compound turbo design questions
11-18-2013, 03:43 PM
#16
DTR 1st Sergeant
I removed the restrictions a little at a time including all areas through the air path. New CAC, intake horn, Glacier intake cover with grid delete, some intake porting. Some of the ideas of the CAC are not well understood. I see any manner of blanket statements of "stock CAC is good to xx HP" without regard to environmental conditions.
CAC manufacture is tricky. A lot of things to consider. Airflow through the core: It has to have a certain amount of dwell time to allow the air to cool, but not so much that the CAC is a restriction to itself. It has to have enough surface area to do the job. Of course, it also can't be blocking too much airflow to the radiator either.
One of the things I like to point out on the stock CAC (let's not even go to the plastic caps) is that the CAC is also a heat sink. Yes, it takes the heat from compressed air and exchanges that heat to the atmospere. (simply stated) the stock CAC with thin metal has a limited capacity to xfer that heat compared to aftermarkets. If you are just cruising along the road, you'll never see it. Do some sled pulls or drags or dynos and all of a sudden the CAC is heated beyond the capacity to cool the compressed air sufficiently. A before and after test was illuminating for me. On the old 35/3B twins and stock CAC, after a couple of dyno pulls, you could not touch the driver's side of the CAC it was so hot. Put in the aftermarket, after several pulls the drivers side was warm, but touchable. How much cooler do you think the air was? The HP changes went up with a CAC as well.
That does not mean that I am recommending everyone go out and buy a CAC. Everything has it's place. Also, aftermarket CAC's tend to flow about ~30% more CFM on average over stock.
CAC manufacture is tricky. A lot of things to consider. Airflow through the core: It has to have a certain amount of dwell time to allow the air to cool, but not so much that the CAC is a restriction to itself. It has to have enough surface area to do the job. Of course, it also can't be blocking too much airflow to the radiator either.
One of the things I like to point out on the stock CAC (let's not even go to the plastic caps) is that the CAC is also a heat sink. Yes, it takes the heat from compressed air and exchanges that heat to the atmospere. (simply stated) the stock CAC with thin metal has a limited capacity to xfer that heat compared to aftermarkets. If you are just cruising along the road, you'll never see it. Do some sled pulls or drags or dynos and all of a sudden the CAC is heated beyond the capacity to cool the compressed air sufficiently. A before and after test was illuminating for me. On the old 35/3B twins and stock CAC, after a couple of dyno pulls, you could not touch the driver's side of the CAC it was so hot. Put in the aftermarket, after several pulls the drivers side was warm, but touchable. How much cooler do you think the air was? The HP changes went up with a CAC as well.
That does not mean that I am recommending everyone go out and buy a CAC. Everything has it's place. Also, aftermarket CAC's tend to flow about ~30% more CFM on average over stock.
11-18-2013, 09:03 PM
#17
Registered User
You design for the amount of HP you want. If you want 600hp, then you design around that aspect. You'll need xxx amount of air in lbs/min to reach that goal and xxx amount of fuel. Turbine wheels do get tricky, but with Garrett's they flow much more and are very light compared to BW journal type chargers which give them much better spool characteristics. The only downside to Garrett's are the waste gates, that is why you see folks run external gates. So much info goes into the design aspect, It's a little over my head. I pick up what I can when I can and take it as a grain of salt. Many different ways to skin a cat, so to speak.
Just read more of the previous post and Soulezoo is spot on.
Just read more of the previous post and Soulezoo is spot on.
11-18-2013, 09:20 PM
#19
Registered User
To remove the restriction you work on the intake and exhaust side. CAC, Intake horn, ported Head, cam, and exhaust manifold, turbine size, A/R of the turbine. Restriction on the exhaust side is measured by drive pressure. I dropped 4psi of boost with just a cam change. Added 80hp sticks and gained 4 psi back. More air, more fuel and the bottle neck is back...LOL You fix one restriction, add fuel, you get another restriction point. If your drive pressure get's to high, you increase your turbine A/R.
