Tuning Twins

5.9 Cummins Fan

5.9 Cummins Fan

Gearhead
Joined
Mar 16, 2009
Messages
444
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)

Primary Boost------PR....................Secondary Boost------PR
1------------------1.08.................2---------------------1.07
2------------------1.16.................4---------------------1.138
3------------------1.24.................7---------------------1.258
4------------------1.32.................9---------------------1.30
5------------------1.40.................12--------------------1.40
6------------------1.48.................15--------------------1.4875
7------------------1.56.................18--------------------1.565
8------------------1.64.................21--------------------1.635
9------------------1.72.................25--------------------1.745
10-----------------1.80.................28--------------------1.80
11-----------------1.88.................32--------------------1.89
12-----------------1.96.................36--------------------1.98
13-----------------2.04.................40--------------------2.06
14-----------------2.12.................44--------------------2.13 *
15-----------------2.20.................48--------------------2.20 *
16-----------------2.28.................52--------------------2.26 *
17-----------------2.36.................57--------------------2.357
18-----------------2.44.................62--------------------2.44
19-----------------2.52.................67--------------------2.525
20-----------------2.60.................72--------------------2.60
So my stupid question is, say I want to have 65ish PSI how do you set the wastegates on each charger? I'm sure I'm making this way harder than I should, brain is on overload trying study for finals and mess with my truck, yada yada yada. Oh and the chargers are hx35/40 and s475. The three with the stars by them are PR's that are in or very near the best efficiency range of each charger, at least from the crappy map printouts i have for an s475 and hx40. Just a newbie looking for the wisdom of more experienced guys, thanks in advance
 
Last edited:
5.9 Cummins Fan said:
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)

Primary Boost------PR....................Secondary Boost------PR
1------------------1.08.................2---------------------1.07
2------------------1.16.................4---------------------1.138
3------------------1.24.................7---------------------1.258
4------------------1.32.................9---------------------1.30
5------------------1.40.................12--------------------1.40
6------------------1.48.................15--------------------1.4875
7------------------1.56.................18--------------------1.565
8------------------1.64.................21--------------------1.635
9------------------1.72.................25--------------------1.745
10-----------------1.80.................28--------------------1.80
11-----------------1.88.................32--------------------1.89
12-----------------1.96.................36--------------------1.98
13-----------------2.04.................40--------------------2.06
14-----------------2.12.................44--------------------2.13 *
15-----------------2.20.................48--------------------2.20 *
16-----------------2.28.................52--------------------2.26 *
17-----------------2.36.................57--------------------2.357
18-----------------2.44.................62--------------------2.44
19-----------------2.52.................67--------------------2.525
20-----------------2.60.................72--------------------2.60
So my stupid question is, say I want to have 65ish PSI how do you set the wastegates on each charger? I'm sure I'm making this way harder than I should, brain is on overload trying study for finals and mess with my truck, yada yada yada. Oh and the chargers are hx35/40 and s475. The three with the stars by them are PR's that are in or very near the best efficiency range of each charger, at least from the crappy map printouts i have for an s475 and hx40. Just a newbie looking for the wisdom of more experienced guys, thanks in advance
Click to expand...



Id start at 20psi for the top. Is your 475 gated?
 
75 comp 94 turbine, had a 0.8 A/R cast into compressor housing. It actually came off a big CAT engine and I got it for free. Had a lot of people tell me its junk and not even a BW, but it says Borg Warner right on the tag. Don't know exhaust housing size, but its not really big if I were to guess would be 25ish cm.
Thanks,
Sam
 
5.9 Cummins Fan said:
75 comp 94 turbine, had a 0.8 A/R cast into compressor housing. It actually came off a big CAT engine and I got it for free. Had a lot of people tell me its junk and not even a BW, but it says Borg Warner right on the tag. Don't know exhaust housing size, but its not really big if I were to guess would be 25ish cm.
Thanks,
Sam
Click to expand...



