NOT SURE OF THE GRAND NATIONALS BUT U CAN GET THE MSD 2 BAR FROM BARNETT FOR LIKE $60. THEY RATE THEIRS OVER ATMOSPHERIC PRESSURE SO THE 2 BAR IS GOOD TO 24.9 PSI I THINK IS WHAT MINE SAID ON THE BOX. IM ACTUALLY TUNING MY CAR WITH CROME AND IN THE PROGRAM I TOLD IT THAT IM RUNNING A 3 BAR AND IT WORKS FINE.