So, does it make sense to ask: at what psi will a K27/6 start to build an unacceptably high backpressure (say anything over 1.5:1), or be outside of it's effeciency range (assuming a 2.5L 951, in good tune with good A/F ratio, high enough octane gas, etc.)? From eclou's post, it sounds like 18 psi may 'generally' be about the K27's limit? I'm sure the K27/6's been pushed past that, but I assume there have been supporting mod's to help keep backpressure/tamperatures down(?).

 

It would useful to know the difference in back pressure at say 18 psi between a K27/6 a LR61 and a Vitesse stage 2. Can this be calculated from known values ( effeciency range etc) or would it need to tested? What are the best ways of reducing back pressure?