I just got off the phone with an engineer at Doug Thorley Headers &
Exhaust systems, and they believe that in most applications
stainless-steel headers are really a waste of money for performance.

If headers are made of a heavy-gauge mild-steel with a good
ceramic-coating, their field tests and years of experience (racing &
street) have shown these type of headers OUTLAST their stainless-steel brothers.

They also cite that stainless-steel headers rate of expansion is too
quick and have had many customer's stainless-steel headers crack after a
hill-climb or a long high-speed drive.

They recommend stainless-steel in the areas that collect condensation
(e.g., catalytic converter, resonator, muffler) and if cost permits the
tubing from the catalytic-converter and back.

Opinions? Thoughts?

Thanks,

:-) neil

Stainless steel is slightly more predisposed to cracking. Mercedes 2.3-16 headers have a 3/8 inch thick steel flange and thick stainless pipes. (Magnet test.) I have supersprint stainless headers on my 190e 8v and they are fine. Supersprint currently MFG's headers for mercedes and they are all SS. Doug Thorley is very well respected in Cali. and they can do a custom setup for almost anything. If you coat mercedes headers I guarantee that you must use an ultra high temp coating. Mercedes exhaust is extremely hot in late model cars and will peel the standard 1300 degree coatings.

Also...do not coat the inside of any header you have custom made, if you are running a cat. Good luck.

PS: Stainless usually cracks when not back gassed, or at least that is my understanding...that bubbles form on the inside of a weld when back gassing is not implemented.

Not being a metallurgist, I may be mistaken, but as far as I know whether an exaust system is made from stainless steel, regular cold rolled (mild) steel, hot rolled steel or plastic, does not really affect how the car will run (plastic being the exception for obvious reasons). my point being that the material is not so much the issue.

The only place where SST is advantageous is in the area of corrosion resistance, the reason being, as corrosion starts to form (more often than not from the inside out) it will affect the flow through the system. Not to a great degree, but that is the principle. Where you will REALLY notice the difference in exhaust system performance is when that spot of rust becomes a big gaping hole.

SST is harder and therefore more brittle than mild steel as a result of the increased nickle and chromium content required to make steel "stainless". SST also tends to absorb heat very quickly and does not dissipate it quite so well. It tends to hold onto that heat.

most of your performance gains in exhaust will be in the construction of the system. Are the pipes madrel bent? (a technique which allows you to bend the tubing while maintaining a consistent I.D. You'll notice on cheap exhausts (ie. Midas or most OEM) where an exhaust tube bends, the material on the inside of the bend is displaced towards the center of the tube, thus restricting flow, thus creating additional backpressure, thus reducing power output.

The key is to find a mandrel bent, free flow exhaust. The material won't make the car go faster. Stainless is in fact, heavier than mild steel.

Stainless just helps you not have to pay $1200 for a custom exhaust every 2 years because it keeps rusting out.

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Cheers!

Yen-Hsen Liem
'93 500E black pearl/black leather; 89,000km; 245/45-ZR17 Michelin Pilot SX; 17x8.25 factory EvoII
'93 500E bornit(blackberry)/black leather; 69,000km; european delivery; 245/45-ZR17 Michelin Pilot SX; 17x8.25 factory EvoII
'88 560SL desert taupe/dark brown leather; 89,000km; Euro headlights
'87 190E 2.3-16 black pearl/black leather; 55,000mi
'70 280SL white/red; 135,000mi (original); factory alloys; Euro headlights

[This message has been edited by yhliem (edited 09-17-2000).]