Headers: Mild Steel or Stainless

[LUD35]

Hi guys,

before you flame me i did do a search of the forum, and i couldn't find the answer i need.

weighing up getting either custom 4-1 headers by a reputable exhaust workshop in brissy, or buying R-Crew 4-2-1's. i want 4-1's guys but i might have to bite the bullet and take 4-2-1's.

This workshop have told me they can make the headers in either Stainless or Mild Steel, but they recommend Mild steel, as when it heats up it expands. obviously the differences meaning that the mild steel would have a less chance of cracking, but has anyone got any experience in regards to power etc between the stainless and mild steel??

FYI they never mentioned anything else in the comparision between stainless steel and mild steel. obviously rusting etc are there but im not worried about that, a couple of coatings will fix that.

Cheers guys,

Chris

[94dc2tegz]

i talked to some guys b4 at a exhaust shop they basically said that mild steel will last me 2-3 years while stainless steel is double so obviously there are benefits there but i duno.. thats just what he said.

as for ur 4-1's. whats wrong with 4-2-1? I'd prefer the 4-2-1 IMO cuz for a street car all u need is the low and mid increase. whats the point of sacrificing ur mids to get top end wen u can't use it? but thats just me.

plus 4-1 drop lower to the groud - just another thought to keep in mind.

gL.

[LUD35]

thanks for the reply, 4-1 is a performance choice, i can't justify losing top end for low-mid end with my k24. already it makes wayy to much down low to control, i would rather have that power avail to me up top. secondly, looking at most of the k swaps/tuning company cars in Japan, seems like they all run 4-1's with their k24 packages for race reasons again, from what i have seen.

im really only putting this thread up to see what the "performance" differences between the 2 would be, there are many threads on this forum about the other differences.

[EG5]

I havent tested 4-1 set up yet on my EGK20A or EGK24A . With 4-2-1 Headers both cars are running numbers.

Alot of those 9-10 second ALLMOTOR FWD Honda drag cars in Usa are running 4-1 headers and thats because they dont care much about low end power as the car doesnt get driven on the street.

[DLO01]

What insulates heat better? Stainless or Mild?

I am thinking Stainless. But how thick is the Stainless compared to the Mild pipe?

Hot air is less dense therefore lighter and is the better way to expel gasses. We are picking at grains now, but something to consider anyway.

[Drew]

You are well and truly splitting hairs if you are looking for power gains between mild and stainless...

I mean the difference would be like 1/10000th of a kw

[JohnL]

What insulates heat better? Stainless or Mild?
We are picking at grains now, but something to consider anyway.

Any difference in thermal conductivity between SS and MS will be miniscule and of no consequence. If you're worried about this then you should also be worried that SS tends to be polished whereas MS typically isn't, and a polished surface radiates less heat than an unpolished surface because at a microspcopic level a polished surface has less surface area from which to radiate heat.

Given two otherwise identical headers, one made from SS and the other from MS, I'd be very surprised if there were a significant measurable difference in power between them. Having said that, I can't recall ever seeing a SS exhaust on a serious racing car, but I'll bet this is more for the reason that MS is far less prone to fatigue cracking than SS is.

I once had an old VK Commodire (the last with a Holden built straight six) that came with factory MS extractors (the fuel injected model). That car was nearly twenty years old and the extractors were in great condition. SS has a different resonace than MS, and to my ear can sound a little 'tinny' in some exhaust applications.

[Limbo]

stainless is brittle, when compared to mild steel.
When you heat up SS it expands but then cracks under extreme heat.
Mild will expand before cracking. Stainless is stronger

Stainless is stronger but alot of headers are not build with thick stainless as it is expensive.

Turbo headers, all custom ones are made from steam pipe, a form of mild steel which is thicker.

In terms of performance there is no reall difference except that stainless headers are lighter as they do not need as much thickness to get the same strength.

The 'tinny' sound you get is due to the thin SS they used, mild steel as it is thicker, does not make this noise. You can get rid of some of the tinny noise if you wrap them with thermal wrap or ceramic coat them

[SeverAMV]

stainless is brittle, when compared to mild steel.
When you heat up SS it expands but then cracks under extreme heat.
Mild will expand before cracking. Stainless is stronger

Stainless is stronger but alot of headers are not build with thick stainless as it is expensive.

