Tuning Twins

me2 said:
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.
Click to expand...

Also you posted the exact same equations, didn't change anything except forgot to change the 12.46 atmospheric pressure out with 14.7 sea level atmospheric pressure. Not to be a nit picker.
 
5.9 Cummins Fan said:
Also you posted the exact same equations, didn't change anything except forgot to change the 12.46 atmospheric pressure out with 14.7 sea level atmospheric pressure. Not to be a nit picker.
Click to expand...

The use of 12.46 PSIA for the absolute pressure at the inlet of the turbocharger was correct in that case.

We could take this to another level and argue about what the gauge we are reading the pressures from is calibrated to, but I'm not going there. The working convention is to use PSIA = PSIG + 14.7 for all turbo pressures.

See here, for example.
Turbocharger Compressor Calculations
 
me2 said:
The use of 12.46 PSIA for the absolute pressure at the inlet of the turbocharger was correct in that case.

We could take this to another level and argue about what the gauge we are reading the pressures from is calibrated to, but I'm not going there. The working convention is to use PSIA = PSIG + 14.7 for all turbo pressures.

See here, for example.
Turbocharger Compressor Calculations
Click to expand...

Thank you for agreeing with me. I started this thread to gain insight and help others, not for someone to swoop in and claim it is all wrong. I do realize that changing the atmosperic pressure for a certain elevation is going to make a miniscule difference in the overall outcome on a turbocharged application but I am a perfectionist so I chose to use the precise pressure at my elevation. Here is a quote from your link.... "Absolute pressure is the gauge pressure (measured by a gauge that reads 0 when it is open to the outside air) plus atmospheric pressure. Atmospheric pressure is about 14.7 psi at sea level."
Air is denser at sea level than at higher altitudes. If you want to get all crazy you can get into humidity and pretty much every other atmosperic condition.

Do some more reading and real world testing before you try to sound like a been there done that kinda guy. If you really knew that much about compounds you wouldn't be asking for advice on a he351/a7500 setup.
 
5.9 Cummins Fan said:
If you really knew that much about compounds you wouldn't be asking for advice on a he351/a7500 setup.
Click to expand...


thankyou2.gif
Hands on experience means.... Oh so much..
 
thanks guys
the pr of the 84mm i was able to get.... i had issues with figuring the 66

everything has now changed with the new motor build and ive also upgraded the 84mm to a 91mm
 
5.9 Cummins Fan said:
Thank you for agreeing with me. I started this thread to gain insight and help others, not for someone to swoop in and claim it is all wrong. I do realize that changing the atmosperic pressure for a certain elevation is going to make a miniscule difference in the overall outcome on a turbocharged application but I am a perfectionist so I chose to use the precise pressure at my elevation. Here is a quote from your link.... "Absolute pressure is the gauge pressure (measured by a gauge that reads 0 when it is open to the outside air) plus atmospheric pressure. Atmospheric pressure is about 14.7 psi at sea level."
Click to expand...

Before you start doing that, you should account for the ACTUAL air inlet pressure on the first turbo. Because unless you are running a turbo open to the atmosphere, you are going to have pressure loss (that varies with flow, btw) from the inlet piping and the air filter. If you've ever looked at a filter minder in the real world, you would have known this.

And if you are running a turbo open to atmosphere, the pressure at the inlet isn't going to be atmosphere when you are running down the track at 75 MPH.

A half PSI pressure difference at the inlet of a turbo running at a PR of 3 or 4 makes a sizeable change to the outlet pressure.
 
Using "dvst8r" formula from post #100, I made up a Spread Sheet on "MS Excel" to record data and easily see the pressure ratios between chargers.. I use a mounted video camera to record three gauges (Drive Pressure, Primary Charger and Overall Boost) at once while driving..

PM me your email address and I will be glad to send it to you..

I have updated the first spread sheet I posted awhile back.. I found some errors on it..
 
Waste gate opens by drive pressure

Adjusting the OE waste gate (Actuator Spring Tension Only) to crack @ 38-40lbs. and allowing drive pressure to open the waste gate has resulted in the best performance, Lowest EGT's and best ratios between chargers I have seen yet..

Using the OEM Actuator without any pressure connections from the charger I believe, keeps the Waste Gate closed longer until the DP over comes the spring tension.. It has by far produced the best Ratio's between the Chargers. I can't believe how low the EGT's stay @ 50-60lbs. of boost..

