Ramrod90

I am in the very early stages of a sled puller build and I don't want to be limited by rpm. If I have the 4k GSK and the 60lb valve springs, will the motor be safe at 4k rpm without hurting anythig or will I need to do some other mods to the engine. It will be a DD for a while before I get serious with it so I need to know if these are support enough for reliable rpm. Thanks.

Dglass89

4 k should be alright

Ramrod90

alright cool, so the engine could handle it fine but are there any downsides to dd'ing with this kit?

Dinner

There is no bearing squeeze, etc when running a Cummins around 4k?

From everything I've read as long as you have the head looked after you should be good to go. I've never heard anyone having to build up the bottom end for minor sled pulling/dragging mods.

Big Blue24

No downsides to daily driving with 4k springs, just a touchy accelerator pedal; but that can be remedied by adding a heavier throttle linkage return spring.

FYI, you probably wont be able to turn more than 3600 rpm with full fueling with 4k springs. They will free rev to 4100 or so, but most sets start to cut back around 3600. Anyone serious about sled pulling will step up the 5K springs, even if they only run down the track with 4000-4200 rpm.

That said, until you do some head work ie porting, cam, oversized valves, your truck won't make a lot of power above 3500 rpm so 4k springs are perfect for daily driver that sled pulls occasionally.

wvopowered

I had wondered about the safety of running high rpm also. According to http://dodgeram.org/tech/dsl/Facts/94specs.html these engines start to self destrucked above 4000 rpm." * Destructive torsional harmonic resonance occurs at 4100 RPM
* Crank and rods fail at 5400 RPM (if you make it through 4100 RPM)"
But this info my not be correct because a lot of people are running these motors higher than that . Do they balance them ,run a better dampener?

stuckey200224

i wouldent put too much faith in that. i personaly know 3 guys who are running a bone stock cummins bottom end in a unlimited single class and they are all turning at or around 6,000. these engines are tougher than most think gey some good valve springs and maby a dampner and you will be fine as long as the eng is in good shape.