Modifying stock motobecane cashew pipes

Jonathan Feldman /

Hey how's it goin yall?

I've built multiple different av10s n shit and this time around I was like... man I'm tired. I'd be down to rip a av7 airsal 47mm. Ya know... the kit everyone swears by if you arent tryna go av10 sicko mode.

Anyway so I got my engine built and it's cute n all ( attached a pic for good measure). but I'm kinda stuck on how some of yall are " derestricting " your stock cashew pipes for kits etc. I did a good bit of reading and discovered that there are two main types of cashews. The old style and the new style. On a older rebel moby post he dissects both and states which one he prefers. He said the older style flows better and would be considered an upgrade if you swapped from the newer style. Pics of both of these are attached. The one with the gnarly straw going inside is the newer one.

From my understanding most of the " derestricting " ( for the newer style cashew atleast ) is done by enlarging the holes in the plate that is removed when you dissect your cashew. I'm unable to attach more pics to this post but I'll post a better dissection of the newet cashew after this is finished.

As for the older cashew.. I dont really understand what some of yall are doing to " derestrict " it?

Moral of the story: does anyone have any pro tips when it comes to " derestricting " either of the cashews? Or maybe you feel like one is far superior to the other? Tell meeeeee. I know this is some 2006 moped tech but fuck it. Shits still sick. Holler.

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Re: Modifying stock motobecane cashew pipes

Jonathan Feldman /

Better pic of the newer cashew

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Re: Modifying stock motobecane cashew pipes

Dirty30 Dillon /

Honestly, I'd just chop down the thin exit tube to avoid the two inner baffles. You could also cut it into just between the inner baffles, test, and chop down more if needed.

I think you're going to want to leave at least a couple inches of that exit "stinger" in there for your ears sake.

Re: Modifying stock motobecane cashew pipes

I don't really do much exhaust hacking, but would shortening the header (blue pipe in the diagram) help de-restrict? Like, would it essentially turn the rest of the pipe into an expansion chamber if you cut it right near the flange? I don't know how to calculate the right header length/expansion chamber size though

Re: Modifying stock motobecane cashew pipes

Jonathan Feldman /

> Nick Haber Wrote:

> -------------------------------------------------------

> I don't really do much exhaust hacking, but would shortening the header

> (blue pipe in the diagram) help de-restrict? Like, would it essentially

> turn the rest of the pipe into an expansion chamber if you cut it right

> near the flange? I don't know how to calculate the right header /length/expansion chamber size though

I hear ya, G. I'm not sure that's what people usually do but that would be a interesting science experiment. There's a third moby pipe that isn't really used often but it's like a little can that goes to a maybe.. foot long header. Anyway on a rebel moby post I remember him saying that the only redeeming quality of that style stock exhaust is the potential to hack n weld an actual chamber to the header provided.(edited)

Re: Modifying stock motobecane cashew pipes

Going by the engine pic you are well above stock with the requirement to comply with regulatory noise laws.

Remove the whole backing plate (or ball silencer) make a new backing plate, drill a 11mm hole (starting point for 50cc and 15mm SHA on a ported AV7) and take it for a noise test ride. Slightly ream the 11mm hole and see if there is an improvement (not louder but a bit more balls for acceleration), repeat a couple of times. Should be in the 11-12mm range for the sweet spot on the stock pipe.

For the later pipe, you want to duplicate the backing plate (or modify the original) with your new size exit either angle as original or over top of the header pipe, length inside the exhause needs to be 1/2 way from back to the baffle plate. You need some containment in the exhause.

For earlier pipe you need to do similar with a new backing plate. Because there is no way to give containment though, you need to cap the new piece of exit pipe inside the exhause and piccolo the side of the pipe with a series of small holes, this will diffuse the sound, derestrict and allow some containment.

On the later pipe if you are pissing off the neighbours too much with the added noise you might want to piccolo that exit pipe. Keeping the peace is way better than having ongoing hassles... just saying.

Re: Modifying stock motobecane cashew pipes

Modded cashews with kits are brutally loud.

Re: Modifying stock motobecane cashew pipes

Jonathan Feldman /

Damn. So the modded cashews are loud as fuck? In that case I might just keep my early style cashew unmodded.. I hate a ridiculously loud pipe these days.

Re: Modifying stock motobecane cashew pipes

> Jonathan Feldman Wrote:

> -------------------------------------------------------

> Damn. So the modded cashews are loud as fuck? In that case I might just

> keep my early style cashew unmodded.. I hate a ridiculously loud pipe

> these days.

Any day . ;)

Re: Modifying stock motobecane cashew pipes

Old style isn’t as loud when modded and derestricted as the late style. The bulk head long tube deal is the only sound dampening and with out it you may as well just run it with no end cap. The model 7 pipe is super nice when derestricted.

Re: Modifying stock motobecane cashew pipes

Indeed - but the best stock pipe are the earlier cashews where you can get out the baffles and swiss cheese them as well as the bulkhead for goodly flow and containment... or just remove the bulkhead and baffles completely and hold it together with sheet metal screws.

Then replace the stub exit with 11mm, throw it on your vintage 18240 Motobecane cylinder (pre Oct 64 D or C89 cylinder) and fly.

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> Daniel '' Wrote:

> -------------------------------------------------------

> Old style isn’t as loud when modded and derestricted as the late style.

> The bulk head long tube deal is the only sound dampening and with out it

> you may as well just run it with no end cap. The model 7 pipe is super

> nice when derestricted.

Re: Modifying stock motobecane cashew pipes

For a 70cc kit with 15 SHA, I went with a 13mm ID aluminum pipe from eBay.

Compared to stock:

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Opened the cap, JB welded the new bent pipe into position.

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Drilled out the center holes to 19mm with a step bit and expanded the side holes.

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I can still piccolo if needed. Thank you Rebel Moby for all your suggestions on sizing this here and other threads.

Re: Modifying stock motobecane cashew pipes

Brandon Weiss (Detective brandon to you) /

that jb weld probably won't hold long

Re: Modifying stock motobecane cashew pipes

from vibration? Suppose to be good to 500F and there is no stress there, the pipe/stinger just passes thru the endcap.(edited)

Re: Modifying stock motobecane cashew pipes

Brandon Weiss (Detective brandon to you) /

> Mike L Wrote:

> -------------------------------------------------------

> from vibration? Suppose to be good to 500F and there is no stress

> there, the pipe/stinger just passes thru the endcap.

The, heat, oil, and vibration. Its a nasty environment inside a 2 stroke pipe. Maybe if it was on the outside of the pipe? But being inside being blasted by the hot exhaust gasses directly may prove too much for it

Re: Modifying stock motobecane cashew pipes

Looks sexi - I would suggest the JB Weld is goodly for shake down of the new pipe but stop by joe the welder and get them to run a bead around that asap

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