derbi porting and pipe


the derbi was doing solid mid-upper 30s with just the tjt. when i put the bored out intake and 15 sha on i got negligible gains, so it was time to unlock some more power. first step was to take the cylinder off and see what kind of porting potential it had.

nice big transfers

impressive for stock

21mm stock exhaust port

off the bat i took things slow and decided to just raise the exhaust port 1mm. blue line is where i took it to.

i also tapered the exhaust to 24mm. it gave me a slight boost, but there was still a lot of untapped potential. time for a pipe. i didn’t feel like waiting for shipping or spending a bunch of money. time for a hack n’ weld.

i had a couple pipes available to weld to my stock header. nate’s biturbo 2, and zack’s leo vince scooter pipe. the leo vince has a MASSIVE chamber and is a really low hitting pipe. the BT2 is higher end pipe that loves winding out. given the low end luxuries of the variator world i went with the BT2.

welding time

it bolted up really nicely with pedal clearance. i found a nasty pitbike silencer no one else wanted and was in business.

only thing left was a mounting bracket. zack had a moment of bandit brilliance and grabbed a 14mm wrench off the wall…

that brought me up to ~42. i’m still pushing (mostly to try and keep up with/beat nate’s 50cc variated pacer) for more. my condenser took a huge dump on me on sunday, so i just ordered up the derbi cdi benji has. i’m really curious to see what that does.

i’m also looking for more porting opportunities. any suggestions? maybe the top transfer bridge?


5 Responses to “derbi porting and pipe”

  1. This is why I love the Bandits.

  2. 2 john

    Nice job.

    Did you notice any lowend loss with raising the exhaust port? Is your low end killer right now?

    Definitely take out that bridge on the top transfer. I can’t remember where the ring ends are on derbis but I’m pretty sure there arn’t there, so nothing to lose by doing that.

    Also you shouldn’t hit the ring ends if you widen the exhaust window either right? Why not try 1mm more there too.

  3. 3 john

    Oh, and PS. isn’t the header on the stock derbi pipe really small? is it the 24mm you ramped the outlet too? might see some gains with a real biturbo sized header

    • 4 gabeb

      good stuff. you’re right about the ring gaps and top transfer bridge. i have to measure the openings on the bore side and see if they match the case transfer. if they do there’s not that much to be gained without opening up the case transfer there.

      the stock header is 21mm, i could probably pick some up by bending a stock tomos or boss header to fit. plans for down the road.

      i didn’t notice a loss in bottom end from porting, it’s still a ripper off the line.

  4. 5 john

    slippin son, do a write up on your za50 cdi on a derbiiii

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