521 Rod length.
 

After having decided to build a 521 stroker i have been looking at stroker kits and noticed that there are two different rod lengths 6.7 and 6.8. i am figuring that there are two different rod lengths maybe for different reasons like compression, engine year, head and valve differences, and use of engine. but im not sure and hope that maybe someone could set me strait on why. and was wondering which one i would need to put in 78 f-250? and which factors will depend on my choice of length?

use the 6.8 on that combo gives the better rod ratio.

ok thanks will do. but just wondering why is it better than 6.7?