busting out at high rpms

[sweat90lx]

my friend has an 89 convertible, he just built a motor
it a 393 stroked windsor running a 850 demon carb, msd 6al, and a duraspark distributor, around 5800 rpms it starts busting out
any suggestions on what it could be?

 

[mike93lx]

busting out? what exactly do you mean?

 

[sweat90lx]

almost like hitting the rev limiter