Tuning Twins

dvst8r said:
No, not even close.
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:doh: Well I gave it my best shot.

This thread is helping me understand this a WHOLE lot better. I see why I was wrong now. The Primary charger is being compounded by the Secondary, so the boost pressure would change upon going though. I guess that is why you need to calcualte the PR's to find out how hard each turbo is working.

Keep the info coming! :pop:
 
dvst8r said:
You are essentially at sea level so we will use 14.7psi as atmospheric pressure.

To figure out how much work each charger is doing, you need to convert to pressure ratio's first. So the formula is (atmospheric pressure + gauge pressure) / atmospheric pressure

65psi gauge overall boost is = (14.7+65psi)/14.7 = ~5.42
28psi gauge primary boost is = (14.7+28psi)/14.7 = ~2.91

So we now divide overall PR by primary PR, and then convert back
5.42 / 2.91 = 1.86

Secondary PR = ~1.86PR So using the above formula just in reverse
1.86 * 14.7 - 14.7 = 12.68psi so call it 13psi.

So currently your primary charger is doing more work then your secondary. This could happen do to a number of things, as was suggested the two things to try if you are worried about it, would be:

-Take out those silly brass pop off valves, all they do is cause boost leaks that over speed chargers.

-Mechanically tie the gate closed on the secondary, to make sure drive pressure isn't blowing it open.
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Thanks.will do both.

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Now, compare your numbers to the peak numbers I see on the Junker Drag Truck with He351cw(60mm) over HT4B(83mm).

At the very end off a 1/4 mile pass up in the 3500 rpm range in overdrive, I see 85 psi total and 54 psi between stages.

Atmospheric conditions in Las Vegas usually hover right around 14.5 psi.


(85 psi + 14.5 psi) / 14.5 psi = 6.86 overall PR

HT4B (54 psi + 14.5 psi)/ 14.5 psi = 4.72 PR

6.86/4.72 = 1.45 PR for He351 secondary turbo

1.45 * 14.5 - 14.5 = 6.57 or about 7 psi if run at atmospheric conditions.


Yep, that stock ported internal wastegate seems to be doing just fine at controlling the second stage turbo speed.
 
Big Blue24 said:
Now, compare your numbers to the peak numbers I see on the Junker Drag Truck with He351cw(60mm) over HT4B(83mm).

At the very end off a 1/4 mile pass up in the 3500 rpm range in overdrive, I see 85 psi total and 54 psi between stages.

Atmospheric conditions in Las Vegas usually hover right around 14.5 psi.


(85 psi + 14.5 psi) / 14.5 psi = 6.86 overall PR

HT4B (54 psi + 14.5 psi)/ 14.5 psi = 4.72 PR

6.86/4.72 = 1.45 PR for He351 secondary turbo

1.45 * 14.5 - 14.5 = 6.57 or about 7 psi if run at atmospheric conditions.


Yep, that stock ported internal wastegate seems to be doing just fine at controlling the second stage turbo speed.
Click to expand...

That is sweet!^ How much did you port it?
 
Big Blue24 said:
Now, compare your numbers to the peak numbers I see on the Junker Drag Truck with He351cw(60mm) over HT4B(83mm).

At the very end off a 1/4 mile pass up in the 3500 rpm range in overdrive, I see 85 psi total and 54 psi between stages.

Atmospheric conditions in Las Vegas usually hover right around 14.5 psi.


(85 psi + 14.5 psi) / 14.5 psi = 6.86 overall PR

HT4B (54 psi + 14.5 psi)/ 14.5 psi = 4.72 PR

6.86/4.72 = 1.45 PR for He351 secondary turbo

1.45 * 14.5 - 14.5 = 6.57 or about 7 psi if run at atmospheric conditions.


Yep, that stock ported internal wastegate seems to be doing just fine at controlling the second stage turbo speed.
Click to expand...

Why does everyone say to set pressure ratios the same?

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inline6power said:
Why does everyone say to set pressure ratios the same?

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Who said that? Set them where the chargers are working within their map. I would plug the pop off ports and adjust the wastegate.

Your gettin close Adam, keep at it.
 
This is some good info. I am still trying to tune my chargers in and am confused on if my numbers work. I still dont understand how they should match because looking at your guys numbers and mine it seems way off. Take a look and see what you think.

1000ft elevation

(14.17+50)/14.17=4.52 Overall
(14.17+26)/14.17=2.83 Primary Garrett TV8403 Comp 88/116 Turbine 111/101 1.39 AR
4.52/2.83=1.59 Secondary Garrett GT4294
1.59*14.17-14.17=8.36 psi
 
shiftycapone said:
Who said that? Set them where the chargers are working within their map. I would plug the pop off ports and adjust the wastegate.

Your gettin close Adam, keep at it.
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I have been told you want them sharing the work equally. No way to do that unless pressure ratios were the same

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For the compressor side, it would be best if both turbos were operating in their peak efficiency in the compressor map. The PR that this happens at is not the same for a large turbo as it is for a small one. Having said that, large turbos may move more air more efficently, then a small turbo, even though it is in a less efficient place on it's map.

Another problem is so far only the compress side has been discussed. The turbine side needs to be considered as well.

Paul
 
paulb said:
For the compressor side, it would be best if both turbos were operating in their peak efficiency in the compressor map. The PR that this happens at is not the same for a large turbo as it is for a small one. Having said that, large turbos may move more air more efficently, then a small turbo, even though it is in a less efficient place on it's map.

Another problem is so far only the compress side has been discussed. The turbine side needs to be considered as well.

