in the process of modifying... i just added a $120 dollar performance hp carburetor kit with velocity stack and uni air filter which went together perfectly with minor machining... so stoked... i also ported and skimmed the cylinder head... again worked out very nicely, especially since my dads got a metal lathe in his garage... also added big nobby off road tires and mud fenders for the off road look...now am waiting for super performance hp expansion chamber exhaust pipe ($109) to come in the mail which will be here in a few days...then i will post pictures and let everyone know how it worked out.
Howdy fellas.. Ive been using expansion chambers for quite a while now.
By changing the header pipe length, )between the flange and the expansion chamber) You can dial in your 2 stroke power band to what ever rpm range you like.
A 2 stoke power band rocks compared to a 4 stroke but is optimum for a vary small rpm range which is why the pros tune a pipe to get the optimal power wheres its most benificial according to what tipe of track there running and their riding style.
Also the length of pipe behind the expansion chamber , known as the stinger can be manipulated real well also.
I'll keep this short and simple .
You'll notice a tuned pipe uses a baffle rather than a muffler or soetimes just a stinger.
Heres what I do.
I know that to have good bottom end, a certain amount of back pressure is needed so I use some regular run of the mill orange house insulation , and wrap it arount the end of the stinger pipe `(that has holes drilled) and put the baffle back over top of the insulation. I wrap it pretty good so thecavity is pretty much full.
This not only gives it a real nice throaty sound but I'd guess up to a 15% exceleration boost.
This would work real well ona shorttrack but unfortunately , this back pressure is going to cost you in the higher rpms where a straight stinger following the chamber will give much better top and speed and higher rpms.
I've ben known to adjust my exhaust back pressure a couple times a day depending on whar I was up to.
Any ways my idea is to make atunedpipe with expansion chamber but add a choke per say behind the exhaust chamger that could be manipulated to breath better as You go throw the rpm range , Even just a gear changer and cable to keep it simple/.
.Imagine a powerband that will take you threw a range of 3000 rpm instead of just 7 or 8'''hundredrpm.
An alternative is to do some testing with a couplesprings and see if you could get this restrictor plate to work automaticaly from the increase/decrease in p[ressure caused from accel'deaccell.v
Haggard
