Ideal pressure to feed modded CP3? Dual feed line proof?

[JStieger]

Is there an ideal fuel pressure to feed the modded CP3? Is there a point where CP3 inlet pressure is too high?



Looking for answers from folks that have run consecutive dyno runs or perhaps 1/4 mile runs while just adjusting the modded CP3 inlet pressure between runs.



While we're at it, is there any documented proof that the dual feed line works, i. e. before and after dyno runs on the same day. I've read that some (e. g. , JPLipert on here) have gained one more TST level, while others have gained nothing. I remember reading on DTR that maybe OT-OF-HERE was going to dyno before and after???

 

[JLibert]

Julius,



As you just stated, I was able to gain 1 level on the tst with the addition of the dual feel line. I also noticed the there wasn't a dip in power like before.



As far as the inlet pressure to the cp3..... Well as you may remember from the post (fass 95 enough?) everybody with the exception of maybe 1 person said that 10 psi with the fass 95 wasn't enough for my mods, and that it was costing me power vs. what a pump set up for approximately 40psi would give me. Well, I pulled off the fass 95, and my 30psi dipricol gauge, installed the walbro 392, shimmed to 42 psi, and... ... ... ... ... ... ..... no difference as far as I can tell. The pump is very quiet, very easy to tune etc, but power wise I don't feel it at all. Sorry, no dyno runs or 1/4 mile runs--- but I do drive my truck a lot (115k on an 04. 5) and I drive the same roads every day, so with some certainty I can say that I didn't notice a difference in 40 psi vs 15psi. It might have made my cp3 a little noiser, maybe?

 

[JStieger]

Thanks for the reply!



I just shimmed my pressures up to ~37 psi from 30 psi this afternoon. The thing is as the pressure comes up, the fuel volume drops so in my mind I see a dilemna:



1) in order to get volume to the CP3 we need to pump at less pressure, but...

2) by having a higher pressure to the CP3, we take better advantage of the pressure multiplication in the CP3. At the same time I don't want to run at too high pressure because then the pump is just working harder - possibly needlessly.



I wonder what the crossover point is for optimum volume and pressure without working the pump too hard or recirculating fuel around excessively?



I'm going to try to dyno again in a few weeks in Boise - I wonder if anyone has a dual feed line to loan me to test back to back? :-laf

 

[AK RAM]

Knowing your pump, you would probably have to ask if it will help. For everyone else, the difference should be dependant on which Cp3 you run as the two front-runners are made differently inside. One company performs a slew of low pressure pump and FCA mods in addition to plunger upgrades (Pump A) and one company performs just the plunger upgrades (Pump B). Pump A with the low pressure pump and FCA mods will benefit from higher lift pump pressure, but you have to really get pressure up there. Pump B, without the low pressure pump and FCA mods, does not respond to higher feed pressures.



I have only seen one dyno documented increase like you referred to and it came from hitting Pump A with 120psi with a single Walbro (dead-headed just to see what happened) verses the 25-or-so-psi it got fed on a daily basis. Gains were either 60 or 80hp (I forget which one…. its been a while). Hitting the Cp3 with 120psi didn’t make the increase; it just enabled the other mods to make the increase, hence individual results will vary. That thread is on one of the boards somewhere (I believe DTR).

 

[JLibert]

Thanks for the reply!



I just shimmed my pressures up to ~37 psi from 30 psi this afternoon. The thing is as the pressure comes up, the fuel volume drops so in my mind I see a dilemna:



1) in order to get volume to the CP3 we need to pump at less pressure, but...

2) by having a higher pressure to the CP3, we take better advantage of the pressure multiplication in the CP3. At the same time I don't want to run at too high pressure because then the pump is just working harder - possibly needlessly.



I wonder what the crossover point is for optimum volume and pressure without working the pump too hard or recirculating fuel around excessively?



I'm going to try to dyno again in a few weeks in Boise - I wonder if anyone has a dual feed line to loan me to test back to back? :-laf

Julius,



did you notice any increased noise when raising the inlet pressure? I'll guess that you didn't notice any increase in power, did you?

 

[JStieger]

did you notice any increased noise when raising the inlet pressure? I'll guess that you didn't notice any increase in power, did you?

No extra noise at all. I did notice that my throttle is a bit more touchier now. And it looks like the rail pressure comes on a bit quicker off idle just by watching the gauge as I take off.



This is what's weird... prior to this change I had the Smarty Wild aftermarket injector program on and it was way too touchy for me. The Moderate aftermarket program was too doggy like stock. So for grins-and-giggles I loaded up the stock injector Moderate program and it felt in between - just perfect.



Then I upped the CP3 inlet pressure and now the scales have tipped more to the Wild program feel. More throtttle sensitivity, but not as jerky as the Wild. That's the only way that I can describe it.

Knowing your pump, you would probably have to ask if it will help

I will ask...

 

[AK RAM]

Here is a post on CF by RC Cox where he picked up 30hp hitting his pump with 120psi via a RASP. He doesn't have any mods to the low pressure pump where the extra feed pressure comes into play, so that is a suprise to see... ... just some FCA tweaks on his Relentless hyperdrive gear'd stock Cp3: http://www.cumminsforum.com/forum/3...nsiderations-dual-vs-single-4.html#post183580