Tuning Twins

[Extended Power]

I tried using the final boost pressure, but could not keep lines on. (Too loose, and they pop off...too tight, and the clamp cut into the hose, and blew off anyways....tried tie wraps...they worked ok.)
And tring to use the primaries outlet pressure takes too long to build up enough to actuate the waste gate.
I switched over to the spring style waste gate actuator...easier to set, way less room taken up...no ugly hoses or lines.

 

[jgsturbo]

How can I spin the secondary harder if i already have the wastegate completely shut?


Sent from my ADR6400L using Tapatalk

Saw this and had to add that even if you pinch off the WG control lines, the poppet valve will still open when the DP over comes the spring inside the gate.
Put full BP to the port that closes the WG valve (nothing in the WG open port) if you want to hold most gates shut.

:Cheer:

 

[stlcummins]

Mine is taken boost from the primary to the actuator on the secondary. However, my twins are a small set and spools like lightning.....

one question i have been thinking about here lately is where is the best place to take pressure from to control the secondary waste gate? exhaust manifold? i have heard of people using spring setups and getting the secondary to the desired boost without the primary to secondary boost pipe connected...i just haven't really heard this talked about.

 

[jgsturbo]

Continuing on this thread I believe I have an idea to add....
Its mentioned here in this thread that in the lower rpms letting the HP turbo build most of the pressure makes for better bottom end. And letting the LP build more of the PR makes better topend.
So what I'm reading is we need a boost controller that lets the HP charger build most of the PR till mid rpm (or at least til the LP charger has enough DP flow to take over) then switches to a lower HP charger boost setting after that RPM to maximize the topend airflow which seems to be letting the larger LP charger do more PSI %.

Basically a RPM switch, 3 way solenoid and a couple of regulators would be the simple version but it would accomplish the best of both.

Summit Racing SUM-830449-1 - Summit Racing RPM-Activated Switches - Overview - SummitRacing.com

Stacking Solenoid Valves | MSCDirect.com
Regulators - Regulators | MSCDirect.com

Hmmm.

 

[stlcummins]

I get it, kinda like shifting a Lenco with nitrous bottle pressure. Nice.But it might not work good for guys that tow since rpm switches can't designate engine load... jmo.

Continuing on this thread I believe I have an idea to add....
Its mentioned here in this thread that in the lower rpms letting the HP turbo build most of the pressure makes for better bottom end. And letting the LP build more of the PR makes better topend.
So what I'm reading is we need a boost controller that lets the HP charger build most of the PR till mid rpm (or at least til the LP charger has enough DP flow to take over) then switches to a lower HP charger boost setting after that RPM to maximize the topend airflow which seems to be letting the larger LP charger do more PSI %.

Basically a RPM switch, 3 way solenoid and a couple of regulators would be the simple version but it would accomplish the best of both.

Summit Racing SUM-830449-1 - Summit Racing RPM-Activated Switches - Overview - SummitRacing.com

Stacking Solenoid Valves | MSCDirect.com
Regulators - Regulators | MSCDirect.com

Hmmm.

 

[jgsturbo]

But if your already at an RPM high enough to light the large charger, spool will be instant.
Also its just a change in WG settings, not a HUGE change.

 

[stlcummins]

Gotcha.

 

[$and$hark]

Very Informative. Subscribing.

 

[me2]

Originally Posted by rdix7991
Well if you have 65 total and 28 is coming from the primary then the secondary must be making 65-28 = 37. Right?
No, not even close.

I'm trying to understand this.

The intake manifold pressure is 65 PSI. The interstage pressure is 28 PSI. The pressure differential across the secondary compressor IS 65-28 PSI = 37 PSI.

I think that is correct.

I think the reply to the question is misleading.

What isn't correct is to assume that the compressors are working the same amount as their pressures indicate, ie the lower compressor is working 28 PSI and the upper is working 37PSI, so the secondary is working harder.

What is correct is that the first compressor is compressing about 14PSI air to (14.7 + 28 PSI), so it is operating at a PR of 3.05.

The second compressor is compressing (28 + 14.7) to (65 + 14.7), so it is operating at a PR of 1.86.

So the primary compressor is working much harder than the secondary, PR of 3.05 versus 1.86, even though the primary is producing a boost of 28 PSI and the secondary has a boost of 37 PSI.

Do I have this all correct ?

 

[AHall]

Read through the compound turbo threads. Remember its never +- psi.

 

[me2]

Read through the compound turbo threads. Remember its never +- psi.

?????

If the manifold is at 65 PSI and the interstage is at 28 PSI, ignoring temperature effects, the second turbo has 37 PSI across it. There is no math that I know of that negates that. If there is, please explain otherwise.

