I have a 99 prelude with the h23a vtec. The car was stock with the h22b but we but the h23a, blew the h23a and put a new h23a in the car. The car is revving up to 3500 rpm exactly. No matter if I'm in neutral or in gear. I have heard it is the crankshaft sprocket but before I try that, I want to know what you guys think and if that's wrong or I should do something else. Thank you

 

Eh there is no H22B?

Its in limp mode. What codes it throws? What ecu youre using?

 

Typically if theres a problem with the crankshaft position sensor, your going to throw a code.
(TimiK) is right, its in limp mode. There are alot of things that can cause that but regardless there should be a Check Engine Light on and a code stored in the computer.
Start by scanning the ecu for the cel code.