Do you know the serial numbers?
 
so just start with 20 secondary and 30 primary and just work from there like a crap shoot? Thought you could get them pretty close using regulated shop air then just fine tune them on the truck. Maybe I'm way off base. Thanks for giving me an idea bsmith, more info than I can get out the people in my neck of the woods
 
Last edited:
5.9 Cummins Fan said:
so just start with 20 secondary and 30 primary and just work from there like a crap shoot? Thought you could get them pretty close using regulated shop air then just fine tune them on the truck. Maybe I'm way off base. Thanks for giving me an idea bsmith, more info than I can get out the people in my neck of the woods
Click to expand...


Thats how you do it, go off shop air. Go ride, watch your gauges(dp and boost) see when their opening by watching dp drop. You want your drive pressure and total boost as close to 1:1 as possible.
 
Last edited:
5.9 Cummins Fan said:
75 comp 94 turbine, had a 0.8 A/R cast into compressor housing. It actually came off a big CAT engine and I got it for free. Had a lot of people tell me its junk and not even a BW, but it says Borg Warner right on the tag. Don't know exhaust housing size, but its not really big if I were to guess would be 25ish cm.
Thanks,
Sam
Click to expand...

what cat motor did it come off of? c12 or something?
 
So my stupid question is, say I want to have 65ish PSI how do you set the wastegates on each charger? I'm sure I'm making this way harder than I should, brain is on overload trying study for finals and mess with my truck, yada yada yada.
Click to expand...

Not a stupid question, and you're not overthinking things. First off, you're way ahead of most people who just say "set the secondary at twice the boost of the primary". However, as you know, boost ratios and PR are NOT the same.

I went through this about a year ago as well, with my 62/476 install. It's somewhat hard to find helpful, technically accurate information on tuning twins (at least from what I could find). Nonetheless, here's what I've found out on mine.

You're going about it right, in that you want each turbo to share half of the "work"...and this means running equal PRs. However, from what I've experienced, it's not possible for this to happen in reality. You can adjust the wastegate on the secondary so that PRs on the two turbos match at one condition, but they won't match at any of the other conditions.

Since the secondary begins to spool much faster, its boost climbs quickly to about 10 psi before the primary begins to make a pound or two. The secondary continues to build boost faster, up to the point that its wastegate cracks. When the wastegate opens on the secondary, the primary begins to pick up speed much quicker. This (obviously) is because the primary is now receiving a larger percentage of the exhaust flow, and it's "higher quality" exaust due to the higher temperature of the wastegated exhaust...it is also beginning to get into the mass flow rate of air where it was designed to operate.

Thus, when you reach this point, the primary now begins building boost much quicker than the secondary. As such, neither of the turbos spool linearly with respect to each other. The small one spools quicker at first, and tapers off as the wastegate cracks. The big one is slow at first, and gets a kick in the pants as the secondary's wastegate opens. Because of this non-linearity, I've not found a way to maintain a constant shared PR across the speed/load operating range of the engine.

The best I've been able to do, is to set the wastegate on the secondary such that you are at a 1:1 PR ratio with the two turbos at about 75 - 80% of full horsepower. This allows the small secondary to spool quickly and get you going. At full 100% hp, the primary will be doing more work than it should; however, for daily driving, this has worked better for me. It does make the primary have a higher PR than the secondary at WOT, but it allows the PRs to be more closely matched in the 40 - 75% throttle range where I normally tow/drive/need boost at.

For an all-out-best dyno number, it may be better to match PRs at 100% load, but I've found for a daily driver/work horse, a little lower does better. For what it's worth, with my ~650 hp worth of fueling, the 476 primary never sees much more than 25 psi on a WOT run. Thus, unless you are too heavily fueled for the set of twins you have, I don't think there is much tuning to be done with the wastegate setting on the primary...as long as you aren't letting it crack before 25 or 30 psi and "wasting" exhaust energy.

Again, the above info may or may not be accurate, and may not be the best way of doing things. It's just what I've found to be true with my limited knowledge and my setup.

