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-   911 / 930 Turbo & Super Charging Forum (http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/)
-   -   JET HOT 2000 Coatings? (http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/312774-jet-hot-2000-coatings.html)

cgarr 11-02-2006 11:04 AM

If there is only One thing I have learned here that is, that hot air moves faster than cold air.

Craig 930 RS 11-02-2006 11:13 AM

Especially on Pelican ;-)

mb911 11-02-2006 11:17 AM

I am asking about your rotary muffler? Whats up with that?? Pics??

Craig 930 RS 11-02-2006 11:33 AM

;)

http://forums.pelicanparts.com/uploa...1162499551.jpg

http://forums.pelicanparts.com/uploa...1162499571.jpg

mb911 11-02-2006 11:45 AM

so I am bit slow ha!!!!!!!!!!!!!! :D

Craig 930 RS 11-02-2006 11:56 AM

Nah, I just gave it a weird name for fun -

mb911 11-02-2006 12:01 PM

I guess then I have one as well

WydRyd 11-02-2006 02:05 PM

WOW, I'm gone for a few hours and look what I've stired up :D :cool:

ANYWAY, so the general consensus is that, YES, header coatings are worth it and NO, don't coat the inside of the headers!

quattrorunner 11-02-2006 03:25 PM

N/A guys are fine with this(coating inside). Like kevin has said, it needs to be cleaned, degassed, sandblasted and then coated after a final particle removal process. The insides obviously don't get the sandblasting/beadblasting done other than the ends that are reachable by the ends. This is the most important part of the process. The headers that are for N/A cars get the inside as an upgrade or bonus if this is the poilcy of the coater, so they would think they were doing you a favor if it gets done. And the guy coating is probably some guy getting just over minimum wage in some cases, so he may not have the gearhead smarts to figure it all out himself. It's really important that you make it known it should be uncoated. Big red letters on a sticker on the part when you ship it. If it were possable to sandblast the inside of the part, I think the flaking issue would be solved. The coating does keep the part cooler on the outside in comparison to no coating, and would be even cooler if it were coaten inside as well.

Craig 930 RS 11-02-2006 03:54 PM

Wyd - Ah the internet - we on Pelican are contentious on everything aren't we? :cool:

Still not sure if I personally see the benefit/risk ratio as being in my favor, but that option is one some may want to use.

quattrorunner 11-02-2006 03:57 PM

It is for those that want to outrun the other person at all expense. And I personally think it looks cool in white or light grey.

Randy Blaylock 11-02-2006 04:38 PM

If you coat your common lower price point aftermarket stainless headers, and ever have a crack (and it's when, not if) that needs repair, sorry charlie....

It's simply not possible to debride the base metal of the coating media thoroughly enough to get a weld of a character and quality that's worth doing, it's new header time.

The cost vs. benefit relationship doesn't pencil out to me.

On the subject of headers, perhaps Kevin will weigh in with his experience on a realistic service life of the garden variety headers from B & B and GHL, vs. other custom headers fabricated with superior alloys, or even inconel.

quattrorunner 11-02-2006 04:54 PM

The reason for the stress cracks is what? Heat cycling I guess.(I'm not sure) The reason for the coating is to keep the heat away from the header (or at least inside the tubes) The exhaust keeps the heat and not the headers in theory. So I would think that this coated header will outlast the uncoated part because it keeps it cooler. This is the selling point that coating companies sell. I used to work for one.

Randy Blaylock 11-02-2006 05:06 PM

Perhaps if the interior of the tubes was coated comprehensively, but as has been noted it's virtually impossible to prep the surface correctly, so the coating process will be inconsistent, and likely incomplete.

Given the advisory, in this particular application, to NOT coat the inside of the tubes, because of FOD concerns, the coating on the outside will only contain the heat inside the tubes, with no protective quality for the base material.

I'd hazard a guess that only coating the outside, while probably showing some benefit with regards to exhaust gas velocity and energy transfer which will reduce lag, and lower ambient temps proximal to the hardware, will also cause the headers to act as more of a heat sink since the external coating will not allow the heat to escape as readily to atmosphere through convection. I don't know what effect this will have on material life, but my gut suggests that it's probably not beneficial.

Not to mention the inability to make repairs.

I have been wrong before though....

quattrorunner 11-02-2006 05:23 PM

You may be right, I just don't know. My guess is that it would be better than nothing to have the outer coated but not the inner.

Ken911 11-03-2006 12:18 AM

Part of the reason stainless steel headers crack is from Chloride stress cracking corrosion. They will all crack due to this just some sooner that others even inconel will crack from it. The stress from heat distortion, the heat itself and the exposure to chlorides (road salt dirty rainwater etc.) will cause this type of corrosion. It is not notcible like general or pitting corrosion the metal will just crack at a high stress point. If these headers are new before they are coated IE never been exposed to rain water and road salt. then the coating should prevent or at least prolong the time until the headers crack.

mb911 11-03-2006 02:43 AM

typical cracking of stainless is caused be overzelous welders welding to hot causing carbide parcipitation which in turn will crack over a short term or long term depending on how hot it was. Not toot my own horn by I teach metal science and welding along with being a CWI so now I do have more experience with this then the average internet guy:D

Ps Not being a jerk or anything but who is kevin???

Jim2 11-03-2006 06:42 AM

Over and above what Ben said, the headers we use don't have sufficient expansion points to allow for material growth at operating temperatures. By comparison aviation exhaust systems have bellows or slip-joints at most multi tube unions or collectors. Our header tubes are welded to the collectors, and have minimal usage of expansion joints. Too many rigid mounting points as well.

From room temp to 1600F, 12" of stainless tube can grow upwards of 1/16" and is subject to continuious variations from 900F at idle to 1300F cruise, to 1600F on boost, so the header temps are changing constantly while driving, as a result they continously change shape to a minor degree, and if there are limited expansion points, they eventually develop cracks.

On a different note, some advertisments I read claim to have turbo headers made from "aviation grade 304 stainless". 304 is not (never) used for comercial aviation exhaust. I guess the statement helps sell product. Aviation is 321, it demands a price premium because thin wall 321 tube only seems to be used... in aviaiton exhausts.

Zeroclearance 11-04-2006 08:43 AM

mb911, you can always do a search..

Home of the K27 HyFlow...

rsrfan 11-04-2006 08:53 AM

Ben,
Kevein is Kevin Matwichuk of Ultimatemotorwerks, http://www.ultimatemotorwerks.com/ . Kevin is THE Porsche turbo guru on Rennlist and many other forums. Kevin is responsible for creating new variants of the venerable KKK turbo chargers with new castings and CNC millwork. The k27 "s" and k27 "HFS" variants are his. He is also responsible for the "zero clearance" process used on Craig's beast. He is truly accessible and will talk with you for hours on your turbo specific needs. He is one of the good guys.

JP


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