Engine/Transmission (1998.5 - 2002) What determines or limits your max RPM?

[GOT-Torque]

Someone fill me in here, does the ECM limit the rpm of the engine? Is this done by defueling at a certain rpm( i. e. 3400).



I spoke to someone at a local truck pull this weekend that was running twins (HX40 & HT3B), custom injectors, and meth injection and he said he revs her to 4200 rpm. What must be done to rev a 24 valve engine that high?



Also, why would you want to rev that high? Just for wheel speed? I can't imagine theres much power left up there?



Thanks...

 

[RAMICATOR]

the only way to rev a 24v that high is a blue chip redline box.

 

[Bob Wagner]

the redline box bypasses the ecm, marco has the smarty rpm limit up to 4k

 

[PRout]

So. . at what RPM will pistons start smacking valves?

 

[GOT-Torque]

So the stock ECM pulls fuel to prevent rpms from going above 3400?

 

[JCutter]

the redline box bypasses the ecm, marco has the smarty rpm limit up to 4k

Can you hit 4k with just the smarty or need both?

 

[BennyHL]

So. . at what RPM will pistons start smacking valves?

Hopefully no rpm the cummins can hit cause that'd be some nasty valve float. I don't know for sure, but I do assume the cummins is actually interference??



Revs are limited by the computer. However, I'd guess that theoretical revs is going to be determined by extreme piston speeds and stuff flying apart there or injectors/injection system unable to keep up. I don't know which of those 2 scenarios would come first with a 24 valve. Anyone care to experiment. :-laf

 

[JoshPeters]

I'd have to say Bob hit the nail right on the head with the Redline box and the Smarty.



If I remember right the 24v engines come with 60lb valve springs, so 4k isn't a problem.



JP

 

[Smokey96]

You are correct Josh the 24 valves come stock with 60lb valve springs.

 

[GOT-Torque]

Why would you want to rev that high? Just for wheel speed? I can't imagine theres much power left up there?

 

[zstroken]

Yea they come with 60 lb springs, but they are junky 60lb springs. I know of people with some miles 100K or so that are floating the valves at the 4k mark.

 

[Jetpilot]

The stock springs are good for about 3500 rpm and boost levels of around 40#. We have seen vlave to piston contact with guys running twins at 3400 rpm. As mentioned the OEM springs are junk, if you want to run 4k and upgraded valvespring is a must.



Doug Smith

 

[CSnyder]

The stock springs are good for about 3500 rpm and boost levels of around 40#. We have seen vlave to piston contact with guys running twins at 3400 rpm. As mentioned the OEM springs are junk, if you want to run 4k and upgraded valvespring is a must.



OH NO DON"T SAY THAT! :--)

 

[DAWG-1]

The stock springs are good for about 3500 rpm and boost levels of around 40#. We have seen vlave to piston contact with guys running twins at 3400 rpm. As mentioned the OEM springs are junk, if you want to run 4k and upgraded valvespring is a must.



Doug Smith

This is so true. I had to add aftermarket springs, due to valves lightly touching the pistons all six. The fix on my truck also included a thicker headgasket with the cam I have (PDR), one of the first. Sam

 

[Gary - K7GLD]

I sorta suspect the stock valve springs are designed as they are for a purpose. After all, these trucks weren't built specifically with bombers, drag racers and sledpullers in mind!



Things like lighter valve springs and low-tension piston rings help these engines obtain the long service life they are capable of in stock, normal applications.

 

[ThrottleJockey]

Boy these JEG'S catalog triple valve springs will fill the bill...



332 pounds of seat pressure, almost 1000 pounds of tension.



These things will eat the stock Cummins rocker arms and pushrods



http://www.jegs.com/webapp/wcs/stor...toreId=10001&catalogId=10002&categoryId=17551