What is top RPM of Hua Sheng?

Discussion in '4-Stroke Engines' started by mmachine, Aug 20, 2009.

  1. mmachine

    mmachine Member

    Only have about 5 hours on my HS motor but had to try for top speed
    just out of curiosity and it topped out at 34.

    My gearbox is 3.2:1
    Output gear 12
    Rear sprocket 56

    According to the ratio calculator 14.93:1 is the final ratio and top
    speed anticipated @8000 rpm is 41mph.

    But, topping out at 34 caps my rpms at 6600. Really need a tac to
    see what is actually happening but had to ask.

  2. mmachine

    mmachine Member

    yea it was a stupid question

    Even though I asked a stupid question it took me a couple days to find it
    on my own (in spare time, didn't slave it for 48 hrs ya know).

    The little book that comes with the motor states 8500rpm and Googleing
    got me a couple posts stateing over 7000. The site search got me nothing.

    Anyway have a tac on the way to see what's really going on.
  3. clay

    clay Member

    i have never seen a stock bike do 34mph. maybe 24mph.
  4. mmachine

    mmachine Member

    what's a stock bike


    Please define for me what a stock bike is.
  5. jared8783

    jared8783 Member

    my gxh50 with firebelly's combo does about 35-40 on flat land

    with no engine mods and a 44 tooth rear

    And I do beleive that the hs is 7000
    And the gxh50 is 7800
  6. Mountainman

    Mountainman Active Member

    way to break that baby in
    will be interesting to see how well it holds up for you
    thinking that the rings may have already lost a little of slide to the sleve ??

    ride the heck out of that THING
  7. Old Bob

    Old Bob Member

    One thing you need to consider when doing these calculations is to use the rolling radius of the loaded tire not the diameter of it, if the load compresses the tire by 1/2" your calculations could be off almost 500 engine revolutions per mile.

    Although these engines rev to a certain point, look at the torque curve, its well below peak at these rated top rpm levels. To run the engine at this rpm, you need to reduce the load on the engine,which usually involves gearing down and reduces your ground speed while increasing the engine speed.
    If you have a graph with a torque curve for the engine, the rpm you are pulling now on flat level ground will give you an idea of the torque required to maintain that speed. X lbs. ft @ 6600 rpm for example. To use higher rpm with out gearing down you will have to increase the engine torque to at least the level at 6600 rpm. Or reduce rolling resistance, aero drag and mechanical losses.
  8. Irish John

    Irish John Guest

    The only way you can get this speed from a HuaSheng is to use a very small rear sprocket. With a 44T I hit 40 mph on the flat but it couldn't climb any hill and a headwind would stop you in your tracks. It isn't possible to get 41 mph from a HS unless you don't mind pushing the bike up hills. Ipso facto.
  9. Irish John

    Irish John Guest

    The Honda has more power than the HS that's for sure. I doubt a 44T would suit it though unless you live on fairly flat country. It likes the 48T though and sings along nicely at 33 mph and a bit more on a cold night cos it likes the dense air in the carby. Crouched over the tank I was once able to reach 40 mph but the motor wouldn't take that abuse for too long. It's worth balancing the wheels and having the hub bearings really nicely greased and getting the chain & motor position set up perfectly to get the best cruising speed possible. Losing 20 kilos helps as well!
  10. mmachine

    mmachine Member


    Ride it like you stole it!

    Where I live your either going uphill or downhill. The spot where speed test
    done is flat though.

    I did climb a short hill perhaps 600' long at 20mph and pedalling all they way.
    Very impressive considering that I hit the bottom at about 16mph.

    So if wondering why the need for speed there are a couple streets that
    require 30mph if you don't want to end up under the tires of a cager. Was
    just hoping there was more top end so that when going 30 it wasn't winding
    out. Tach arrives on Tues.
  11. Irish John

    Irish John Guest

    You'll know what the right sprocket combination is for your bike soon enough. I'd like to see pictures of it. Have you posted any pics anywhere mmachine?
  12. mmachine

    mmachine Member

    In my last post talk of a 600' hill but left out the word STEEP, the hill was
    VERY steep. I should post a pic of that!

