if your serious about header wrapping, you should be starting at the headers and working back, all up i used about 4x 50mm thermotec rolls for my entire exhaust system, i also found it much easier (and quicker) to remove the entire exhaust (inc headers) to wrap them tight and neat enough. i also used hose clamps on medium tension to hold the start and finish portions of the wrapping. (makes for easy removal later on).

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Long live the WRC