Injuneer

You get them cera-metallic coated (e.g. Jet-Hot) and you get the benefits of wrap (cooler under hood temps, improved scavenging due to heat retention in the primaries) without the problems of excessive tube metal temperature causing corrosion and thermal stress cracking. Mild steel was not meant to function at temperatures in excess of 1,000*F.

Old story, but one of the early LT1 parts suppliers, Tom Byrne, saw his Z28 go up in flames when oil leaked into the wrap, soaking it, and caught on fire.

My HPC coated AS&M headers are now 18 years old, and the only rust is some very tiny spots on weld spatter where the primaries were welded to the head flange.

DarkKnight

Yeah, I've heard more negatives about wrapping headers than not. Even some horror stories as you described.

Is 321 better for heat than 304?

97WS6SCharged

Odds of you ever getting a header to the point where 321 is actually better than 304 is probably pretty small. Personally, I wouldn't spend the extra coin if it's not necessary.

FWIW, I have a set of the "ebay" headers on my 408 LS Z28. Only fitment issue was a slight rub from one of the primaries near the sub frame but that was easy enough to fix. I paid $100 for the headers so I'm ok with taking a hammer to them (literally had to put a dime size dent in one tube). I think I also spent $20 to have the emissions fittings welded closed at a local shop.

DarkKnight

True.

But does 321 contain the heat better than 304?

Injuneer

Stainless steels have lower thermal conductivity than mild steel.

321 is 304 plus titanium stabilizer. The variation in thermal conductivity due to allowable variations in composition of the stainless steel is greater than the minimal difference in thermal conductivity between the two compositions. The metal is so thin that a slight difference in thermal conductivity is not going to be significant.

Stainless steel exhibits a high temperature strength advantage, and resists oxidation and other forms of corrosion. But it will "blue" when exposed to 1000*+ temperatures.

DarkKnight

Wow, you sure know your stuff!

Is the temperature difference that much?

Injuneer

The tests I've seen in automotive magazines indicate the surface temperature of the primaries is reduced between 200-300*F, depending on engine load.

DarkKnight

Oh ok, that doesn't seem like that wide of a difference but Im sure it helps. I think I'm going to go with the stainless headers. Anything is a step up from the shorties I have. I'm more concerned about durability and longevity.

Injuneer

What causes you to feel the durability and longevity of cera-metallic coating is inferior?

streetbad

I just received a set, Same as LPP headers. They look good. I have not installed them yet. Over on LS1tech.com there is discussion of fitment, install etc. The 321 is what sold me (durability). I had mine coated, but they came polished nicely.

DarkKnight

No, no...that's not what I was implying, sorry. I meant the type of metal itself.

DarkKnight

I've heard LPP makes a good header from what I've read aside from fitment issues that I read were on the earlier batches made.

Injuneer

This picture was taken a couple years ago... but looks the same today. The AS&M mild steel headers were originally bought by a buddy of mine in 1997 for his 30th SS convertible. In 2000 when he was trying to push that build up to 1,125HP at the flywheel, he outgrew the AS&M's. I bought them used in 2000, and they have been exposed to big exhaust gas temps with the 300 shot of nitrous. 18 years later, and the only deterioration is the bits of rust on the weld splatter.

I have a bung added to #7 primary for an EGT thermocouple, and even though that was drilled and welded AFTER the headers were coated, there is minimal rust in that area.

Injuneer

Here's photo of an engine with S/S headers.... same buddy, 30th SS convert, but now its up to 1,350HP at the flywheel. The headers are custom made by Lemons, with I think 2" primaries. In this photo, they are about 6 months old, and have pretty much turned black.

DarkKnight

Yeah, I understand your point and they do look fantastic for the age, mileage and high horsepower abuse. The Hooker coated headers I have now look close to that and they are 12 years old. But the coated y-pipe and collectors are rusting away. I'd probably go after AS&M headers but they don't make them anymore, as you said. The black on his stainless headers looks more like a carbonizing effect than rust. Also, I am not running anywhere near that kind of power that you 2 are.