Carby Quick question regarding morini's

Discussion in '2-Stroke Engines' started by MOTOMTB, Jul 22, 2011.


    MOTOMTB Member

    Anyone experienced with Morini motors, would they take well to a shift kit? or would it be redundant as they have enough power with the single gear? Looking to do a future build with a morini 6hp or 9.4hp and would like to know.


  2. HeadSmess

    HeadSmess Well-Known Member

    um. a morini is a race specced engine. like, they GET UP AND GO!

    youll snap your chain if you tried a shift kit, if your freewheel doesnt chew itself up first!

    (the power does depend on the exhaust you use though...)

    a stock HT will do 1-1.5 hp. they hold up quite well on a single speed. but they also have a fair bit of bottom end torque. the morini will want to be geared slightly higher, like a 20:1 ratio. it will scream, but my gawd! youll be flying!

    have you ever ridden a ktm50?

    or one of those proper racing pocket rockets? 120km/h on tiny little 8 inch wheels is just insanity...

    freakin awesome :D

    MOTOMTB Member

    Morini and shift kit?

    Just wondering if a shift kit is needed. I know nothing about morini's, how they are geared and their torque specs. I see that pipelyne DH bike just gears them to a single super large sprocket. Not sure how well it climbs under load and how it tops out and uses the available torque. Just wouldd't want to run a shift and figure out it wasn't needed. I'm assuming the pipelyne is geared to climb as it sounds topped out at high speed. Maybe a shift kit would let keep it in a better rev/torque range. If Pipelynes bike does 60ish without a tranny, how fast would it go with a shift kit???? dunno. Anyone?
  4. HeadSmess

    HeadSmess Well-Known Member

    some maths :)

    internal redux is approx 4:1

    10 t sprocket and 44 t chainwheel

    gives about 18:1. thats much the same as a stock ht.

    at 60kmh, a 26" wheel is doing roughly 475rpm

    475*18 = about 8500rpm.

    i believe a morini will spin at 11000 rpm.

    calculate what ratio you will want for say, 70km/h @11grand... it will be around the 20:1, maybe more... doesnt have to be terribly accurate, just an estimate...

    so using either a 24" wheel, or a 52 tooth chainwheel...

    hopefully that would bring the low speed side of things(<30km/h) within the useable rev range...

    once again, it does depend on the exhaust.

    you can have a wide band pipe that produces moderate power,

    or a very peaky pipe that produces a LOT of full tilt. nothing down low. which isnt terribly useful without a gear box.

    id basically start with a 44 tooth chainwheel and experiment with them, as they are fairly simple to change...depending on the mounting methods. bigger will reduce top speed but give more pulling power, and smaller will do the opposite...

    the problem with a shift kit is finding one that will cope with 6 or more horsepower! reliably!

    and personally, at the price they are... just not worth it. the engineering of mounts etc needs to be spot on or youll die...

    MOTOMTB Member

    Right, all that deals with revs but again, it's the torque (pulling power) at certain revs that I'm concerned with. For instance, a bike can have enough power and torque to overcome a crappy low gear set up therefore eliminating the need for a transmission, sort of. With the info above, I think a shift kit would work. The current shift kits could take the load most def just the free-wheel and thinner bike chains being the weak spot, especially the derailleur chain. They would def need replacing often but they can take quite a bit of HP. I was using a bike chain and derailleur set up on a custom build electric bike that could pull 20hp instantaneous torque and weighed about 150lbs sans rider. I'd snap a chain now and then but nothing that wasn't fixable trailside.
  6. loquin

    loquin Active Member

    S6-T is 5.8HP @ 8000 RPM, max RPM is 10K, max torque is @ 7500 RPM.
    S6-S is 9.4HP @ 11000 RPM, max RPM is 13.5K, max torque is @ 10000K RPM

    Ref this thread.
    Last edited: Jul 25, 2011
  7. keatonx

    keatonx Member

    My little brother has a souped up KTM 50(v-force reeds, new expansion chamber, racing carb, tomar racing clutch...), it's sooo fast! I used to have a KTM 65, now I have a KTM 85

    (I just built a weed eater bike that probably has a higher top speed than my bro's ktm 50 on the flats!:tt1:)
    Last edited: Jul 25, 2011