363 over s475

[Jonny]

Hey guys I got a few questions I just installed a compound turbo kit on my 2000 Cummins. My question is why does the small charger need to be set at 25 psi? The lowest I could get it with the Boost elbow is 32 psi when it starts to open, I don't think I can adjust the actuator because it does not have a nut on it. What would the harm be if I just left it at 32 psi? Thanks everybody

[Mopar1973Man]

@jlbayes would be a good one to ask.

 

Another is @TFaoro he should know as well.

[jlbayes]

It doesn't need to be set at 25psi. Do you have an interstage boost gauge and a drive pressure gauge? The boost going to the secondaries waste gate is for reference only.

[Jonny]

Thank you jlbayes i love when you comment on my stuff lol...so im fine just leaving the 63/68 at the 32?and no i dont have a interstage boost gauge but its on its way

[trreed]

The wastegate is going to control how hard each turbo works.  It also sees total pressure.  So the earlier it opens, the more work the primary will do. ~32 is where mine seems to be happiest.  Good rule of thumb one you get the interstage boost gauge in is to get each turbo to be doing half the work.  

[Jonny]

Si if my secondary is say 30 going down the road,i want my primary at approx 15?

[trreed]

Total boost would be 30. But yes, 50/50.  And it'll be as close as you can get it. For me, light throttle cruising I'm at 5 from the primary and 10 total.  Moderate acceleration my secondary makes a few more psi than the primary.  and WOT the two are split perfectly 50/50.

[jlbayes]

Which is the reason for the other gauges. Need to do some maths to get them close. I prefer the primary to do more work but it makes the setup more laggy.

[Jonny]

So what do i do if my secondary is 30psi and the primary is say 25? What is the plan of action to get it to a one-to-one? Sorry so many questions I'm just trying to learn and I really appreciate you explaining stuff

[trreed]

http://atptrucks.com/blog/compound-turbos-and-boost-numbers-the-math/

I found this as I was trying to refresh my own memory just now.  Pretty helpful and a better explanation than what I gave.

Edited March 5, 2018 by trreed

[jlbayes]

(atmospheric pressure) + (overall boost) divided by (atmospheric pressure) = overall P/R
(atmospheric pressure) + (primary boost) divided by (atmospheric pressure) = primary P/R
(Overall P/R) divided by (Primary P/R) = Secondary P/R
(Secondary P/R x (atmospheric pressure) minus (atmospheric pressure) = Secondary Boost

12+60/12=6

12+30/12=3.5

6/3.5=1.71428

1.71428*12-12=8.57136

 

 

These are Trevors numbers. Secondary pr is low. Be nicer to see it closer to 2.

 

[Jonny]

Thank you guys i really appreciate it.i will post numbers once my interstage gauge shows up

[Jonny]

So i got the bung and gauge done for the interstage boost..can i do the numbers for where the truck will spend its time towing?if so total boost is 30 and primary is at 13-14psi...or does it need to be full throttle run?

So heres the math at utah 14psi ( atmo)

30+14÷14=3.14 (overall)

14+14÷14=2 (primary)

3.14÷2=1.57 ( secondary pr)

1.57×14-14=7.98 (secondary boost)

 

Edited March 13, 2018 by Jonny
Did math wrong ha ha

[jlbayes]

I do my math based on wot as it is typically a constant. Your numbers look ok for part throttle operation. I would tighten the gate to try and get the secondary pr to come up as it will help with response.

[Jonny]

Awesome thank you for the reply...so will the secondary usually always work harder until the gate opens to dump to the primary?

[jlbayes]

Yes as it spools first. The primary is what cools everything off once it is up and moving.