how long is a piece of string ? you need to tell us the contributing perameters ie... Clutch and diff ratio , engine type, pipe, surface driving on, weather conditions, type of fuel and i think thats it.... on average you will find they would hit about 35 to 40 mph with the r21 engine which i think is a 3 or 4 port. but with the right modifications could hit 50 mph or so... hope this helps.