Headers: Mild Steel or Stainless

[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.