What is the purpose of using either 304SS or Inconel 625 to make an uppipe? Im assuming that Inconel 625 is also steel?

Cobb is offering both for a Turbo Up pipe but the Inconel 625 is $150 more. Is it worth the extra dinero?

 

inconel is not steel....both 304 SS and inconel are non-farous metal....(no or less iron) meaning they dont rust and wont stick to a magnet.....both are softer than steel and somewhat lighter.

inconel= nickel and copper (more nickel than copper)
stainless steel or cres = steel minus the iron
cuni = copper and nickel (more copper than nickel)

i wouldnt know any difference between the to uppipes. except if one would take heat more. through my experience, i'd say stainless steel would take slightly more heat then inconel would....also SS would look nice and stay nice and shiny....while the inconel would turn a little greenish....hope this helps

-ROB

 

1. So the 304 would be more heat resistant than the 625?
2. The 625 would be lighter than the 304?

 

304ss is a steel and all steel has iron as the main ingredient. in 304ss, chromium, nickel, magnesium, and other metals/nonmetals are added to create a "stainless" steel. it varies depending on the manufacturer and the processes used. but you have to remember, all metals eventually corrode.

inconel 625 on the other hand is classified as a nickel based alloy. its main ingredient is nickel, but it shares similar base metals to steel (including iron). although classified as a non-ferrous metal, it does corrode, but in a different fashion than steels. i'm not sure about the heat conductivity.

i'm not sure about the density of the inconel 625 so i can't compare its weight to 304ss.

hope this helps. i finally had a use for my material science book after college.

 

yes, stainless steel has a very small amount of iron in it....it just depends on how pure it is hence the #s 304, 308, 308L, 309 ,etc. thats why some forks and knifes and such can have magnetic properties and some dont. also, all metal does corrode (incuding aluminum, precious metals such as silver, gold etc. ....its just that some are more resistant than others....hence the name stain-LESS aka (CRES) corrosion RESISTANT steel..... have a nice day

 

oh and i only think that SS would take more heat is because, when you weld inconel, you would use a lower heat setting than SS. meaning the SS melts at higher temp. about 5-10 amps or so. also when you grind on both metals the inconel would be easier to grind. meaning that it is way softer than SS.

would inconel be lighter then SS. not likely...i've held both pipes made of both materials (same size) no noticable difference in wieght.

 

Why would Cobb charge more for Inconel if SS can hold more heat?? Shouldn't it be the other way around? I dunno that's why I'm asking the experts.

 

i don't specifically work hands-on with inconel and ss but i've design things with it. inconel is overall a better material for heat, corrosion, and fatigue & strength at high temperatures.

inconel has a slightly higher density than ss. 0.305 vs 0.285 lb/cu.in.

welding inconel is also slightly different than ss. the welding technique in some cases is harder than ss if a welder is unfamilier with the process.

for $150 i'd say if you want the cool facter and plan to keep your car for years and years get the inconel. if not get the SS and use the money for something else.

 

I do plan on keeping this car for years and i am under the assumption that heat can be a issue with a turbocharged car. So i think i might go for the inconel later. Thanks for all the info guys.

 

inconel is used on the cold side of some turbos, that should be some idication of its ability to handle heat

 

why do you say that inconel is a better material for heat vs SS? when the melting point of SS is about 1420 deg C and inconel is 1350 deg C?



not trying to be an ***, just want to know about the science behind the quote

 

I wondering if inconel has better heat disipation properties than ss. That in itself might be the reason for the available part.

 

if it did cool down faster i wouldnt think it would matter much. considering it's still bolted up to the headers and turbo which would still be extremely hot. i guess it wouldnt hurt to try though.

 

Hehe, im not messing with the engine for a long time. Gonna do suspension first. The car has plenty of power for me right now.

 

okay here’s my non scientific approach to my quote. anyone looking at just melting points in terms of being better is just like saying my car can run 20psi while yours can only 16psi. at 20psi can the car actually handle better at cornering, have a better coeffienet of friction, or have faster 1/4 mile? putting that aside and lets look at other properties of each. SS has a tensile of 85ksi and yield of 35ksi versus inconel with tensile of 140ksi and yield of 77ksi (at room temperature). Inconel does show somewhat better strength. Now lets take the scenario to lets say 800 deg C, way below both metal's melting point, but average for a car. (just incase you haven’t seen any plotted graphs of Temp vs strength for each metal. as temperature increases strength decrease and it isn't proportionally) SS is around 30ksi while inconel is around 115ksi showing a significant difference now. SS tensile and yeild drops of significantly around 760 deg C. so now when your temperatures starts increasing to 870 deg C under boost SS life will drop even more. now moving on to thermal expansion since we are in a higher temperature zone. SS Coefficient of Thermal Expansion is 9.6 and inconel is 5.5. I’m not a metallurgist but i’d say SS does expand somewhat more than inconel and with big temperature changes that tight fitting up-pipe is now becoming a problem. So moving along to this cycling of metals in terms of fatigue. i haven’t seen any real numbers in terms of fatigue but i’ve heard that inconel can withstand much more fatigue cycles than SS especially at high temperatures giving it a longer life at the same loading.

i won’t get into creep but it’s deformation that occurs over period of time when a material is subjected to constant stress at a constant temperature and inconel wins.

and I won’t get into scaling with is the resistance to corrosion by air at elevated temperatures and I’m just going to say inconel wins too.

so in general at high temperatures inconel is better.

if i’m generally wrong with my points above can someone please correct me. time for me to get some sleep.