Here are some pictures of the side pipes and headers.

First three pictures are of the side pipes.

http://www.clubcobra.com/photopost/d...ide_Pipe_1.JPG

http://www.clubcobra.com/photopost/d...ide_Pipe_2.JPG

http://www.clubcobra.com/photopost/d...ide_Pipe_3.JPG

The next three are of the headers.

http://www.clubcobra.com/photopost/d...0/Header_1.JPG

http://www.clubcobra.com/photopost/d...0/Header_2.JPG

http://www.clubcobra.com/photopost/d...0/Header_3.JPG

I'm going to drop off the side pipes today to see if they can be repaired. The headers are toast, so I'm ordering new ones later today also.

Sure hope this does not turn into a yearly event.

They are cracked in the heat affected zone of the weld, in other words the metal is very brittle in the heat affected zone. May need to go with heavier wall pipe

Very poor workmanship...
 

It's probably not a good thing that exhaust gases can travel from pipe to pipe across the gap in the flange. The exhaust would act like a torch on the edges of the tubes causing overheating and cracking.

I had custom pipes made up for my cammer car last week and while I was inspecting the work I noticed the discoloration of the welds.These pipes are 304 stainless steel and the welds had a brass color to them.The fabricator explained that he used a filler rod that had silicon bronze alloyed with the rod.This created a weld that was somewhat soft and not so brittle so as to crack and leak.I don't know if this is your problem,just food for thought.

Another food for thought. While researching for parts to asemble my headers, I came across an interesting article on the Stahl Headers web site. They gas weld their header joints and braze the flanges onto their headers. They say that gas welding is self-annealing and the brazing allows for a larger fillet, which makes the joint more durable. If the headers are mig or tig welded, the headers have to be properly annealed to prevent premature failure.

www.stahlheaders.com

How do you properly anneal the headers? I'm relatively new to welding and want to learn more.

That's a good question. They don't cover that in the article. Any metalurgists out there?

maybe your timing is not advanced enough (retarded) or the mixture may be too lean. This can cause extremely high exhaust temps that would cause any weld to fail that would not normally fail.


.

Have you checked your mixtures and determined if you are running in spec ?

Or are the mounts too rigid on the motor side, and too weak on the pipe side introducing flex in the pipe junction ?

Iquiring minds want to know.


Steve

The pipes look very white and little or no trace of carbon. If you're not running race gas, I'm inclined to think your exhaust gas temps are way high because of a lean mixture.

David

My original headers and sidepipes had the same flanges which I labeled "Flange 1". Mine also cracked and it was not related to engine tune. There are large gaps where there isn't any flange, allowing exhaust gas to leak to adjacent pipes, which effectively puts the edge of the pipe in the exhaust stream. The edges of the pipes overheated and cracked in those areas. I built sidepipes and headers using "Flange 2", which contains the exhaust to its respective pipe. I have not had any failure in that area since.

http://i589.photobucket.com/albums/s...ld/Flange2.jpg
http://i589.photobucket.com/albums/s...ild/Flange.jpg

slip in
 

We never had problems with slip-in headers, secured by springs (as seen on Ducatis).
Exhaust systems tend to crack because of vibrations.

Thought I would chime in and clear some of the questions here. I apologize in advance to be so long winded !

First of my background is 15yrs as engineer specializing in welding metallurgy

Annealing - to say that you require annealing with a GTAW ( TIG ) or GMAW ( GMAW ) for this application ( carbon steel thin wall pipe ) is simply incorrect. We have clients welding 2" thick mine car wheels with the MIG process and are in service in as welded condition . These wheels look like ovals when they are running. No issues

Almost all carbon steel and stainless welding on cars / trucks is done with GMAW in as welded condition ( no annealing )

Heat Affected Zone Cracking - although at first glance at your pictures we may be able to conclude that welds are "heat affected zone cracking" which is delayed hydrogen cracking which causes brittle HAZ but this is not the case

