thank you all for the quick responses. I'm not 100% convinced this is the case since I can see nothing physically different with them besides one having a larger diameter but I appreciate the feedback and will see if there is a way I can test this again with a better regulator. Also, as an aside, I was wondering if anyone had any recommendations for flow meters suitable for something like ethanol? It would ideally be something I could read an analog signal off of so that it could be used in my engine control loop. I've been having some difficulty reliably predicting flow rates when using a pressure transducer upstream of the orifice and I wanted to see if others use this same approach or if there is something else more sophisticated? Graham On Saturday, September 13, 2014 5:07 PM, Monroe L. King Jr. <monroe@xxxxxxxxxxxxxxxxxx> wrote: Without the typo orifice geometry is the only answer. Monroe