It'll be fine breaking it in with this pipe...Any pipe is better than none,since all Nitro engines need a certain amount of back-presure to get the engine properly fed with fresh fuel and lubricants...This is really all that is essential to the engine's break in period...But Im sure you prolly knew this anyhow...The hardest part is finding the best tuned pipe for "your engine"...
Im guessing that the old kyosho pipe was made for "small block".12-.15 engines...The problem with average sized "small block"pipes as your kyosho,is that it can be a little restrictive on anything above an .15... Ive spoke with a Team Orion tech.,and he said that one of the best possible matchs for their,and other .18 engines,is the blue GT pipe...Im not sure which ST you have,so Im just pointing a few things out...Another great pipe is the Team Losi "Adam Drake" tuned pipe...It flows great aswell and will keep your nitro engines heat down since it greatly reduces restriction aswell.... <STAY AWAY FROM ADJUSTABLE> tune pipes,like a "CVEC" unless ofcorse you are a long time profesional in Nitro engines with loads of knowledge about exhaust timeing,or if you have a Nitro engine dyno,which not many do!..They are also heavier due to center cones,ect.....More hassel than they are worth,NO PROs run these pipes,not to menchen the expence of these types of pipes is rediculous...Having said this,Im not sure if you have a rear exhaust or side exhaust engine,but Im going to step out on a limb and asume its the more popular rear exhaust,but regardless I'll point the highly recomended GT pipe,and the Losi "drake"pipe out for you>...Just look at em both,one of them will work regarless of your ST type,hence you do a little modifying of pipe hanger...Have fun and happy driving! .....>

Team Associated "Natural,Blue,Black" GT tuned pipe Part # ASC1774 $31.99
Team Associated "GT rear exhaust Manifold> Part # ASC7737 $19.99

Team Losi"Drake"edition hard anodized tuned pipe Part # LOSA9332 $26.55
Team Losi"Drake"rear exhaust manifold> Part # LOSA9347 $18.50