Engine/Transmission (1998.5 - 2002) 4000 rpm

[tgbol]

Has any body figured out how to increase the RPM on 24v? I would like to increase my top end up to 4000 RPM. TIA

 

[dlange]

blue chip redline box works well

 

[HoleshotHolset]

Is the redline box still 'all or nothing'?



From what I've seen... the RPM will jump from like 2500 to 'Whoa Nelly!' in a split second... when revving 'em up in neutral.



Matt

 

[Jetpilot]

I had the opportunity to ride in a truck that has a Redline and it seemed to work very well. The rpms seemed smooth not jumping around (at least out on the road). The new box allows for you to select the max rpm the engine will spin too. Be aware though that much increase above normal redline rpm will result in valve to piston issues..... I do know where some really good valvetrain components can be purchased from though



Doug

 

[Blacksdieselhp]

So what needs to be done to keep the valves and pistons from clashing? Just bigger springs? Already have titanium retainers.

 

[Jetpilot]

Not necessarily bigger just better and with more seat pressure along with proper bind characteristics. Titanium retainers are nice and help with weight but a spring that actually will get and keep the valve closed under boost is what counts. Heck I surprised more guys running higher boost aren't hitting pistons more often at the stock rpm level.



Doug

 

[dlange]

Jetpilots right. The box is pretty smooth. And you can set the rpm in 100rpm increments from 3400 to 4000.

 

[HoleshotHolset]

Hrmm... the trucks I've seen run with that box were smooth... but the RPM went from normal to obscene in a split second.



Maybe they were early boxes... I dunno.



Matt

 

[Beast2B]

OK, Jetpilot and dlange, what's a safe rpm to raise the rev limit to?

... and to expound, how many hp/torque curves have you seen where the high hp is above 3000rpm? I haven't seen many 500+ curves, but maybe you can point me to some...

 

[Mark_Kendrick]

The question about what RPM is safe depends on boost and drive pressure.



I was told by a head builder that our valves are neutral at 65psi of pressure on the back of the valve. So if you run over 60# of drive or boost you can run into clearance problems at even stock RPM levels.



I didn't observe the measurements but the logic seemed to be right.

 

[Jetpilot]

Beast2B,



The safe limit on our motors is OEM redline @ at normal OEM boost levels... . Once you go above these limits things can and do happen. I have seen valve indents on pistons in trucks turning normal rpm values but running in excess of 60 psi boost. The valvetrain can be made to withstand the increased rpm by using better springs and retainers.



As for the HP curves above 3000... . Well most I have seen do drop off as rpm rises above OEM levels, but a truck could be made to make good HP above this with proper engine work. A good flowing head, a better camshaft, the right timing box, and some good turbos would be required to really make big HP in the upper rpm bands. But for drag racing or pulling the increased rpm would certainly help out on both tracks.



Doug

 

[Beast2B]

Thanks Mark, didn't know you were watching! Is that 65# value based on no backpressure? Like 65# boost will start forcing the valve to open in its seat?



Jetpilot, I kinda expected that from someone... I usually qualify my remarks with that statement! I suppose once you get to that kind of investment and power, you stop sharing the details... I do remember hearing a certain drag racer and a certain sled puller comment that they both launch at 4000rpm!

 

[Mark_Kendrick]

Thanks Mark, didn't know you were watching! Is that 65# value based on no backpressure? Like 65# boost will start forcing the valve to open in its seat?



Jetpilot, I kinda expected that from someone... I usually qualify my remarks with that statement! I suppose once you get to that kind of investment and power, you stop sharing the details... I do remember hearing a certain drag racer and a certain sled puller comment that they both launch at 4000rpm!

~65-70psi of pressure DIFFERENCE will float the valve. this is only going to happen at openning and closing because once the valve opens the pressure should equalize, restoring the valve to normal function.



What will normally happen is dereased performance due to inaccurate valve timing and you may get piston interferance in more extreme cases. the 'mickey mouse ears' are a tell tale sign. the valves are not usually damaged because our valve faces are parallel to the top of the piston. In a severe over-rev and/or over-boost you may hit a valve hard enough to bind and bend it causing it not to seat properly.



they are not usually catastrophic failures meaning the piston is not damaged enough to warrant it's removal. The head is usually repairable(needing some new valves and a valve job).



It's hard to say the exact point at which you need beefier valve springs but on a high HP motor you will normally have the head off for porting anyway... they say an ounce of prevention buys a pound of cure



I'm putting better springs on my rig

 

[PRyker]

Mark,



I am a bit green but wouldn't stiffer valve springs put more wear on the cam lobes and push tubes? Just curious as to what building a high HP truck does to longevity.



Thanks



Phil

 

[Mark_Kendrick]

If ou compare to SB or BB chevy our springs are VERY weak (about 1/2 to 3/4 depending on spec).



An increase from our ~75# seat pressure to ~100# seat pressure would help a lot and SHOULD result in minimally increased wear.



the rings are a much bigger problem in high hp apps... the top of the bore is thoroughly punished above 500hp.

 

[HoleshotHolset]

(I've never pretended to know much of anything about valvetrains... )



Don't we have 60-pound springs? (ISBs have 'em stock and us 12-valvers just need to upgrade the exhaust side)



Matt

 

[Mark_Kendrick]

I was told that the seat pressure on a 24V is 70-75# depending on installed height of the spring.



I've gotten that same # from a from a couple of sources.



I know the 12V is different(60# stock on later models). Because of the height and diameter 12V springs are much easier to replace with better/stiffer pieces. they are closer in size to may gas applications.



My 12v already had aftermarket springs when I got it so I can't say where they came from or what they were set to.

 

[HoleshotHolset]

Gasser parts on a diesel?! Blasphemy!



70-75# is a little heavier than I though they were... interesting.



Matt