Hmmm interesting idea BUT that pipe is for a 49 CC engine....In order to maximize the performance of the tuned pipe it has to be designed specifically for a particular engine...Has a lot to do with intake / exhaust opening timing , RPM range etc..Still the pipe may be more beneficial than the stock muffler....Looks to need some minor bending and fab work to get it to fit to the Dax engine....If you do it, let me know if it works cause I have the Dax 70 also....FWIW my 70 also does about 27 MPH max on the std 44 T (lotsa Revs!)...If you want more top end a smaller rear sprocket would be the cure although this would lower acceleration and low end pulling power...
i have the 44 tooth but i was doing about 32 out of the box i did the exhaust mod with or with out change the needle position the bike now does 28 and its runnig the same rpm. im mad, but now i can only do 15 cause im pedaling for now cause my throttle cable broke
check the sparkplug and see if the engine is running lean(dry white to grey colour plug =lean) (biscuit brown colour plug =good) (black=rich) you may need a larger main jet or get yours drilled out, i always set cruise with the needle and flatout is set by main jet ,take your time to get optimum results if its too rich it wont revout or if its too lean will rev to the moon but it will cause meltdown of piston ,in between the two is perfection (power and economy) expansion chambers are not the easiest thing to make or design or tune.also the standard air filter may not be the ideal choice to go with the chamber ,inlet and exhaust pulses in the manifold have great bearing on power if you get a larger air-filter and you will have to change the jetting .it sounds like a lot of mucking about but can reap double the horsepower!!
I used the exact same pipe on one of my 48cc builds and it worked just fine. I cut the pipe at chamber and after the bend coming out of head and rewelded.the chamber mounts under the bottom bracket and the muffler exits out by the left axle nut.Would show pictures but don't know how to upload yet. Don't know how it would work on a larger but it has to be better than stock.