Whats the maximum rpm a mostly stock 12 valve cummins will give you before coming apart?

 

what do you mean by mostly stock?

I leave at 5K every pull and go down the track at 4200 rpm. I would say I have a " mostly stock" truck

 

around 4200 I was told when I asked the diesel shop putting the 4k gsk's in my old truck

 

don't you have to upgrade valve-springs before turning into these high rpms ?

 

Bunch of trucks with good valve springs and a aftermarket balancer turn 5k and live. Id say nothing over 3200 without springs and after 4,000 theres a great deal of bad harmonics when still using the stock balancer, an aftermarket on will limit this.

 

Stock valve springs 3200
60lb valve springs 4200ish
120lb valve springs 5-6k depending on other factors