--Eric
 
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5.9 Cummins Fan said:
Came off a 3406E
Click to expand...

cool thanks. im going to try and find one of those. even if i have to rebuild it, i like the idea of an internally gated 475. nice billet wheel and race cover would make an awesome primary. i have a 35/40 as well so i am very interested to see how you like it with a 475. any other ideas or suggestions for a primary that would run well with a 35/40, besides a bht3b, im all ears.
 
ENafziger said:
Not a stupid question, and you're not overthinking things. First off, you're way ahead of most people who just say "set the secondary at twice the boost of the primary". However, as you know, boost ratios and PR are NOT the same.

I went through this about a year ago as well, with my 62/476 install. It's somewhat hard to find helpful, technically accurate information on tuning twins (at least from what I could find). Nonetheless, here's what I've found out on mine.

You're going about it right, in that you want each turbo to share half of the "work"...and this means running equal PRs. However, from what I've experienced, it's not possible for this to happen in reality. You can adjust the wastegate on the secondary so that PRs on the two turbos match at one condition, but they won't match at any of the other conditions.

Since the secondary begins to spool much faster, its boost climbs quickly to about 10 psi before the primary begins to make a pound or two. The secondary continues to build boost faster, up to the point that its wastegate cracks. When the wastegate opens on the secondary, the primary begins to pick up speed much quicker. This (obviously) is because the primary is now receiving a larger percentage of the exhaust flow, and it's "higher quality" exaust due to the higher temperature of the wastegated exhaust...it is also beginning to get into the mass flow rate of air where it was designed to operate.

Thus, when you reach this point, the primary now begins building boost much quicker than the secondary. As such, neither of the turbos spool linearly with respect to each other. The small one spools quicker at first, and tapers off as the wastegate cracks. The big one is slow at first, and gets a kick in the pants as the secondary's wastegate opens. Because of this non-linearity, I've not found a way to maintain a constant shared PR across the speed/load operating range of the engine.

The best I've been able to do, is to set the wastegate on the secondary such that you are at a 1:1 PR ratio with the two turbos at about 75 - 80% of full horsepower. This allows the small secondary to spool quickly and get you going. At full 100% hp, the primary will be doing more work than it should; however, for daily driving, this has worked better for me. It does make the primary have a higher PR than the secondary at WOT, but it allows the PRs to be more closely matched in the 40 - 75% throttle range where I normally tow/drive/need boost at.

For an all-out-best dyno number, it may be better to match PRs at 100% load, but I've found for a daily driver/work horse, a little lower does better. For what it's worth, with my ~650 hp worth of fueling, the 476 primary never sees much more than 25 psi on a WOT run. Thus, unless you are too heavily fueled for the set of twins you have, I don't think there is much tuning to be done with the wastegate setting on the primary...as long as you aren't letting it crack before 25 or 30 psi and "wasting" exhaust energy.

Again, the above info may or may not be accurate, and may not be the best way of doing things. It's just what I've found to be true with my limited knowledge and my setup.

--Eric
Click to expand...

AWESOME post Eric!!!
 
ENafziger said:
Not a stupid question, and you're not overthinking things. First off, you're way ahead of most people who just say "set the secondary at twice the boost of the primary". However, as you know, boost ratios and PR are NOT the same.

I went through this about a year ago as well, with my 62/476 install. It's somewhat hard to find helpful, technically accurate information on tuning twins (at least from what I could find). Nonetheless, here's what I've found out on mine.

You're going about it right, in that you want each turbo to share half of the "work"...and this means running equal PRs. However, from what I've experienced, it's not possible for this to happen in reality. You can adjust the wastegate on the secondary so that PRs on the two turbos match at one condition, but they won't match at any of the other conditions.

Since the secondary begins to spool much faster, its boost climbs quickly to about 10 psi before the primary begins to make a pound or two. The secondary continues to build boost faster, up to the point that its wastegate cracks. When the wastegate opens on the secondary, the primary begins to pick up speed much quicker. This (obviously) is because the primary is now receiving a larger percentage of the exhaust flow, and it's "higher quality" exaust due to the higher temperature of the wastegated exhaust...it is also beginning to get into the mass flow rate of air where it was designed to operate.