 

[White Knight]

You're right, there is a 37psi differential. But really pressure measurements should not be used in turbo discussions. Pressure ratio is what matters and that's what should be discussed. Pressure is largely irrelevant once you know the pressure ratio.

 

[me2]

You're right, there is a 37psi differential. But really pressure measurements should not be used in turbo discussions. Pressure ratio is what matters and that's what should be discussed. Pressure is largely irrelevant once you know the pressure ratio.

I totally agree. Thus my previous post.

 

[Big Blue24]

I'm trying to understand this.

The intake manifold pressure is 65 PSI. The interstage pressure is 28 PSI. The pressure differential across the secondary compressor IS 65-28 PSI = 37 PSI.

I think that is correct.

I think the reply to the question is misleading.

What isn't correct is to assume that the compressors are working the same amount as their pressures indicate, ie the lower compressor is working 28 PSI and the upper is working 37PSI, so the secondary is working harder.

What is correct is that the first compressor is compressing about 14PSI air to (14.7 + 28 PSI), so it is operating at a PR of 3.05.

The second compressor is compressing (28 + 14.7) to (65 + 14.7), so it is operating at a PR of 1.86.

So the primary compressor is working much harder than the secondary, PR of 3.05 versus 1.86, even though the primary is producing a boost of 28 PSI and the secondary has a boost of 37 PSI.

Do I have this all correct ?

You are correct.

 

[jsf350]

ok every time i think i get it i get lost again.....
twins are a 66 over a 84

total boost is 80 psi

pressure out of the 84mm is about 27 psi

how is my pressure ratio looking? and i dont understand the math to figure it out

thanks

 

[5.9 Cummins Fan]

I believe your primary is at 2.83 PR and your secondary is at 2.962. Looks pretty good Joel

 

[me2]

You are correct.

Thanks. BTW, I love your truck, specifically how you set up an awesome, low cost turbo system on it and the performance you get from it. I also love the way it cleans up once the turbos spool. Well done !

 

[me2]

ok every time i think i get it i get lost again.....
twins are a 66 over a 84

total boost is 80 psi

pressure out of the 84mm is about 27 psi

how is my pressure ratio looking? and i dont understand the math to figure it out

thanks

80 -27 = 53.

PR of the 84 is
(27 + 14.7) / 14.5 = 2.875.

PR of the 66 is
(53+ 14.7) / (27+14.7) = 1.62.

Just remember to use absolute pressures for everything.

I assumed the absolute pressure at the intake of the 84 was 14.5 PSI absolute. If you live at altitude and/or you have a dirty air filter, the PR will be even higher.

 

[me2]

OK I have came up with the pressure ratios and such for the elevation where I live. Here is what I came up with

Amospheric pressure at 4500 ft=12.46 psi

PR primary=(Boost PSI+12.46) / 12.46

PR secondary=(Boost PSI of secondary+12.46) / (Boost PSI of primary+12.46)

Umm... I don't mean to be a nit picker, but those equations are actually wrong. Not sure if they were corrected later in the thread as I didn't read it all closely, so I thought I'd speak up.

The equation for absolute pressure is gauge pressure + 14.7 PSI.

With that correction, the equations should be

PR primary=(Boost PSI + 14.7) / 12.46
PR secondary=(Boost PSI of secondary+14.7) / (Boost PSI of primary+14.7)
where boost PSI of the secondary = manifold pressure - primary pressure.

 

[5.9 Cummins Fan]

Umm... I don't mean to be a nit picker, but those equations are actually wrong. Not sure if they were corrected later in the thread as I didn't read it all closely, so I thought I'd speak up.

The equation for absolute pressure is gauge pressure + 14.7 PSI.

With that correction, the equations should be

PR primary=(Boost PSI + 14.7) / 12.46PR secondary=(Boost PSI of secondary+14.7) / (Boost PSI of primary+14.7)
where boost PSI of the secondary = manifold pressure - primary pressure.

12.46 is the atmoshperic pressure at my elevation. The secondary compounds the primary. If total is 80 and the primary is making 27 the secondary is compounding it at the ratio of 2.962 if we are at sea level.

27(x)=80

x=80/27

x=2.962 PR of secondary so the secondary is actually making 28.8414 psi


(27+14.7)/14.7=2.83 PR primary

So Joel's setup is right around 1.0466:1.0 not bad at all

And I do agree that it is gauge pressure plus amosperic pressure, thats why I add the atmosperic to the gauge reading in the equation. Oh and the secondary PR or pressure is what I think you are getting at is not the total manifold pressure minus the primary pressure. The secondary is compounding the air being moved by the primary. Not trying to be a dick