Stock pipe mod

I put together this graphic showing modification of the stock cag pipe. The mod consists of three cuts and welds, removing part of the header and adding belly. The resulting pipe looks much better, how does everyone think it woud perform?

more torque because of the location of the expansion chamber maybe

Thats what im thinking, but i do have a similar pipe, if you enlarged the chamber more, it would be a little bit better.

For Top End Make The Head Pipe As Short As You Can,for Low/mid Range Add About 2 To 2 1/2 Inches Of ''belly'' .

Rewrap The Silencer With Packing Material For The Best Performance.
Good Luck With This Mod (it Work's).

When you cut the pipe open you will see that the header pipe protrudes into the expansion chamber by about 2". This is real bad. Cut it out before your reweld the chamber to the header. Take about 1 1/4" out of the header and add about 2" to the expansion chamber. Fab up a bar for your chamber mount b/c the old one won't line up with the frame. Your newly modded pipe will kill a jetpro or an IP2 both low and top end.

I've been reading up on tuned pipe theory and talking to some people. Adding belly to the pipe should broaden the power band. Shortening the header should add more top end. Sounds like a winner to me. Can braze it or do I need to weld it?

I'd weld it. That chineese metal is crap, it needs to be reinforced as much as possible. Use low heat you don't want to burn the pipe up. If you're worried maybe take it to a muffler shop and pay them like $10 to weld it after you cut it down an sand off the paint.

kill an ip2 pipe please man your killing me you must not have neither 1 of the 2 pipes you mentioned! that stock pipe is shi$ ! good luck with the mods on exhaust though! word of advice do not weld stock pipe braze it welds will not hold up on that cheap as metal!

I have all 3 sitting right here mounted on the bikes. The modified stock one besides being made of cheap metal makes more power on the low than the jetpro and more top end than the IP2! I know I made it myself, I run it myself. The jetpro and the IP2 bikes can't touch my race bike and they both have BBK's installed! Both of those pipes are great pipes, they are made of excelent construction but the modded stock pipe out performs them all around. Ask IP2 he's the one who told me to mod the stock pipe! Welds work fine if you know how to weld! Reinforce all the factory welds and you won't have any problems. If you can't weld very well or know someone who can don't mess with modding the pipe b/c the metal is cheap and you must know what your are doing to make the pipe strong. I have never had a problem with my pipe and I ride it on a rough brick road almost everyday!

i see your from ohio so am i ! I will have to see it to believe it !! i have had many conversations with josh(ip2) in the last year and i highly doubt that the stock pipe modded will turn as many revs as his pipe(unless you modded the stock pipe to the same specs as his) i would like to see some pictures of your modded stock pipe!

Ritchey,

So can considerable gains be had by simply modding the stock pipe as you described? (Of course a ported carb with adjustable main jet would be included.)

Is any cylinder porting required? Or will you get good enough gains with just a simple pipe mod?

Unfortunately I lost the USB cable for my camera so I can't upload the pics I took of my modded pipe. But I do have these pics of a modded stock pipe sent to me by a guy from PBP that I was discussing this with earlier this year. He has also posted them on PBP in this thread: http://www.pocketbikeplanet.com/showthread.php?t=4243 Here is the quote from Josh at IP2 himself! From this thread: http://www.pocketbikeplanet.com/showthread.php?t=1050&highlight=IP2+jetpro

My bike is modded fairly well, all custom work done by myself. The bike performs best with the modded stock pipe. It performs great with the jetpro and the IP2 when tuned to do so, just better with the modded stock. It may or may not work on your setup I dunno. For the cost of modding your pipe($free$) before buying a $120 pipe I think it's worth a try. You don't believe me then don't try it.. I'm just trying to help out and promote experimenting. But hey that's what I like to do and that's why I'm an engineer and others choose not to be.

I am going through with the mod on my pipe. If the mods provide the low-mid boost as mentioned above, it should work very well with my big bore. Shortening the header might add a few rpm's on top too. I am going to hard braze it back together. I'll try to get some photos to post here.

Good luck man! Keep us posted on how it goes.

Hey that bike looks strangely familiar... hmmmm...

I should have taken pictures of it out of the bike but I was too anxious to try it.

The mod worked better than I expected/hoped. When you add to the belly you will be reducing peak horsepower a little but I wanted a wider powerband so it was worth it. Pulls real hard all the way up and doesn't feel twitchy or peaky. We also tried just cutting the header and leaving the chamber alone on another bike. That worked very well too power-wise up top Just not quite as much pull down low. Getting the pipe out of the divergent cone is key. I would weld it as opposed to brazing. Iam working on pushing over the 36mph mark with the stock 6/68 ratio and a bunch of homemade mods. It was 27-28 bone stock. The exhaust mod and carb and cyl porting made the most difference so far. It accelerates waaay faster now. I still have to do something with the reeds/reed cage to make it really sing. Got some .08 feeler guages for reeds in there now, stockers were fluttering in the breeze, hehe.

Do the pipe mod though, you'll like it. Be aware that you may create a lean condition that you'll have to rejet for. Had to drill mine to .73mm.

Hey thanks for backing me up on this Roomtemp. I did my pipe just like we talked about a while ago. I love it. I hope some people will give this mod a try and post their results. And yes it will require you to tune your carb after installing the pipe just like any other pipe installation. Goodluck guys and keep experimenting. Try changing the size of the expansion chamber, widen it, lengthen it, shorten it, see what works for you!

No problem... I love my modded pipe too. I don't have an ip2 to compare it to. So I can't speak to that. I do like the looks of that pipe but I have no desire to spend that much money on a cag. I'd rather have the fun of doing it myself.

I rode a bone stock cag for the first time in a while the other day. Boy was I shocked. I had been just comparing mine to itself. Mod here, a little gain, mod there, a little gain. With the small gains at a time you kind of get used to it.

Then I rode the stocker.... holy keeeerap! it felt slow.... Those little gains DO add up!
Jumped back on mine out of disbelief....weeeeeeeee......
Must be doing something right, hehehe.

I got an old stock pipe that I've cut out about 1" off the header but have done nothing to the chamber. Maybe alittle difference but not much. Hit up hackmunch and maybe he can direct you to the web site the has all the formulas on how to make a pipe for a 2 stroke.....Its more than just cutting and welding, all the sizes make a difference as well. As for welding, have fun melting holes in your pipe (right hackmunch.....lol) braze it like he was saying cause I had to braze his pipe and my own a few times.....pipes broke in different spots the braze always held up.

Well I have a MIG and have never had any problems welding my pipe or others. One of the programs is called JAVAPIPE http://www.mh-aerotools.de/airfoils/javapipe_en.htm, there is a thread about it, do a search. There are hundreds of 2-stroke pipe programs out there you can use. And yes the pipe dimensions have drastic changes to the performance characteristics of the pipe. The dimensions that Roomtemp and I have provided have been calculated to provide the best and broadest powerband from modding the stock pipe. But please feel free to experiment yourselves.

I'm gonna be trying the mod this week with the measurements that were stated in the post earlier. Wish me luck