Paul
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Makes much more sense to get them both in thief map rather than sharing work equally. That being said my secondary map is around 30. Three plus 28 from the primary would be crazy boost. How would you get both in their efficient range yet keep boost controllable

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inline6power said:
Makes much more sense to get them both in thief map rather than sharing work equally. That being said my secondary map is around 30. Three plus 28 from the primary would be crazy boost. How would you get both in their efficient range yet keep boost controllable

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I'm guessing that the 30 you are talking about is at the top of the peak efficiency map. Depending on the S475, the top is usually at 2.5PR and the bottom of the peak efficiency map is about 1.7PR. Go more to the bottom, but stay away from the surge line.

Paul
 
paulb said:
I'm guessing that the 30 you are talking about is at the top of the peak efficiency map. Depending on the S475, the top is usually at 2.5PR and the bottom of the peak efficiency map is about 1.7PR. Go more to the bottom, but stay away from the surge line.

Paul
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Perfect thanks Paul

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RIGHTEYEBLIND said:
This is some good info. I am still trying to tune my chargers in and am confused on if my numbers work. I still dont understand how they should match because looking at your guys numbers and mine it seems way off. Take a look and see what you think.

1000ft elevation

(14.17+50)/14.17=4.52 Overall
(14.17+26)/14.17=2.83 Primary Garrett TV8403 Comp 88/116 Turbine 111/101 1.39 AR
4.52/2.83=1.59 Secondary Garrett GT4294
1.59*14.17-14.17=8.36 psi
Click to expand...

Where did you come up with 14.17? I just checked the current weather in Fairbanks, AK and the barometer is 29.53" that equates to 14.504 psi. It looks like you have a low pressure storm system blowing through so that is probably a little lower than your typical pressure.

Also, looking at your numbers, your twin setup only makes 50psi max boost on the boost gauge? 71mm over 88mm twins? Sounds like you have a bad boost leak or no fuel.
 
inline6power said:
I have been told you want them sharing the work equally. No way to do that unless pressure ratios were the same

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Click to expand...


If you share the work between the turbos, in theory, it should heat the air less than running one at a super high pressure ratio where it is marginally efficient (adding lots of extra heat to the air charge), and then letting the second one putt along.


In real life, sharing the load isn't necessarily the most efficient setup. For example, with my turbos being so much different in size 60mm and 83mm, if I tuned the wastegate to where they shared the load, I would have so much extra back pressure that I'm sure it would make less horsepower. Just think about it, if I take the full charge of 120 lbs/min of air mass from the HT4B and try to double it's pressure with a 60mm He351 turbo that normally handles 65 lbs/min of air mass, it's going to take more "shaft horsepower" to reach the "balanced" 3.4 PR than it would if it was handling it's normal 65 lbs/min. Shaft horsepower comes from the turbine wheel. The turbine wheel on the He351 is so small, it would probably take 140 psi drive pressure to create enough shaft horsepower to compress 120 lbs/min of air.

I don't think there is a way to calculate the "ideal" real-world pressure ratio for a twin setup on our trucks that have so many variables and unknown values. The only way to pinpoint peak horsepower is to test and tune on a dyno or make passes down the dragstrip at different wastegate settings.
 
Big Blue24 said:
Now, compare your numbers to the peak numbers I see on the Junker Drag Truck with He351cw(60mm) over HT4B(83mm).

At the very end off a 1/4 mile pass up in the 3500 rpm range in overdrive, I see 85 psi total and 54 psi between stages.

Atmospheric conditions in Las Vegas usually hover right around 14.5 psi.


(85 psi + 14.5 psi) / 14.5 psi = 6.86 overall PR

HT4B (54 psi + 14.5 psi)/ 14.5 psi = 4.72 PR

6.86/4.72 = 1.45 PR for He351 secondary turbo

1.45 * 14.5 - 14.5 = 6.57 or about 7 psi if run at atmospheric conditions.


Yep, that stock ported internal wastegate seems to be doing just fine at controlling the second stage turbo speed.
Click to expand...

My GT3782R/GTX4202R twins are similar in numbers. At 80 psig manifold, I'm around 40 psig on the primary. About 6.48:1 overall, 3.73:1 primary, 1.73:1 secondary. When I was max 60 psi, the PR's remained very much the same.
 
Big Blue24 said:
Where did you come up with 14.17? I just checked the current weather in Fairbanks, AK and the barometer is 29.53" that equates to 14.504 psi. It looks like you have a low pressure storm system blowing through so that is probably a little lower than your typical pressure.

Also, looking at your numbers, your twin setup only makes 50psi max boost on the boost gauge? 71mm over 88mm twins? Sounds like you have a bad boost leak or no fuel.
Click to expand...

I realize right now that is what it is. Im just saying in normal Summer months. That is what it usally come up with for 1000 ft.
I have no fuel. i just wanted to see where I am currently at. I realize my setup isnt perfect right now but it will be. Single pump with 60 overs is not enough.
What I dont understand is the final psi number. What does it mean?

Thanks
 
RIGHTEYEBLIND said:
I realize right now that is what it is. Im just saying in normal Summer months. That is what it usally come up with for 1000 ft.
I have no fuel. i just wanted to see where I am currently at. I realize my setup isnt perfect right now but it will be. Single pump with 60 overs is not enough.
What I dont understand is the final psi number. What does it mean?

Thanks
Click to expand...



The final PSI number comes from calculating the pressure ratio of the top turbo, in my case 1.45. Then plugging that pressure ratio into a short formula to see what that pressure ratio would be equivalent to in gauge pressure PSI if it was running as a single turbo. The single turbo equivalent number is just a reference point for comparison because most of us are familiar with single turbo boost numbers, not pressure ratio numbers.

For example, almost anyone knows that an HX35 is close to its limit when pushing 35-40 psi as a single turbo. Almost no one could tell you off the top of their head that normal pressure ratio limit for a HX35 is 3.4 to 3.8.
 
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