What RPM is max for the stock motor

[RHancock]

What RPM is the 5. 9 VE intercooled motor rated for originally by Cummins in stock form?



How much RPM before you need to put the upgraded valve springs in???



What's the max RPM for the VE pump also???



I am looking for rated continuous duty as I have 4. 10 with 265/75's and the motor spins about 3000 going down the highway at 85mph now and I just want to go a little faster.

 

[Bob Beauchaine]

In stock configuration the 1st gen. motors were goverened to about 2450 rpms. Cummins engineers stated you could run all day long against the governor without harming the 5. 9L CTD.



If you are talking about the 60lb springs they are necssary to get maxium back pressure for the exhaust brake and to prevent valve float. I'm not sure at what RPM's you might expect valve float but I don't think that 3000 rpm's will get you there.



With 3. 54's my '93 can run over 100 quite nicely although I usually run at about 70 mph. If you're hauling heavy loads the 4. 10's make sence - if not - 3. 54's work quite well. Hope this helps.



Bob

 

[dpuckett]

RHancock,



From what I've read here, and a few other people I've talked to, I'd venture to guess you are at your max safe rpm now, at least for sustained periods under load. The only thing I can think of would be a swap to 3. 54s or go with an aftermarket overdrive, such as Gear Vendors or US Gear. These units are in the 20-22% OD range, if I'm not mistaken. Last I heard, they are about $2200 for the gearbox, then installation. The 20% will give you about the same as a 3. 28 rear ratio; final ratio of 2. 52 or so. Sorry, dont have calculator handy, doing it on paper. So you have to ask yourself, how much is it worth to go faster? If you lower your rpms 20%, you should see a similar gain in mpg, esp if you run against the governor; all else being equal. If you put a lot of miles on your truck in a year (such as the 30-40K I do) it may well be worth it. To me, it isnt worth it, I just get there a little later. Still get 20 mpg or so at 65.

Daniel

 

[RHancock]

I thought about changing gears, don't know yet, I will run a taller tire when these Michelin's finally wear out and see how that works. I really like the 4. 10's for towing, going up grades at 70 with a trailer is really nice. Just here on the beltway you have to run 70+ or you will get run over...

 

[soslow91]

3. 54's would give you the ability to go almost 16% faster and you would normally get better mileage but if you just drive 16% faster I have my doubts you'll see much improvement. One thing you should consider is whether its through taller gears or a gear vendor or taller tires anything that decreases rpm at a given speed increases the load on your transmission.



I'm pretty sure the motor can handle going a little faster but the injection pump may not like it in stock form I think you can upgrade the pump for more reliability at higher rpm you'll have to do a search on that one unless you can afford to have piers do it Nascar Mark runs about 3600 on the dyno I think so maybe you could ask him.