    The bike is average so didn't do the 1st build post. Also it hasn't been made
    pretty yet because not sure if a friend is going to buy it and not wanting to
    put even more hours into it if he is. Might put up a pic tommorrow.

    Friend rode it today and grinning from ear to ear. He said there has to be a
    market for these just let people take a ride. My comeback was the perception
    of price put out by $100 HT kit promos. Unless people understand the long
    term value of these 4 strokes they won't pay the extra price we ask. Curious
    what experience others have had building and selling 4 stroke bikes. I have
    no interest in the 2 strokes.

    Not trying to be offensive toward HT's it's just different strokes for different
    Last edited: Aug 24, 2009
  13. mmachine

    mmachine Member

    the bike in question

    Irish John

    Here's a pic of the boring to look at but super fun to ride bike, my 1st build.
    Still waiting on that tach.

    Attached Files:

  14. mmachine

    mmachine Member

    got the tach

    Tach finally arrived and my bike's setup is matching the gear ratio calculator
    exactly. Just brought it up to 32mph with the tach at 6240 but it doesn't
    want to go much more than that.
  15. Irish John

    Irish John Guest

    Is that a 56T sprocket on the back mmachine? If so have you tried a 48T or maybe a 50T? Nice clean looking build and comfy looking too.
  16. mmachine

    mmachine Member

    Yea John that's a 56t. After posting yesterday a (dim) light went off in my
    head as I realized that my previous speed test was done the a 48t:dunce:

    A 50t would be ideal for me if keeping it but think friend who's twice my
    weight and no need for speed may buy it. With that assumption going to finish
    the bike for him and will post when done.

    Been waiting for a couple months on clamshell adapt for cruiser project. Hope
    it comes soon as that's the build I'm most interested in.
  17. bubbatgs

    bubbatgs Member


    Yes you are correct! The 44 tooth gear on the H.S. is way to tall of a gear. I needed a down hill slope to get into the powerband! After reaching the power band it worked well, But I can't peddle fast enought to get it up to the power band! I did get it to go 49 MPH. I am currently waiting for the 50 tooth rear gear!
    To the orignal poster! Remember when you deal with a centrifical cluch like the one in the Skyhawk transmission, There is an amout of loss due to a slipping cluch! I kind figure it is about ten perscent! (educated guess)
    If you like to run at high RPM, try the long poo poo pipe from www.bicycle-engines.com. It takes a small bit of the low end but at top speed, it works great!
  18. Irish John

    Irish John Guest

    We knew about the 44t being too small way back last year - once you get too small a sprocket everything compounds the problem. The engine struggles at a much higher speed because of it and you can't get pedal cadence easily to assist at that speed. Also a head wind will stop a 44T dead on the Hs. A 50T suits the HS and a 48T suits the Honda on almost all roads but there are very steep hills that the 4 stroke can't cope with no matter what sprocket you use but these hills are not ioften encountered.
    Once the revs are up there should be absolutely no clutch slipping on the centrifugal. That was only a problem we had when we ran the gearboxes wet or had a 44T sprocket or both.
    Regards the long exhaust I have not noticed any power difference between the short or the long exhaust and drilling holes makes no difference to performance but the long exhaust gives a better 4-stroke sound and is a tad louder - it has no baffles in it so that probably explains its louder note.
    Last edited by a moderator: Sep 1, 2009
  19. HoughMade

    HoughMade Guest

    Hey Irish, I'm thinking of going to a 50- as you know, I have the Honda and run a 48. My losing just a touch of top speed doesn't bother me, but I would like a little more torque down low. I'm just wondering if the 2 tooth difference would be noticeable- with this, I am thinking of going with a Manic Mechanic sprocket adapter. Thoughts?
  20. Irish John

    Irish John Guest

    Hi Houghmade, don't know about the Manic Mechanic sprocket adaptor but a 50T isn't hard to find - they come with new G4 Grubee kits. Your top speed will be a tad less and revs a tad higher but you'll get a discernable amount of increased pull low end. It's worth trying and I'm keen to know the result on your GXH50. If you love it I'll probably join you. You'll need a new chain to fit it and if you change chain you might change the drive sprocket for a new one as well. I think you may well like the 50T.