He only made it to 160 because he was watching an incorrect tach. I don't think he would have a problem getting to 170 because not only do I remember his car being fairly well modified but a magazine article I can't seem to find got 165 out of a stock Z. The fact that this exceeds the 155 mph stock limiter was brought up but I don't think any reason was given. But the point being that in this instance there should have been ample horsepower for the task.