I still have the serial interface and want to upgrade to the usb, and also get a new OS, i have a 402 N/A and want to run an MAF. What is the diff between the 1 bar SD and the 1 bar MAF, and can you just enable the MAF in the 1 bar SD, and where does RTT fit into all this. Sent an email to HPT but didnt get any of my ?'s asked. Also after i spend the money for the RTT, new OS, and new usb EIO cable, would it just be cheaper to buy a new HPT setup?