High RPM Question

[JoelMartin]

My friend accidentally pulled it in second instead of fourth coming down a hill and his rpm's went to about 3,400 before he realized what was happening. Is that hard on a completely stock truck? It still works fine but was just curious. It is an 04. 5 NV5600 stock truck.

 

[AKaiser]

Yes, but probably not a huge deal if done once and caught. If it's fine now, it will probably be OK. Wouldn't hurt to take a look under the hood while she's running. I've done it a few times, and the truck runs fine. I try to keep it under 3000 when downshifting. Generally, that is easily prevented by not hitting the pedal before 2000 and then, fueling up until it syncs and drop it in, then let off the clutch at whatever RPMs it sync'd at.

 

[rbattelle]

I agree with AKaiser - it shouldn't hurt anything. For example, fast shifts made at or near the redline will tend to "shoot" the engine up past redline (to the 3400-3500 range) when the clutch is depressed in preparation for the next shift. It's not a problem.

Some people say the valves don't start floating until over 4k RPM. I wouldn't worry about it at all.

Ryan

 

[JEstes]

With the upshifting, why wouldn't the ECM defuel as it hit redline?

 

[AKaiser]

It has nothing to do with the ECM or defueling. It's a problem of downshifting into too slow a gear, thus overspeeding the engine.

 

[jmccart]

I was reading a Diesel Power mag swome time ago and these guys made a race motor that went on a dyno over 5000 RPM's. It was interesting that they ran a stock crank/rod set up. I can't remember if the pistons were stock or aftermarket.

 

[JoelMartin]

Does it hurt the clutch or the transmission at all?

 

[jmccart]

Does it hurt the clutch or the transmission at all?

It is probably not great for the clutch, but nothing to worry about at all. It is super hard to hurt that transmission.



No worries.



FYI - There is a thread going on the DTR about which programmers will let you pull to 4000 RPM's.

 

[JoelMartin]

That answers my questions. Thanx!

 

[JEstes]

It has nothing to do with the ECM or defueling. It's a problem of downshifting into too slow a gear, thus overspeeding the engine.

I know that... . I was asking about Ryan's comment about upshifting at redline.

 

[jwilliams3]

Down shifting and going to high rpm with a load works the cam pretty hard however if it only happend once your ok.

Its not the same as taching out just going down the road in a speed situation.

 

[betterthanstock]

My friend accidentally pulled it in second instead of fourth coming down a hill and his rpm's went to about 3,400 before he realized what was happening. Is that hard on a completely stock truck? It still works fine but was just curious. It is an 04. 5 NV5600 stock truck.

The high idle on common rail engines is listed at 3500 rpm. So as long as you don't go past about 36-3700, there is no damage. As the engine gets older, and carbon builds up on the valves, and the springs get weaker, the valves will start floating at lower rpm.

 

[Cattletrkr]

My friend accidentally pulled it in second instead of fourth coming down a hill and his rpm's went to about 3,400 before he realized what was happening. Is that hard on a completely stock truck? It still works fine but was just curious. It is an 04. 5 NV5600 stock truck.

To me all that means is that he should have downshifted sooner as the RPM he would have hit in 4th wouldn't have been high enough. Klenger's handy little spreadsheet only goes to 3300rpm. In 2nd gear, 3300rpm is 25mph and in 4th, 25mph is only 1400rpm. That's assuming 3. 73's.

 

[JoelMartin]

To me all that means is that he should have downshifted sooner as the RPM he would have hit in 4th wouldn't have been high enough. Klenger's handy little spreadsheet only goes to 3300rpm. In 2nd gear, 3300rpm is 25mph and in 4th, 25mph is only 1400rpm. That's assuming 3. 73's.

I don't think he fully engaged the clutch so the rpms could of gone higher. It is 3. 73's.

 

[Cattletrkr]

I would guess that his clutch is nice and smooth now.

 

[johncameron]

Last year when I was dynoing, I hit 3840



I pushed in the clutch before letting off the throttle. My truck is fine

 

[AKaiser]

I know that... . I was asking about Ryan's comment about upshifting at redline.

The most plausible explanation is that diesel engines don't have a throttle, therefore, when you declutch before or right when you let off the fuel when you were in the process of accelerating, the inertia of the engine takes over. There's no mechanism like in a gasoline engine (throttle) to slow it down.

 

[JEstes]

The most plausible explanation is that diesel engines don't have a throttle, therefore, when you declutch before or right when you let off the fuel when you were in the process of accelerating, the inertia of the engine takes over. There's no mechanism like in a gasoline engine (throttle) to slow it down.

Hmm. I never looked at it like that, but that makes sense! Most of my diesel experience has been in marine applications, and some generators, so I've never dealt with declutching one near redline.

 

[rbattelle]

It has nothing to do with the ECM or defueling. It's a problem of downshifting into too slow a gear, thus overspeeding the engine.

I know, I just wanted to point out that 3400 RPM, in-and-of-itself isn't a problem for the engine by citing a situation where the engine will rev that high.



Catteltrkr - you really think that would've glazed the clutch?



Ryan

 

[Cattletrkr]

Catteltrkr - you really think that would've glazed the clutch?

I really have no idea. I just make this stuff up as I go.