# What is top RPM of Hua Sheng?

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

1. ### mmachineMember

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

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2. ### mmachineMember

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. ### clayMember

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

4. ### mmachineMember

what's a stock bike

Clay

Please define for me what a stock bike is.

5. ### jared8783Member

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. ### MountainmanActive 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 BobMember

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 JohnGuest

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 JohnGuest

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. ### mmachineMember

MountainMan

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 JohnGuest

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. ### mmachineMember

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
folks.

Last edited: Aug 24, 2009
13. ### mmachineMember

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.

File size:
122.6 KB
Views:
298
14. ### mmachineMember

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 JohnGuest

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. ### mmachineMember

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. ### bubbatgsMember

Weeeeeee.

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 JohnGuest

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