Reason is GMAW / GTAW process is a low hydrogen welding process. Base material most likely does not have high Ceq ( like an alloy steel ). High quench rate is not possible when welding since material is very thin

Therefore the none of the 3 criteria required for true HAZ cracking due to brittle weld are being met

Oxy Acetylene Welding - there is a very common misconception that a oxyfuel weld is not as brittle as a proper TIG and therefore more forgiving. This is simply incorrect

Please follow the following links to the "certificate of conformance"...the legal document that welding filler material manufacturers require to show their products meet the requirement set forth by the American Welding Society

This is a typical oxy fuel deposit. Please note elongation

http://www.mylincolnelectric.com/LEE...mes=US9025.PDF

This is typical GTAW weld using the proper ER70S-2 filler material

http://www.mylincolnelectric.com/LEE...5_20090522.pdf

As you can see the GTAW filler results in a much higher elongation property. In general terms we can conclude that the GTAW deposit is far less "brittle"

Possible Problem ( highly unlikely however )

- often people who use the GTAW process use the incorrect R45 / R60 filler ( same filler used for oxy acetylene ). You cannot tell the difference looking at the filler. The filler is typically coined or flagged with its type but not always
- the use of oxy acetylene filler with TIG will result is a very poor , highly contaminated and brittle weld
- I see this on a regular basis out in the field. Having said this its highly unlikely Superformance would make this mistake

The most likely problem has already been suggested by others

Quite simply the tubes are experiencing far more stress than the wall thickness can stand.

Evidence that supports this - welds are both in the weld centerline and adjacent to weld. This is typical evidence of a overly stressed weldment NOT OF A BAD WELD. The fact that some of the welds cracked in HAZ is simply coincidental

Why is the flange overly stressed -

As already suggested by others, the high temp creep strength of a carbon steel is relatively poor. If , as others have suggested you are running excessive EGT, the yield strength takes a nosedive

This is , why catalytic converters ( higher temp than the rest of the exhaust ) is typically a Type 409 stainless. Obviously the best would be a high nickel material such as Inconel 625 but that is very cost prohibitive. This is why you only find Inconel in high end race cars

Conclusion - most likely conclusion is a combination of loss of strenth due to high EGT, combined with stress and cyclic loading

My SPF sidepipe hangers have both cracked. Although the design of the hanger should hold and withstand the vibration, they both cracked at a stress riser ( concave weld profile )

It does not take much of a stress riser to cause a failure in a weldment

We do lots of robotic welding of exhaust systems and all the in service failures are not due to bad welding practice but rather weldment is overstressed pass design specifications

Since I stare at welds daily, send them for chemical, mechanical testing etc, I am fairly qualified on discerning between a good and bad weld. I am pleasantly suprised on all the chassis welds of the SPF. They all look pretty darn good !

If anyone is concerned about possible start of cracking on your headers / exhaust the most cost effective is purchase a can of Magnaflux dye penetrant ( don't forget a can of the developer as well )

Hope this helps

Great input for welding!

However, I prefer the slip in exhaust.

First off, thanks to everyone for their input. It's greatly appreciated.

I dropped the side pipes off to Craig Blood at Blood Enterprises to have them weld them up. He agrees, it looks like it's running lean.

Craig did the initial setup of the carburators, but at the time we did this we concentrated on idle and full throttle setup. Since these are race carburators, that is where they were made to run at. One of the things we did notice during the dyno runs was how much throttle it took to transition from the idle circuit to the primary circuit. I would guess that 60% to 70% of normal driving is on the idle circuit. That's probably the problem. I'm going to have them order some Quickfuel primary metering blocks so we can easily adjust the idle circuits.

So after I get it back together and we get a nice day, I will take back and we will work on it some more for part throttle driveability.

I should get the new headers from Hillbank tomorrow, so I will drop them off for coating after I pick them up. Hopefully we will have a nice day or two in February and I can get this resolved.

Once again, thanks to everyone that replied.

Glad I could offer a worthwhile opinion.

Years ago my engine was running so lean it caused the Jet Hot coating to begin flaking off.:eek:

David