Turbo headers, all custom ones are made from steam pipe, a form of mild steel which is thicker.

In terms of performance there is no reall difference except that stainless headers are lighter as they do not need as much thickness to get the same strength.

The 'tinny' sound you get is due to the thin SS they used, mild steel as it is thicker, does not make this noise. You can get rid of some of the tinny noise if you wrap them with thermal wrap or ceramic coat them

we are talking about small motors tho so the heat isnt too bad. for me, i just couldnt justify spending $400AU on mild steel 4-2-1 extractors when i could get stainless steel 4-2-1 extractors of the same design from megan racing america for $17 + shipping. for me, it was about bang per buck, and the power increase wasnt too bad so it was worth it.

as with the science side of things, expansion is good for durability, but it will probably have problems maintaining its shape for a long time. when it rains, you'll get water splashing onto your extractors from underneath your car, so it will expand, then rapid contract and then rapid expand again. altho its possible for stainless to crack under these circumstances, stainless steel of the same thickness as mild steel seems to be more durable, plus mild steel extractors would deform under these conditions at a much faster rate, which can cause a drop in power if you're chasing kw. so if you can find cheap good ones, then go for it.

[dsp26]

^^^agree with the bang for buck, i too got some random SS 4-1 from the states, works fine for me with supporting mods such as heat wrap, heat wrapped metal cat. despite myself not having the ability or proper knowledge to calculate optimum primary lengths and size, i was merely after the 2.5in collector for my big cam build, besides the primaries were pretty big. only problem was that 4-1s sit too low and i had to spend extra to raise my car (poorly planned)


i would go mild steel and heat wrap... (although i have SS 4-1 and heat wrapped)

either way when you get it done, make sure they implement flex bellows or donut joints.

there would be no performance difference from insulation between materials, heat wrapping is the only benefit as it keeps the heat inside therefore exhaust flow stays fast and exhaust vacuum or "scavenging effect" is increased or maintained at the very least. this also serves to make aftermarket metal cats work more effectively as they get to a more optimum temp to catalise properly...
this is more effective compared to HPC as it retains more heat, i can prove this to you when i can actually hold my primaries after a hard drive for about 2secs.

anyone familiar with "Moh's Hardness scale" from yr8 science? softer items tend to flex before cracking/shattering whereas the other end like 10 (Diamond) would just shatter...

SS is technically stronger but because it's denser, it expands less and it would crack easier especially at the welds if you don't have a flex system or if you heat wrap too tight. same reason those mountain climbing/abseiling hook thingies get thrown out if you drop them... coz their so dense

in terms of actual performance from the headers alone, i'm assuming the place making this custom setup for you would either:
- have a standard design template
or
- can make it tuned length to your powerband desires

if its the former option you may as well get a proven off the shelf item.

the reason theres a powerband difference between 4-2-1 and 4-1 is because of the lengths of the primaries being different obviously from design concept.

although theres a certain flow on headers/extractors, slightly more backpressure is achieved during the 4-2 phase compared to 4-1 as the 1 is USUALLY a 2.5in collector to aid in top end flow. I don't know of any 4-2-1 headers with a 2.5in collector.

[94vtirozguy]

if heat insulating is what you are looking for, you can get your headers coated by someone like HPC, and there are some other places that do it as well.

[dsp26]

As I said above, heat coating is crap compared to heat wrapping

This is my challenge to anyone with HPC... go for a hard drive and tell me if you can hold your primaries after with your bare hands

of all mods you do to a car HPC is THE WORST bang for buck... it's even worse than spending $10 on rare earth magnets or a hiclone

Reason some hipo cars and workshop use them is because they have free or easy access to it when it flakes.

only downfall of heatwrap is:
- if you dont clamp them properly or if the bends on your extractors hit the ground they rip
- if your car is too low and/or you don't have splash guards they will take in water. mine was about 5cm from the ground at one stage, during heavy rain my car was steaming. this is bad if you have SS headers, but either way who HPC's SS headers?? defeats the purpose....