I wouldnt powder coat mag wheels. You cant see any cracks if they develop under the powder coating. Paint them using the least number of coat you can this way you can see hair line cracks in the paint where the wheels are starting to break. lol I kid you not!

I know magteks dont have that much mag content in them but i still perfer paint. Ive had 2 dymags crack on me and both times its been the paint thats given it away.

If you really want to powder coat them then take them somewhere that can x-ray them or use a crack detecting sprays before they are sent off and recheck them every year or so. Having them bead blasted also makes it harder to crack detect.

Hope that helps
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If I have to take the carbs off once more...