exhaust heat

[jlat]

hello people; What do you think? Does SS kick of more heat than aluminum? It's been hot alot here in Mass. and while driving my car I get hit with these waves of heat (I think is comming from the pipes) that's new to me. Any metalurgists out there?
IBBY

 

[ijames]

Yes. Oh, you want the long answer . The emissivity of aluminum at a few hundred degrees F is about 0.05 to 0.1 depending on surface finish and exact alloy (see METALS/NON-METALS - Emissivity, for example), while mild steel is slightly higher at maybe 0.1 and stainless steel about 0.3 to 0.5ish. The heat power radiated by an object is proportional to the emissivity (and the absolute temperature to the fourth power so a little hotter means a lot more heat radiated). So at the same temperature stainless steel will radiate 3 to 10 times as much heat energy as aluminum. The same formula is used inside those cute infrared thermometers so if you really care about accuracy you need to calibrate the ir thermometer for each surface with a contact measurement, or put a little piece of masking tape on each surface and just look at it with the ir thermometer (they are usually calibrated for an emissivity of 0.95 and that's about what masking tape has). Enough?

 

[Pronto]

Exhaust pipes are not aluminum.

 

[jlat]

hello people; Ijames I do believe you go to the head of the class on that one and Pronto is correct. How about steel. Does SS kick of more heat than regular mandrel bent exhaust pipe steel? And if yes would you say alot more or very little?
thanks
IBBY

 

[ijames]

Actually a lot of the TSO guys are using aluminum downpipes, probably TSM as well. Doesn't matter to me, though, because the OP specifically asked about aluminum vs. stainless, not whether either was actually used. Also, if you look at my post I gave the emissivity of mild steel as maybe 0.1 (actually it can go up to 0.5+ depending on surface finish) so it will give off a little more heat than aluminum but not nearly as much as stainless steel at the same temperature.

Also, starting with a 2.5" diameter downpipe and going to 3" will increase the surface area by 3^2/2.5^2 or 1.44 so it will give off 44% more heat even if the material is the same. Go to 3.5" vs 3" and it will give off another 36% more. I could really tell the difference in underhood temp when I went from a SS 2.5" to 3" dp.

 

[Pronto]

You could be feeling waves of heat from the turbo after going into boost. The other day when it was very hot, I felt pockets of hotter air while riding my motorcycle. Even the pavement was hot on my feet at lights.

 

[Turbo6Smackdown]

I applaud your search for knowledge, but I gotta say it. Unless you're running 8's or lower, I wouldn't worry about it. Say you find the real answer. What are you gonna do about it? What does it affect? If you're running a 160 t-stat, with all the other goodies to keep your engine running cool, what does it matter? Put your efforts into other areas, that will affect you more. Just trying to help.

 

[disco stu]

Good info from ijames and Smackdown.

There is just alot of exhaust on these cars and if the wind blows around and under your car right you will get blast of heat in the face.

I would probably stick to keeping the engine cool and if the underhood temps seem too high to you the best thing to do would be ceramic coating all the exhaust including housing. Make a big difference.

 

[jlat]

hello people; I always thought that SS gave more heat and now I know the answer. I'll put it my memory banks as I think it could be useful someday.
And Disco -Stu is probably correct with the wind blowing in such a way to feel the heat like I did. I'am glad it's under the car. But with DP and pcs. in the engine bay I'll think twice about SS.
IBBY

 

[Little6pack]

You could be feeling waves of heat from the turbo after going into boost. The other day when it was very hot, I felt pockets of hotter air while riding my motorcycle. Even the pavement was hot on my feet at lights.

Nah what you felt was manopause LOL

 

[Turbo6Smackdown]

That's what I did. I had jet hot coat all my stuff in extreme sterling, to keep as much heat out of the bay as possible. I always use stainless when I can, because it's more durable than aluminum When I do something, I want to do it once, and be done with it.