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Noah Holcomb's Avatar
 
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Lightbulb OBX, GSF, and Schnell header dimensions and materials data.

Has anyone measured the OBX, GSF, or Schnell header's primary and secondary inner and outer diameters? The GSF, OBX, and Schnell headers list different dimensions for these sections. The tube thickness/gauge varies not only by the advertised brand but from vendor to vendor! Also the advertised material composition on these headers is not the same. However many have said they are the same headers sold under different names. This leads me to four possible conclusions.

1. All of these headers are the same and some sellers are giving incorrect dimensions.

2. They are indeed slightly different designs using different materials and dimensions.

3. The factory uses whatever material it can source in a set price range that meets basic design parameters.

4. The design is receiving constant revision and updated as needed, this causes the variation of specifications.


The following list the parameters I have been able to locate for each header.

*** indicates disambiguous information within a brand that varies between vendors.

Brand: GSF headers
Material: 304 stainless steel
Primary diameter: 38mm (inner or outer diameter was not specified)
Secondary Diameter: 50mm (inner or outer diameter was not specified)
Tube thickness/gauge: 1.5mm

Brand: Schnell headers
Material: *** 304 stainless steel *** 321 stainless steel ***
Primary diameter: 35mm inner diameter
Secondary Diameter: 50mm inner diameter
Tube thickness/gauge: *** 1.5mm *** 14 gauge (approximately 0.83"=2.1082mm) ***
*NOTE* Headers listed with 1.5mm tube thickness were advertised as 304 stainless steel
*NOTE* Headers listed with 14 gauge tube were advertised as 321 stainless steel

Brand: OBX headers
Material: 321 stainless steel
Primary diameter: 41mm inner diameter
Secondary Diameter: 56mm inner diameter
Tube thickness/gauge: 14 gauge (approximately 0.83"=2.1082mm)

Initial conclusions.
The GSF headers based on their advertised tube thickness of 1.5mm and assuming the 38mm primary dimension was the outer diameter yields a 35mm inner diameter. This leads me to believe the GSF and Schnell as they share many of the same specifications depending on how viewed are the same header. As the Schnell and GSF are listed as 304 stainless, and the Schnell is also listed as 321 stainless by some vendors makes me believe both headers are indeed made of 304 stainless and any claim of 321 stainless in reference to the Schnell design is false. I still am not sure if the OBX headers hold to their claimed specifications.

Last edited by Noah Holcomb; 06-01-2007 at 01:08 PM..
Old 06-01-2007, 09:12 AM
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5. All of the above.

I know nothing of these headers except for the price. It is very unlikely that a significant amount of 321 could be used, even in China, and sold in the US for those prices. I deal with all types of stainess every day and use 321 in the 930 exhaust systems that M&K produces for me. It is ungodly expensive; both to purchase and to weld.
Using lesser grades of stainless in a turbo application reduces the longevity of the product. How are these headers holding up, anyone know?
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 06-01-2007, 09:41 AM
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So many questions get asked about them, at least one example of each header has likely been purchased by at a forum member that can verify and post some dimensions. That way some of the basic questions regarding these headers can be put to rest.
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Last edited by Noah Holcomb; 06-04-2007 at 04:19 AM..
Old 06-01-2007, 09:51 AM
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Good discussion.

Is there any way for an at-home average Joe to tell what his headers are made of?
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Old 06-01-2007, 12:06 PM
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Do you own a hardness tester or have access to one?
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Old 06-01-2007, 01:14 PM
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I don't - would one of the $25 units here do the job?

http://search.ebay.com/search/search.dll?sofocus=bs&sbrftog=1&sacqyop=ge&catref=C5&saaff=afdefault&sacur=0&fcl=3&nojspr=y&frpp=50&from=R10&saslop=1&fss=0&satitle=hARDNESS+TESTER&sacat=-1%26catref%3DC6&sargn=-1%26saslc%3D2&sadis=200&fpos=98033&ftrt=1&ftrv=1&saprclo=&saprchi=&fsop=1%26fsoo%3D1&coaction=compare&copagenum=1&coentrypage=search
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- Craig 3.4L, SC heads, 964 cams, B&B headers, K27 HF ZC turbo, Ruf IC. WUR & RPM switch, IA fuel head, Zork, G50/50 5 speed. 438 RWHP / 413 RWTQ -
"930 is the wild slut you sleep with who tries to kill you every time you "get it on" - Quote by Gabe
Movie: 930 on the dyno
Old 06-01-2007, 01:19 PM
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Some good reading, I would source some info from a few excellent material science books but I am already home from work.

