The last few lines of the ad say "This balanced system is not as efficient as the Power... " so even they admit this system is not very good and Paul Dustall was always very optimistic in his power claims.

Jean

jean ,
it's not an ad but a pic out of his catalogue .
The complete sentence is :
"...not as efficient as the Power system on page two but the improvement is still quite marked and worthwhile ."
He refers to his Dr Blair 2-1-2 sytem , for wich he claimed a 10 HP gain : 70 HP (!) at 7000 rpm .
For his balance tube system he does not claim an increase in peak HP , but 5 at 5500 rpm , which implies a substancial increase in torque .
both claims seem pretty wild ...