Slant Head vs Straight Head

Discussion in '2-Stroke Engines' started by Kiwi, May 12, 2009.

  1. Kiwi

    Kiwi Member

    Is there a reason to go with one over the other? besides possible fit issues.

  2. pdxrhett

    pdxrhett Member

    from what i've read, slant head has more power though i could be wrong quite easily
  3. cpuaid

    cpuaid Member

    my beach cruiser has a 66CC straight head and my mountain bike has a 49CC slant head. the slant head has more torque and is actually more responsive on the throttle than my 66CC straight head. people that have ridden both of my bikes can't believe the slant head is only a 49CC!
  4. Pablo

    Pablo Motored Bikes Sponsor

    My slant head showed up TODAY!!! Good service.

    Unfortunately I'm busy as heck - maybe Friday I'll throw it on. I can tell the mating surface isn't perfect.
  5. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    Hi Pablo
    Does the slant head have a squish band?
    They never show the bottom of the head in pics.

    The Raw / PK 66 cc / "80" does not and it is a very badly designed combustion chamber.
    The Grubee 66 cc does have a squish band and the motor is way
    stronger than PK's right out of the box.
  6. Pablo

    Pablo Motored Bikes Sponsor

    It has a squish band.

    I'm not particular impressed by the cut out near the plug recess. Not sure how the sharp edges will effect combustion. The fins are relatively small as well.
  7. HseLoMein

    HseLoMein Member

    small fins but you get 1 more fin than the stardard fin. I have a slant head and the power is better.
  8. Pablo

    Pablo Motored Bikes Sponsor

    I agree better power, and better power much sooner. (I didn't count the fins!)
  9. HI,

    Sharp edges in the combustion chamber can cause hot spots and detonation of fuel at the "wrong" time....Best to smooth out any rough edges in the combustion chamber.

  10. cpuaid

    cpuaid Member

    nice tip, andy. i never considered it but it makes sense when dealing with slant heads.
  11. Pablo

    Pablo Motored Bikes Sponsor

    Yes I - cleaned the edges up with hand tools. (Small machine and jewelers files). They weren't so much rough as sharp from the angled hole for the spark plug.

    MOTOMTB Member

    Have scoured all the slant head posts, no one mentions how to install the 8mm bolt diam. slanty's onto the 6mm bolt style motors. Obviously it has to sit on there centered. Has anyone done this? Is there a way to center it, perhaps with shims. I really want to try these new slant heads. My motor uses 6mm style cylinder bolts.

    MOTOMTB Member

    Forget it, had a 8mm head bolt setup afterall.
  14. Irish John

    Irish John Guest

    I bought 4 Grubee slant head 66cc kits. They all had a host of things wrong them that the straight head kits didn't. They were definitely not more powerful and absolutely not more responsive. That applies to all four kits. Of the 4 slantheads 3 blew crank seals very quickly (at 90 kms, 119 kms and 247kms and the fourth is showing signs of a blown seal but is now 1500 miles away so I can't inspect it in person).
    All had carb problems with the choke which didn't want to be switched off after starting like the old chokes did (not a good sign). The big problem with the new Grubees was increased compression which was too much for the crank seals. To fix it I had to install thicker head gaskets. The increased compression did NOT increase performance any more than the older engine - in fact the older engine was much less tight and ran a great deal more smoothly with a better throttle response.I will try a Rock Solid kit soon with a slant head and I'm told they aren't problematic) The clutches on the new slant head Grubee kits are so stiff you need to be quite strong to pull the lever in. I( will NOT be buying any more of the Grubee slant head kits that is for sure. The supposed "improvements" are in my experience a giant leap backwards.
    There was a lot of other things about the new kits that I covered in a thread:
  15. goodtime65

    goodtime65 Member

    The slant head realy increases your compresion. I use ZOOM' s engines and at first I blew quite a few of them. 6 in my first year. Between last summer and now I only blew a piston last summer other than that we have all had good luck. And to let you know we are WOT riders and we pound these little motors I rode all winter. What ever engines ZOOM is selling now I dont know " Flying horse " I think . I havent tried one of these yet but next week I will. My bike right now 80 cc zoom motor, 36 tooth sprocket. short expansion chamber and NOS Im not giving up until I can hit 50 Mph

    MOTOMTB Member

    Just installed my slant head, after cleaning up the Combustion chamber casting, plug thread area and adding a heat sink. First impression is wow! Bike idles smoother, less noise, revs smoother, easier to start and a NOTICEABLE increase in torque and pickup through out the range. Really does feel like a different motor, feels and sounds like my old MX race RM80, you can hear and feel the difference, you actually get results relative to how much throttle you turn instead of just a bunch of noise and no "pull". I definately noticed more "PULL" then with stock head and no mods. Didn't have a chance to wind it out so we'll see what top end is like.

    Mind you, it's not quite a controlled test on the slant alone. Some other mods along with the slant were, cleaned all suit and carbon on piston etc. from 1 season of use, mixing oil at 16:1 for a long time. P&P the transfers and exhaust (exhaust is a must!) gasket/manifold matched intake and exhaust(a must do! expect better engine life and performance overall), I also made a custom intake manifold which was matched to the intake.

    Here's the thing, higher compression means more power in the form of torque etc. but also more heat and more force for each "bang" on the con rod, piston and associated bearings. If treated like $hit, WOT etc. I would imagine less life from the components. I'd imagine I've bumped things up to about 3-4HP just from the mods I've done. I don't think the components could take anymore without loosing reliability. Someone needs to design a nice billet case with upgraded crank bearings seats, rod etc. and keep it under 400$CAD (I'm canadian) total kit. That would make that person a stash of cash for sure. Hmmmmmmmmmmm.