Thus, when you reach this point, the primary now begins building boost much quicker than the secondary. As such, neither of the turbos spool linearly with respect to each other. The small one spools quicker at first, and tapers off as the wastegate cracks. The big one is slow at first, and gets a kick in the pants as the secondary's wastegate opens. Because of this non-linearity, I've not found a way to maintain a constant shared PR across the speed/load operating range of the engine.

The best I've been able to do, is to set the wastegate on the secondary such that you are at a 1:1 PR ratio with the two turbos at about 75 - 80% of full horsepower. This allows the small secondary to spool quickly and get you going. At full 100% hp, the primary will be doing more work than it should; however, for daily driving, this has worked better for me. It does make the primary have a higher PR than the secondary at WOT, but it allows the PRs to be more closely matched in the 40 - 75% throttle range where I normally tow/drive/need boost at.

For an all-out-best dyno number, it may be better to match PRs at 100% load, but I've found for a daily driver/work horse, a little lower does better. For what it's worth, with my ~650 hp worth of fueling, the 476 primary never sees much more than 25 psi on a WOT run. Thus, unless you are too heavily fueled for the set of twins you have, I don't think there is much tuning to be done with the wastegate setting on the primary...as long as you aren't letting it crack before 25 or 30 psi and "wasting" exhaust energy.

Again, the above info may or may not be accurate, and may not be the best way of doing things. It's just what I've found to be true with my limited knowledge and my setup.

--Eric
Click to expand...

Thanks a ton man
 
some 98 cummins said:
cool thanks. im going to try and find one of those. even if i have to rebuild it, i like the idea of an internally gated 475. nice billet wheel and race cover would make an awesome primary. i have a 35/40 as well so i am very interested to see how you like it with a 475. any other ideas or suggestions for a primary that would run well with a 35/40, besides a bht3b, im all ears.
Click to expand...

You could use a K31, HT60, GT4294, and probably a GT4202. Depends on what your wanting to do with the twins. I am going to run the hybrid until I have enough coin to get a bullseye s364 for my secondary.
 
tuning waist gate

How did your tuning relate to the boost from each turbo vs total boost?
I don't have a drive pressure gauge set up so I can only convey what I'm seeing boost wise.
I try to keep the secondary boost 4 psi higher than half to total. This seems to happen a about 40 psi & up.
That was the way it was explained to me .







QUOTE=ENafziger;1404736]Not a stupid question, and you're not overthinking things. First off, you're way ahead of most people who just say "set the secondary at twice the boost of the primary". However, as you know, boost ratios and PR are NOT the same.

I went through this about a year ago as well, with my 62/476 install. It's somewhat hard to find helpful, technically accurate information on tuning twins (at least from what I could find). Nonetheless, here's what I've found out on mine.

You're going about it right, in that you want each turbo to share half of the "work"...and this means running equal PRs. However, from what I've experienced, it's not possible for this to happen in reality. You can adjust the wastegate on the secondary so that PRs on the two turbos match at one condition, but they won't match at any of the other conditions.

Since the secondary begins to spool much faster, its boost climbs quickly to about 10 psi before the primary begins to make a pound or two. The secondary continues to build boost faster, up to the point that its wastegate cracks. When the wastegate opens on the secondary, the primary begins to pick up speed much quicker. This (obviously) is because the primary is now receiving a larger percentage of the exhaust flow, and it's "higher quality" exaust due to the higher temperature of the wastegated exhaust...it is also beginning to get into the mass flow rate of air where it was designed to operate.

Thus, when you reach this point, the primary now begins building boost much quicker than the secondary. As such, neither of the turbos spool linearly with respect to each other. The small one spools quicker at first, and tapers off as the wastegate cracks. The big one is slow at first, and gets a kick in the pants as the secondary's wastegate opens. Because of this non-linearity, I've not found a way to maintain a constant shared PR across the speed/load operating range of the engine.

