Rail Pressure

[1911 guy]

Hi was just wondering what the max safe limit is for rail pressure ? At what point does the relief valve pop? Can i run for extended periods of time on the highway while towing and not risk damaging anything. By the way i am running the TST R49. Ive noticed that throttle response is greatly increased with elevated levels of RP.

 

[OT-OF-Here]

Everything I've read says,..

Hi was just wondering what the max safe limit is for rail pressure ? At what point does the relief valve pop? Can i run for extended periods of time on the highway while towing and not risk damaging anything. By the way i am running the TST R49. Ive noticed that throttle response is greatly increased with elevated levels of RP.

that 29k is RV suicide and basically Red Line. You need to have and maintain over/in excess of 23.5k when making power. With that being said, I think the 26k/27k psi at wot would be a great tarket number.

 

[triton]

it's strange that the rail pressure it seems everyone runs is higher than the RV will blow at.

I had a long conversation with a very knowledgeable Cummins tech recently. This last year he spend half at school ( continued ed ) and half at work. He said that per D/C, the RV is set to blow at 23K... period, some aren't perfect so they may handle a little more.

So, either his schooling is wrong or, there's a lot of people running around with bad RV's. I've seen 26K myself but, haven't noticed poor starting or any other symptom that would make me think it's bad.

 

[Billyram]

My truck is 4 yrs old and still has the original r/v. I ran the drb and the ecm would call for 26.7K before smarty. So I would think the r/v would be set a bit higher than what the ecm would call for. I see 24.5K at wot and when I let off I get a spike arround 27.5K so I would think the r/v may be set for 27.5-28K. I believe the cr trucks need to operate arround 20-24K to make power.

 

[1911 guy]

23 and 24K seems a bit weak since i can easily get it up to 24K Only on level 7 while in the econ mode. So what happens when RV limit is exceeded? and how does the engine act after? So is there any chance of pump or injector damage running this thing at elevated pressures over long periods?

 

[Billyram]

Some pressure boxes can run the pressure above the limits of the r/v and don't back down at crusing speed. Constant over pressure will damage the r/v where it want hold pressure. The injectors on the 03 can't stand much of this and 04.5 injectors can go too.

 

[GUNNAR]

At that kinda a Pressure you should be hearing a "rattle". Single pump trucks just plug it. If you have larger injectors than the relief valve will hold higher pressure for a longer time than the factory "Preset" due to increased flow. If you aren't doing anything with the pressure you are making then failure is going to happen much sooner in it's life span. $.02

 

[triton]

23 and 24K seems a bit weak since i can easily get it up to 24K Only on level 7 while in the econ mode. So what happens when RV limit is exceeded? and how does the engine act after? So is there any chance of pump or injector damage running this thing at elevated pressures over long periods?

I'm no expert on the issue but...

the better the rail pressure the better the atomization of the fuel. There are limits though. On a stock set up, 23/24K RP is actually a little high from what I've seen in my truck. Running psi is between 15 and 20psi. At WOT you'll see 23/24K. With some sort of performance box you'll see higher RP's but, 26 to 27K should be the max.

When the limit of the RV is exceeded and it blows, your truck will have very hard starting, if it starts at all. Cummins sell a bolt that can be used to test the RV or one can be made.

People do cap the RV but, IMO... Bosch put it there for a reason. That's a lot of psi to blow if there were a problem and the RV is there to help prevent it.

I don't think you'll see much damage from RP, unless it gets too high. The pump is making that pressure and from what I understand is capable of over 30Kpsi. Too much psi and you could crack and injector though.