304
http://www.azom.com/details.asp?ArticleID=965


321
http://www.azom.com/details.asp?ArticleID=967

In short 304 and 321 perform similar in many conditions. 321 really starts to shine at temperature of 600 C (1112 F) and up. The only difference in the composition of the two is 321 alloy has small trace amounts of Titanium. 321 does have a higher hardness value (not by much) If there are no plans to post-weld annealed it is easier to make welds that survive with 321 than 304 when the temperatures start to rise. 321 and 304 are very similar in terms of behaviors at lower temp ranges.

Last edited by Noah Holcomb; 06-01-2007 at 02:11 PM..
Old 06-01-2007, 01:40 PM
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Some cheap test instruments are good, some are worthless. One of the primary reasons good test equipment cost so much is the calibration data associated with it. Buy a pressure gauge and it's cheap, now buy with with calibration data and look how much the cost goes up.

You can find some good test equipment on eBay at decent prices if you look around long enough as eBay is not really a big marketplace for such an item. I would still test on metals of known properties first while record results for use in development of any needed calibration data. I would at the very least get a known piece of 321 and 304 for reference data.

The cheapest and easiest way to verify the material would be buy a cheap tester, a piece of 304 stainless steel, and a piece of 321 stainless steel. Test both pieces you just purchased several times at different points on their surfaces and record the results. Now test the material of the headers at several points and write down your findings. With the compiled data take the averages for each known specimen and the unknown headers and compare. You could go overboard here and analyze deviation and such but if you only plan on using the tester once or twice don't waste any more time, unless you are like me and enjoy such activity.

Last edited by Noah Holcomb; 06-01-2007 at 02:10 PM..
Old 06-01-2007, 01:54 PM
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Received my OBX yesterday and they look fairly decent. I rushed them out to a well know welder/fabricator to get his take on their quality, but before I dropped them off, my friend used his caliper thingy mabob to take a quick inner diameter measurement.

Primaries were at 36mm
Secondaries were at 48 mm.

They are still at the welders shop to do a little clean up so I won't be able to get the outer diameter measurements until Monday.

Still wondering if I should have them Jet Hot coated...

David
Old 06-01-2007, 08:14 PM
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I weld 321 regularly (3hrs today alone) and quite honestly I don't think I can tell it apart from 304, though when I weld 304 the joints are usually more crude because the applications don't demand such precise fitment so I can't say for certain that someone else has not identified a characteristic which shows up when welding. Spark characteristics when touching materials to a grinding wheel is a method often used to narrow down what a material is, but a quick test with 321 and 304 does not display any obvious difference. - see pictures below.

The dominant attribute of 321 over 304 as it pertains to aviation exhaust systems is it's resistance to oxidation (corrosion) at sustained high temperatures (1000+).

I agree it's nice to know what you are getting when buying a product so as to not pay for bullsh__ marketing, but personally I would not go out of my way spending significant added dollars for 321.

321 can and will crack just like 304. I've seen plenty of cracks in 321 aviation exhaust systems ranging from high hour parts, to a pipe sitting on my bench from a brand new aircraft with less than 50 hours.

Good to see thread which will capture all the details of the different brands Noah.

Even though this quick test did not tell me the difference between 321 and 304 some of you might find this interesting. Examine the sparks from these different materials, look at spark length and tail end.

Spark volume can be related to pressure against the wheel, though some materials produce a higher volume of finer sparks such as carbide of cobalt cutting tools.

Known 304


Known 321 (has the same characteristics as 304 spark)


Known 316 (generally same characteristic of spark as 321 and 304)


4130 (chromolly) low carbon steel: you can see some of the sparks burst at the tail end because the steel is oxidizing from contact with oxygen at high temperature. By comparison, the stainless materials never ignite into a secondary spark.


Here is a Cessna 172 tailpipe made from 321 material, from a high hour application. The wall thickness appears to be about .050 but the oxidation which resulted from sustained exhaust gas heat along with a continuous blast of atmosphere air against the tubing eventually eroded through the tubing wall. I took a pair of pliers and ripped the right one like it was a pop can. If the tailpipe were made from 304 the eroded hole would have occured sooner in it's life. Edit: this tail pipe has seen something in excess of 10,000 hrs flying time, with atmosphere air blasting it at roughly 125 mph.


Edit: excuse me for rambling, I'm bored. Not enough new threads in the turbo forum.

Last edited by Jim2; 06-02-2007 at 07:20 AM..
Old 06-01-2007, 09:53 PM
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