Motor Size and Power Comparison

Discussion in '2-Stroke Engines' started by Cali-Rider, Nov 8, 2012.

  1. Cali-Rider

    Cali-Rider Member

    Hello Everyone,

    I was the proud owner of a 66cc motor from Motovelo until I found multiple problems that the company was not willing to fix. I did everything possible to correct the problems, which still ended in failure.

    I went in on a deal with Snarfu (a member here really named Jonas Anderson) to buy 4 Super Rat motors at whole sale price. (Only trusted him since I "knew" him in real life) I was going to sell two of them to cover most of the costs of the two that I would keep. Either way, I never heard a single update on the order in over 4 months after I paid him. So I am ready to accept the fact that I might need to start looking at other options, or give up MB, which isn't going to happen.

    A. 48cc/49cc Slant Head 2.2hp
    B. 66cc Slant Head (GT5) 2.75hp
    C. 66cc? Super Rat 3.0hp​
    1. Are the above numbers accurate for these motors?
    (I found the information on

    The 66cc motor I already owned didn’t fit in my small mountain bike frame as is, so I had to put a slant head on it for clearance reasons.
    I have a picture HERE:

    I hear that the 48/49cc share the same lower end as the 66cc therefore making the 66cc less balanced and adding vibration.

    2. Does the 48/49cc have a noticeable amount less vibration than the 66cc?
    (Does anyone own both to compare?)

    3. Does the 48/49cc have noticeably smaller outside dimensions than the 66cc?
    (Does anyone own both to compare?)

    4. Does the Super Rat have noticeably larger outside dimensions than the 66cc?
    (Does anyone own both to compare?)

    5. Does anyone know how well the Super Rat and the SBP Shift kit work together?

    Thanks for all your knowledge in advance!
    Last edited: Nov 8, 2012

  2. Fabian

    Fabian Well-Known Member

    I think the power figures are wildly over rated, which is much closer to half of the stated output
  3. jaguar

    jaguar Well-Known Member

    bottom ends of the 48cc and 66cc are not the same. But if you get the 48cc you can put a 60cc cylinder on it.
    You can replace the piston wrist pin with a lighter one to bring the balance closer to perfect.
    Looking at the picture I can tell you the header is too long for the pipe to be in sync with the motor. click on my link and read about expansion chamber theory.
  4. Cali-Rider

    Cali-Rider Member

    Actually using your link is what made me choose such a long exhaust set up. Acording to you and your information a longer distance between the piston skirt and the middle of the second cone in the expansion chamber lowers the effective RPM range of the expansion chamber. I did all the math on a few sites and the pipe is still TOO LONG to bring it into a useable RPM range for most MB's. So, if you could shed some light on that it would be great.
  5. jaguar

    jaguar Well-Known Member

    Since you don't know the exhaust gas temperature and probably don't know how to figure what the exhaust and transfer port durations are then all you can do is keep shortening it in one or two inch increments until the powerband or top rpm is what you like.
  6. Cali-Rider

    Cali-Rider Member

    wow... thanks for not answering my origional questions at all for one. Two thanks for trying to belittle me. Three I used all of the formulas from YOUR site for all of my equations, so I wouldn't act so jerky to someone that has tried to promote you and your products. Thanks for nothing...
  7. jaguar

    jaguar Well-Known Member

    sorry man, I guess that did sound "not right" to just lump you in with the rest of the bunch. It's just that it's a bit frustrating to me that almost knows how or cares to know how to figure the port timing. please accept my apology. If you can give me your specs I can help you figure out a good starting length.
    ps- I don't know the answers to 2, 4, and 5. #1 was answered by Fabian. #3- only the cylinder/head are larger for the bigger engine.
  8. Cali-Rider

    Cali-Rider Member

    Thanks, when I get my next motor I will get in contact with you about the port maps and such. Since this one is already toast it would be very pointless to show you my old maps. Which is the point in this thread, which of those motors would suit my needs the best?

    There has to be a few members on here with both motors to compare size... Maybe I need to start searching through builds and ask specific members their oppinion?
  9. jaguar

    jaguar Well-Known Member

    I started with 48cc and finally decided like others have said that there just isn't any substitute for size. That's when I put a 55cc cylinder/piston/head on it. Now I am fudging with a 60cc which surprisingly has less transfer base area than the 55cc. Also it has the narrower bolt spacing on the intake that the 48cc has. I will max it out and then compare the two.
  10. Cali-Rider

    Cali-Rider Member

    Ah, that is good to know!
    Can you compare the outside dimentions of the 48cc and the 60cc? Is it any shorter? (that is what I am mostly after)
  11. jaguar

    jaguar Well-Known Member

    The 60cc is only 1/4" wider from front to back than the 48cc.
  12. Cali-Rider

    Cali-Rider Member

    Thank you!

    I apologize for getting angry before.

    Are they both the same height/length from the bottom of the case to the top of the head?
  13. jaguar

    jaguar Well-Known Member

    the 48cc head is .4" lower. cylinder heights are the same. If I had to I wouldn't hesitate to cut some fins off to make room.
  14. Cali-Rider

    Cali-Rider Member

    Great! So far I am leaning towards the 48cc.

    Do both of your 48 and 60's have slant heads?

    Thanks for the speedy replies!

    Does anyone know about the extra size/power of the Super Rat?
  15. jaguar

    jaguar Well-Known Member

    You could get the 48cc, upgrade to 60cc but keep the head if space is an issue. You'll just have to use a rotary tool to match the case to the transfer ports bottom, and to enlarge the head "dish" to be 45mm wide.
  16. Cali-Rider

    Cali-Rider Member

    That is an interesting idea for another build but since I've already fit a 66cc in here with only minor modifications that would be overkill in my opinion.

    Is there a very noticeable difference in power between the 49cc, the 66cc, and the Super Rat?(Any examples?)

    I know what ever motor I end up with I will enhance for my specific uses, so I am wondering what would be the best starting point?
  17. jaguar

    jaguar Well-Known Member

    the 49cc is just plain gutless. I have no experience with the 66cc but I think my 60cc is similar to it. You'll want to either:
    1) add an intake extension
    2) add a reed valve and expansion chamber (and hopefully cut the baffle and add in a 50mm extension for a mild street powerband)
  18. Cali-Rider

    Cali-Rider Member

    Thanks for the ideas, but I already have most of those implamented on my current dead motor. I am not asking how to increase power, since I've already done lots of reading on the subject.

    I want to know the differences between motors A, B, and C.

    You called the 49cc "gutless" I will assume that means it has far less torque than your "60cc"?
  19. jaguar

    jaguar Well-Known Member

    yeah, well 48cc is 27% smaller than 66cc
  20. Cali-Rider

    Cali-Rider Member

    ok, so far the facts we have are:

    A. 48cc (.4"shorter height, .25" smaller width, and 27% less displacement than the 66cc)
    B. 66cc (Opposite of A)

    Jaguar: Do both of your motors (48&60) have slant heads? Thanks