior Member swisscheese's Avatar
    Join Date
    Jan 2003
    Location
    The Netherlands
    Posts
    330
    thanks. Acoustics background help a lot in understanding mufflers (Helmholtz resonators, organ pipes, quarter-wave pipes, etc.) and how to tune/tweak them (droning inside car). When I'm back at the muffler, I'll do the magnet test on the outer skin and see what happens.
    911S 1973
    Early 911S Registry #176

  10. #20
    Senior Member
    Join Date
    May 2012
    Location
    UK
    Posts
    1,853
    Leading Automotive engineering companies have a lot of skills and invest in significantly in facilities. When I was a director
    at Lotus Engineering Ltd we had both whole vehicle and engine acoustic chambers at Hethel. Vehicle NVH was a core competence as was powertrain. Also pioneering work in electronic noise cancellation. I believe with EV the management of is an interesting area. Porsche were a direct competitor in offering engineering consulting to OEM clients and has significant facilities for its own car products including a full anechoic chamber for vehicles

    Steve

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Message Board Disclaimer and Terms of Use
This is a public forum. Messages posted here can be viewed by the public. The Early 911S Registry is not responsible for messages posted in its online forums, and any message will express the views of the author and not the Early 911S Registry. Use of online forums shall constitute the agreement of the user not to post anything of religious or political content, false and defamatory, inaccurate, abusive, vulgar, hateful, harassing, obscene, profane, sexually oriented, threatening, invasive of a person's privacy, or otherwise to violate the law and the further agreement of the user to be solely responsible for and hold the Early 911S Registry harmless in the event of any claim based on their message. Any viewer who finds a message objectionable should contact us immediately by email. The Early 911S Registry has the ability to remove objectionable messages and we will make every effort to do so, within a reasonable time frame, if we determine that removal is necessary.