Originally Posted by The_Aleman
I had a Grubee GT5 (66CC) with a factory badge stuck on it with date of manufacture that claimed it was 2.75HP @ 5x00 RPM (forget the exact RPM it said).
Might have been about accurate with the stock kit gear it came with. That one had one of the black cat pipes. Seemed to have less power than 2 of the Dax 66 I had.
From my experience, the power varies widely with the bigger chinagirl engines. You might get a crappy one with lots of gear noise that struggles to rev, you might get an eager, quiet engine that runs easily and revs over 7K. Lots of in-between. There's 5 days in a week and only one of em is a Wednesday lol
2.5-3.5HP is about the range I'd guesstimate stock. There is no "standard" because build quality varies so much with them.
IMHO the important thing to consider with the 66 is the torque. They can make great torque without revving high.
For a long time now, it has been said on this forum of the China Girl/HT engines " They are a crap shoot "
I do believe there are some that are coming over now such as the GenIV Dax engines and the GenV (motorbicycleracing) engines which are the same from what I understand, that are better balanced and have better main bearings and lower shimmed con rod bearing, also Fred Chelminski has said that "Silver Jet Engines that Piston bike is selling are very well balanced 38mm stroke engines, he said about the best he has seen out of the box, personally I have two of the Dax GenIV lowers built up and they are really good running engines and the smoothest at high rpms that I have had, 40+ comfortable MPH with both of these engines.
Power with these two engines is great, I have an older who knows what "brand" with the same basic mods to it as my first GenIV Dax build and the dax engine has a noticeable amount more torque and HP, which honestly I think is due to the much better balance of the GenIV Dax lower, higher smoother revs, when I had my Tach on that bike I logged 9,400 RPM with that engine NOT running an expansion pipe and running a well tuned NT carb at 45+ MPH, torque was lacking a little with that exhaust, and now with a small expansion pipe torque is better but top speed has fallen to the 42-43 MPH which I'm OK with since the lower revs will force me to ride a bit slower and maybe make the engine last a bit longer.
Yeah I know I said a lot here, but I said all this to say that, the "crap shoot" phrase still applies to the China Girls in regards to what you will have when you get done with one even with mods and good tuning, but there are some engines we have available lately that offer a nice performance increase mainly due to the better bearings and the better balanced cranks some of them are coming with.