More on exhausts

[czowner]

I made an interesting discovery at the weekend, I had the front exhaust off to re-paint, (I have been using it in the rain). Just inside the front where the thick flange is attached the welding was very lumpy, blocked about 25% of the pipes diameter, 5 minutes with a rotary cutter fixed that, what an improvement in performance that made.

[red2003]

Could you tell us what specific bike you have? I was wondering if a better exhaust would wake these 200's up a little. I was thinking of bending a custom header pipe on an exhaust machine and bolting up a muffler from like a CRF250 or YZ250F. Sounds like a good Winter project for me. Thanks for the info!!! :D

[Roketarider]

I might take my exhuast off tonight and look into it just for the hell of it. If that is the case, nothing a dremel can't handle!

[czowner]

I dont have a 200, what I have is badged as a Hongdou MD250, the motor is based on the Honda CRF230. Now its broken in Im very happy with the performance, it will easily exceed 70mph and has heaps of low down power. A less restrictive exhaust may be psyological, it sounds more powerful.

Roketarider,
You will need something a bit more heavy duty than a Dremel to clean the weld up.

Jonathan.

[red2003]

Hey guys,

I just won an eBay auction for a complete YZ250F exhaust, header pipe and muffler. When it arrives, I am gonna hack and cut and weld and retrofit it to my Roketa DB07A. That'll DEFINATELY open the exhaust up enough. I'll report on performance once I can get it on the road and check.

[Roketarider]

Hey guys,

I just won an eBay auction for a complete YZ250F exhaust, header pipe and muffler. When it arrives, I am gonna hack and cut and weld and retrofit it to my Roketa DB07A. That'll DEFINATELY open the exhaust up enough. I'll report on performance once I can get it on the road and check.
Look forward to hearing about that.

[red2003]

I may try to do a little exhaust porting while I am right there. Not sure how much can be done with the engine in the chassis, but I will open up whatever I can. Parts should be here mid next week. Next weekend I'll give it a whirl and let you all know what I find out. Should thump pretty good with this setup. Heck even if it doesn't improve HP, it'll sure sound better 8O

[Roketarider]

I may try to do a little exhaust porting while I am right there. Not sure how much can be done with the engine in the chassis, but I will open up whatever I can. Parts should be here mid next week. Next weekend I'll give it a whirl and let you all know what I find out. Should thump pretty good with this setup. Heck even if it doesn't improve HP, it'll sure sound better 8O
I have tomorrow off from work and will be breaking down the exhaust and looking into boring it out. I'm not too worried about bringing out HP in this engine, because, come on, its on 16 hp anyway, haha...I agree, it may sound a little better! I will post pictures of what I do.

[red2003]

Question. How do we post pictures on this board? Do we have to link them to a URL, or is there a better way to post? Thanks for the info guys.

[frostbite]

Register for an account in the image gallery:

http://www.chinariders.net/gallery2

Once you'be been approved (by me) you can then upload images and link them from your posts.

[pobiker]

How much HP do you guesstimate that the pipe retro would produce, and off hand does anyone know what a 250 or 230 CRF puts out compared to the China bikes? I would like to dyno the 250 I am getting, wonder if knobbies will work on a dyno, there is a tech. that builds race engines for H-D's near me called MegaFlow I may have to beg him to do it, he may rip on me for the China bike but all money is green right :lol: hope my bikes are gently floating on a slow boat from China. Just about 20 days till they arrive. How far un-assembled are they when you uncrate them usualy?

[Roketarider]

How much HP do you guesstimate that the pipe retro would produce, and off hand does anyone know what a 250 or 230 CRF puts out compared to the China bikes? I would like to dyno the 250 I am getting, wonder if knobbies will work on a dyno, there is a tech. that builds race engines for H-D's near me called MegaFlow I may have to beg him to do it, he may rip on me for the China bike but all money is green right :lol: hope my bikes are gently floating on a slow boat from China. Just about 20 days till they arrive. How far un-assembled are they when you uncrate them usualy?
They come about 85% assembled.

[red2003]

How much HP do you guesstimate that the pipe retro would produce, and off hand does anyone know what a 250 or 230 CRF puts out compared to the China bikes? I would like to dyno the 250 I am getting, wonder if knobbies will work on a dyno, there is a tech. that builds race engines for H-D's near me called MegaFlow I may have to beg him to do it, he may rip on me for the China bike but all money is green right :lol: hope my bikes are gently floating on a slow boat from China. Just about 20 days till they arrive. How far un-assembled are they when you uncrate them usualy?

Dunno. My RXS200E stock is supposed to make 14.4 HP at 8000 rpm. I think opening up the exhaust should get me to 16 - 17 HP. Should help the entire RPM range, especially on top. A buddy of mine used to race Yammi YZ250F's. I believe his race bike with mild motor work was putting out 32 HP. I think the 450's are pushing over 50 HP, but I am no expert.

[pacman]

Any updates on this?

Is this restriction done so make the bikes are euro2 compliant?

Is a rejetting needed if I do this mod.

Thanks