In the "You Tube" Video, The Gauges from top to bottom are: Overall total boost, Primary Turbo Boost, Bully Dog "Watch Dog" (RPM's, EGT's, Eng. Coolant Temp & Eng. Load), Bottom left is Drive Pressure...

http://youtu.be/qh-dE-HQj0w
 
Okay, I'm playing with my new setup which is a 57/65/14 s300 over a 75/83-74/1.10 s400. Right now I'm seeing 75 psi overall with 30 psi on the primary.

So (30+14.7)/14.7 = 3.04 primary
(75+14.7)/(30+14.7) = 2 secondary

Is this within the map range of the secondary? Im running a stainless diesel spring gate and I've tightened it almost all the way to get the pr's to where they are now. I'm going to try to get a dp gauge in this weekend to see what's happening in that area.


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chevota84 said:
Okay, I'm playing with my new setup which is a 57/65/14 s300 over a 75/83-74/1.10 s400. Right now I'm seeing 75 psi overall with 30 psi on the primary.

So (30+14.7)/14.7 = 3.04 primary
(75+14.7)/(30+14.7) = 2 secondary

Is this within the map range of the secondary? Im running a stainless diesel spring gate and I've tightened it almost all the way to get the pr's to where they are now. I'm going to try to get a dp gauge in this weekend to see what's happening in that area.


Sent from my DROID X2 using Tapatalk 2
Click to expand...

At 75lbs. of total boost the primary is doing 76% of the work and your secondary is @ 15lbs doing 33% of the work..

I have a spread sheet that calculates the ratios between chargers, you can put in your boost numbers from lowest to highest and you can see what is going on between the chargers and you can also set your WG by seeing the ratio's as boost is building.. PM me with your e-mail..
 
rlawless said:
At 75lbs. of total boost the primary is doing 76% of the work and your secondary is @ 15lbs doing 33% of the work..

I have a spread sheet that calculates the ratios between chargers, you can put in your boost numbers from lowest to highest and you can see what is going on between the chargers and you can also set your WG by seeing the ratio's as boost is building.. PM me with your e-mail..
Click to expand...

Send me the spreadsheet to if you don't mind
Aross@ross-sons.com



Sent from my Galaxy Nexus using Tapatalk 2
 
rlawless said:
At 75lbs. of total boost the primary is doing 76% of the work and your secondary is @ 15lbs doing 33% of the work..

I have a spread sheet that calculates the ratios between chargers, you can put in your boost numbers from lowest to highest and you can see what is going on between the chargers and you can also set your WG by seeing the ratio's as boost is building.. PM me with your e-mail..
Click to expand...

If I could get that also I would appreciate it.
tjasonsmith@ymail.com

tapatalking from droidx
 
rlawless said:
At 75lbs. of total boost the primary is doing 76% of the work and your secondary is @ 15lbs doing 33% of the work.. .
Click to expand...

With a little reverse math it looks like I'd be in the 100 psi neighborhood to get my secondary PR in the 2.5 range. I'm not sure if the 24v is going to be real happy about that lol


Sent from my DROID X2 using Tapatalk 2
 
rlawless said:
At 75lbs. of total boost the primary is doing 76% of the work and your secondary is @ 15lbs doing 33% of the work..

I have a spread sheet that calculates the ratios between chargers, you can put in your boost numbers from lowest to highest and you can see what is going on between the chargers and you can also set your WG by seeing the ratio's as boost is building.. PM me with your e-mail..
Click to expand...

I'd also like a copy of that spreadsheet to compare some of my rough guesstimations please. saucoin@hotmail.com
 
I have a spread sheet that calculates the ratios between chargers, you can put in your boost numbers from lowest to highest and you can see what is going on between the chargers and you can also set your WG by seeing the ratio's as boost is building.. PM me with your e-mail..[/QUOTE]

This seems helpful, I would appreciate one as well. aeilert@ksu.edu
 
rlawless said:
At 75lbs. of total boost the primary is doing 76% of the work and your secondary is @ 15lbs doing 33% of the work..

I have a spread sheet that calculates the ratios between chargers, you can put in your boost numbers from lowest to highest and you can see what is going on between the chargers and you can also set your WG by seeing the ratio's as boost is building.. PM me with your e-mail..
Click to expand...

I'm seeing 64psi total boost and 24psi out of my primary. I'm running a Hx40 over HT3B.
 
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