So fuck the cheaper exhausts/ lets mod some other!

so according to the responses from the post I made about that leovinci cobra stock replica, the thing is a total piece of shit. now my thought was that, in response to somebody's post on that thread about chopping the inside, that you could possibly get some gain from chopping the tube, and letting the faux expansion on there give you some expansion... Steve says that it's probably not even engineered to give any performance advantages, but wouldn't the fact that the chamber's expansion is larger than the stock pipe when you chop the inner tube give you a greater back pressure?

Anyways, fuck that pipe, I'm going to try to chop it and ride it and see what happens. My other question is:

has anyone ever chopped a moby stockpipe at the header and welded a YZ80 expansion chamber pipe on to it? I know some folks who have done it on a puch, but I'm not sure if it will clear the variation of the engine on a moby. I'd like to try to get a list of pipes and mods that could save you a lot of money on all these fucking performance pipes while giving you some performance increase. It would be nice to find good small dirt bike pipes that are selling for like 50 bucks or less on ebay to chop and weld on to the moby header, saving a lot of people a lot of money....

Re: So fuck the cheaper exhausts/ lets mod some ot

haha first mistake, never reference me as a credible source of moped knowledge.

secondly, id replace _probably_ with _possibly_. I cant say for sure whether or not it would be any good.

i know paul has had luck welding some crazy pipe up for his poor man's fast moby, id ask him about it. i think he said it was a pocketbike pipe?

Re: So fuck the cheaper exhausts/ lets mod some ot

Seriously, don't waste your time on that pipe, unless you already own it. Steve is right, that pipe was designed to look good, it is not tuned at all for actual function. An expansion chamber exhaust is designed to to a LOT more then just give back pressure. It is tuned to reflect the exhaust pulses from the motor back at the outgoing exhaust charge with the right timing, the power band of the pipe. The cobra pipe's shape (imagine if it was straightened out) is unlike any other successful moby pipe I have seen, leading me to believe it will not perform well unrestricted.

Re: So fuck the cheaper exhausts/ lets mod some ot

the 'crappy pocketbike pipe' actually does help quite a bit on the top end, i had one on a 45mph stock cylinder puch.

the dirtbike pipes are goign to be tuned for gears, which means they work in a smaller powerband, but hit really hard. Plus most dirt bikes operate in a lower power band (reeds and torque n' stuff), but the kiddie ones might be tuned to be more forgiving. I would avoid anything that is like a 'super pro racer' pipe, and go to stuff meant to give kids a small boost, it will probably have a wider powerband... unless you are riding a moby and want a narrow powerband.

Re: So fuck the cheaper exhausts/ lets mod some ot

SOme times I wonder what would happen if you took the down pipes out from inside two moby blunderbuss style pipes and welded them together. Then youd have divergent and convergent cones and about 20-30 inches total length. I probably would work badly

Re: So fuck the cheaper exhausts/ lets mod some ot

ps, if you can give me your exhaust port open duration in degrees as well as your peak rpms, i can give you the dimensions of an expansion pipe as per specifications of jennings.

i tried it out the other day and made a basic template in Pro/E in which i can enter those two pieces of information and it will return a "properly" dimensioned pipe. i say "properly" because i havent actually built one, but the dimensions are closely based on what jennings describes.

this is a pic of what i came out with. it doesnt look like much, but the dimensions are legit (for my bike) and can be easily adapted for different numbers. i left the header just straight cause god knows how youd want it for a given bike.

i think this could be useful to at least get an idea of the sizes that would work for your bike, then you can go around and look at pocket bike pipes or something and compare them.


Re: So fuck the cheaper exhausts/ lets mod some ot

Wow - good work. Looks long and skinny like a cigar. what was that for?

Re: So fuck the cheaper exhausts/ lets mod some ot

that was for a moby, but that was actually my first try. the tuned length is off, i originally misread the diagram and made the tuned length a little longer than it should be.

so yes, that one is actually a bit long.

i mis-saved the good one but it took about 10 minutes to do after i figured it out, so i can recreate it in less.

Re: So fuck the cheaper exhausts/ lets mod some ot

When you get around to reading Bell, it gives you formulas to calculate pipes with multi-stage headers.

Re: So fuck the cheaper exhausts/ lets mod some ot

mmmm multi stage

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