I don't know if this helps but I just swapped over to a tuned pipe on a 1/10 scale buggy, and the entrence on the tuned pipe is larger then the stockie, the silicone coupler will fit the tuned pipe so therefor therehad tobe a silicone adapter that fit over the stock pipe making it the same diameter as the tunes pipeso it would fitinto the silicone coupler, make sure you have that adapter or it will be loose and then I would also tighten the zip ties if they are still loose

here is a pic of the coupler, adapter, and two zip ties from the Redcat Racing online parts cat.

hope this helps
peace out

edited info,Iagree with the previous posters, get the tuned pipe along with the header, it does help and does make it sounds like a bigger engine giving it that deeper tone.... more HP, always good if accomidated for