Recently descoverd truck would rev past 3k. I dont know if it has different gov springs. Other people have said that there stock trucks would rev past 3k. I was going down the road the other day, and held in 3rd gear and just kept going up to 3k. I had like 28lbs boost and noticed behind me a HUGE cloud of black smoke. It looked like a black fog bank behind me. Question is, is it harmful to the truck to let it rev that high? I read alot about the 3k and 4k springs. Whats the danger when you rev that high? Valve float? Anything else?<br>I dont want to break my truck doing something stupid with it.

 

3k rpm's for 24 hours straight is ok, but around 3800 rpm's you will snap the stock crank if you substain for longer periods of time. Also stronger valve springs are recommended above about 3600 rpm's.

 

Like CMonroe said...3k ALL DAY...there is a wierd thing at 3800, but most say if you just blow through 3800 to 4200 you will be ok, just don't hold at 3800. Valves &quot;might&quot; float just depends on your motor...mine don't but I am just blowing through the rpm's I don't hold it up there for long.

 

With the heavier valve springs and the 4K governer spring kit, I have run right the the governer cut out(4200 RPMs) a couple of times with no problems. In fact on the dyno in Boise I finially found the top speed of my truck(143)(it gets really floaty above 120). <br><br>My understanding is that it isn't the crankshaft that has problems at higher RPMs it is the camshafts and injection pumps that can be problematic.<br><br>The mighty Cummins actually sounds pretty good at 4000 ;D<br><br>Having the extra RPMs has made my truck alot easier to tow with. The RPMs make up for the gear split between 3rd and 4th....<br>

 

bigbaddiesel:<br><br>My truck is set-up similar to &quot;drawson's.&quot; We have kind<br>of followed a &quot;similar path&quot; in our BOMBING and I can tell<br>you that my truck acts very similar to his as far as the<br>RPM's are concerned. With my Piers 4K springs, I hit about<br>3900 RPM if I hold it and so far no problems! I wouldn't<br>worry about the RPM's on your truck! <br><br>-------<br>John_P

 

cool. Thanks for all the responses. That makes me feel better about revvin' her up a little. I just cant help but grin when i looked back there and saw all the smoke. I'm gonna let er go next time a pass a power joke.<br>

 

Correction I thought that I typed in camshaft but infact I typed in Crank. Sorry the stock low end of these engines are good to over 5000 rpm's. It is the camshaft that can walk from the heliacal cut gears and snap the nose of the cam.