On the CFM56-7B-26K you'll get roughly; 1st detent 45%, 2nd detent 70%, full reverse 82%. More interestingly, these reverse N1 figures equate to around 50% reverse thrust of what you can expect of same N1 with "forward" thrust. This varies with speed. The higher the speed, the more efficient the reversers work. At lower speeds the brakes will be far more efficient.
I'd like to add the misconception of pulling hard will give you more reverse and also faster. There's a mechanical lock which prevents deployment above 10' RA, and at touch down you'll first get idle reverse then after successful deployment you may increase all the way to full reverse. Some guys keep pulling the levers till they get their desired reverse. This is not only wrong but may cause damage to the levers. Pull once and deploy them, wait for two seconds with a slight pull and they will click out of the detent at the earliest opportunity.
Last edited by RYR-738-JOCKEY; 13th Dec 2008 at 01:16.