OK I've been driving around with no speedo for over a year now. Its not needed as long as you know what the rpm's are at the important speeds. This is supposed to be a race car so why does it have a speedo in the first place
The computer gets input from the speedo gear, so when you put in 4.56 gears and the speedo gear is telling the computer that you have 3.55's there are problems, like revving into the rev limiter on every shift.
At least this was my understanding.