The best I've been able to do, is to set the wastegate on the secondary such that you are at a 1:1 PR ratio with the two turbos at about 75 - 80% of full horsepower. This allows the small secondary to spool quickly and get you going. At full 100% hp, the primary will be doing more work than it should; however, for daily driving, this has worked better for me. It does make the primary have a higher PR than the secondary at WOT, but it allows the PRs to be more closely matched in the 40 - 75% throttle range where I normally tow/drive/need boost at.

For an all-out-best dyno number, it may be better to match PRs at 100% load, but I've found for a daily driver/work horse, a little lower does better. For what it's worth, with my ~650 hp worth of fueling, the 476 primary never sees much more than 25 psi on a WOT run. Thus, unless you are too heavily fueled for the set of twins you have, I don't think there is much tuning to be done with the wastegate setting on the primary...as long as you aren't letting it crack before 25 or 30 psi and "wasting" exhaust energy.

Again, the above info may or may not be accurate, and may not be the best way of doing things. It's just what I've found to be true with my limited knowledge and my setup.

--Eric[/QUOTE]
 
doug60 said:
How did your tuning relate to the boost from each turbo vs total boost?
I don't have a drive pressure gauge set up so I can only convey what I'm seeing boost wise.
I try to keep the secondary boost 4 psi higher than half to total. This seems to happen a about 40 psi & up.
That was the way it was explained to me .





O

QUOTE=ENafziger;1404736]Not a stupid question, and you're not overthinking things. First off, you're way ahead of most people who just say "set the secondary at twice the boost of the primary". However, as you know, boost ratios and PR are NOT the same.

I went through this about a year ago as well, with my 62/476 install. It's somewhat hard to find helpful, technically accurate information on tuning twins (at least from what I could find). Nonetheless, here's what I've found out on mine.

You're going about it right, in that you want each turbo to share half of the "work"...and this means running equal PRs. However, from what I've experienced, it's not possible for this to happen in reality. You can adjust the wastegate on the secondary so that PRs on the two turbos match at one condition, but they won't match at any of the other conditions.

Since the secondary begins to spool much faster, its boost climbs quickly to about 10 psi before the primary begins to make a pound or two. The secondary continues to build boost faster, up to the point that its wastegate cracks. When the wastegate opens on the secondary, the primary begins to pick up speed much quicker. This (obviously) is because the primary is now receiving a larger percentage of the exhaust flow, and it's "higher quality" exaust due to the higher temperature of the wastegated exhaust...it is also beginning to get into the mass flow rate of air where it was designed to operate.

Thus, when you reach this point, the primary now begins building boost much quicker than the secondary. As such, neither of the turbos spool linearly with respect to each other. The small one spools quicker at first, and tapers off as the wastegate cracks. The big one is slow at first, and gets a kick in the pants as the secondary's wastegate opens. Because of this non-linearity, I've not found a way to maintain a constant shared PR across the speed/load operating range of the engine.

The best I've been able to do, is to set the wastegate on the secondary such that you are at a 1:1 PR ratio with the two turbos at about 75 - 80% of full horsepower. This allows the small secondary to spool quickly and get you going. At full 100% hp, the primary will be doing more work than it should; however, for daily driving, this has worked better for me. It does make the primary have a higher PR than the secondary at WOT, but it allows the PRs to be more closely matched in the 40 - 75% throttle range where I normally tow/drive/need boost at.

For an all-out-best dyno number, it may be better to match PRs at 100% load, but I've found for a daily driver/work horse, a little lower does better. For what it's worth, with my ~650 hp worth of fueling, the 476 primary never sees much more than 25 psi on a WOT run. Thus, unless you are too heavily fueled for the set of twins you have, I don't think there is much tuning to be done with the wastegate setting on the primary...as long as you aren't letting it crack before 25 or 30 psi and "wasting" exhaust energy.

Again, the above info may or may not be accurate, and may not be the best way of doing things. It's just what I've found to be true with my limited knowledge and my setup.

--Eric
Click to expand...
[/QUOTE]

4 psi over half is waaay off.
 
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