11-18-2013, 09:24 PM
#20
Registered User
No reason to stop commenting. Just remember the one thing Soulezoo said, Some folks have different ideas and can lead you in the wrong direction. So take every opinion with a grain of salt. The ones that are more than likely true will be validated by other folks. I have had a few of those different opinions. I am not saying that they are wrong. Just different and don't think they will give me the results I am shooting for.
11-18-2013, 09:28 PM
#21
Registered User
By the way, have fun with the new set you ordered. I unfortunately have to wait. Wife took my funds to use elsewhere. I thought I would have enough to continue on but, If the wife isn't happy, nobody is happy.
11-19-2013, 08:41 AM
#22
DTR 1st Sergeant
How did you remove 18 psi of restriction? Also I was [blissfully] unaware of the charge air cooler not being able to cool much beyond the stock charger output? My wallet won't like that... Oh well. I have run lots of numbers from examples guys wrote in on compd and it always seems that at the top end the turbos are not balanced (primary doing most of the work) BUT that there can be good linearity displayed on the secondary both before and after the gate setpoint is exceeded. But not a lot of turbo systems seemed to show this. Also have to have multiple data points recorded to see this obviously, and record above and below the psi setpoint of the gate.
It has been pointed out that on a compound system that the ratios between secondary and primary are more important than the actual gauge pressure on the interstage and the overall boost pressure and apparently that is true in that if a person thinks the primary or secondary is doing more than it should the only real way to see that is to do those calculations otherwise can't really tell. Still kind of confused about how to properly size a twin set properly. Say I [think] I would like to have 600 hp and 1200 torque and I mostly use the truck for daily driving and towing a 10000 lb fifth wheel. Also say that I don't ever use the truck for racing or sled pulling. And that I would like to keep the EGTs as cool as possible for engine longevity. And go even further to say that I just bought a set of BBi Stage 1 injectors which are around 90 hp or thereabouts and that I may consider a dual pump setup in the future so that fuel should [theoretically?] not be much of a problem. Also say that I have EFI Live so getting the tuning right should not be too difficult either.
So in this theoretical desired application what would be best selection for the turbos? Assuming BB Garretts, would that be the GT3582R over the GT4202R or the 3788 over the 4202? Or a bigger primary?
It has been pointed out that on a compound system that the ratios between secondary and primary are more important than the actual gauge pressure on the interstage and the overall boost pressure and apparently that is true in that if a person thinks the primary or secondary is doing more than it should the only real way to see that is to do those calculations otherwise can't really tell. Still kind of confused about how to properly size a twin set properly. Say I [think] I would like to have 600 hp and 1200 torque and I mostly use the truck for daily driving and towing a 10000 lb fifth wheel. Also say that I don't ever use the truck for racing or sled pulling. And that I would like to keep the EGTs as cool as possible for engine longevity. And go even further to say that I just bought a set of BBi Stage 1 injectors which are around 90 hp or thereabouts and that I may consider a dual pump setup in the future so that fuel should [theoretically?] not be much of a problem. Also say that I have EFI Live so getting the tuning right should not be too difficult either.
So in this theoretical desired application what would be best selection for the turbos? Assuming BB Garretts, would that be the GT3582R over the GT4202R or the 3788 over the 4202? Or a bigger primary?
Given what you want to use it for, I would suggest a gt3788r stage 3 (the 3788's are not all made the same and Tom knows what to do) over a GT4508r. The 3788 will use a .89 A/R internally wastegated EH; the 4508 can get by with a 1.15 A/R EH. That will be a tight set and you'll have some higher drive pressure on the top, but you'll spool much sooner and help that torque number you are trying to hit. Otherwise you can go a .99 A/R and 1.25 A/R and that'll relieve the high end drive pressure at the expense of spool. But rev gain is better after about 2800 rpm. You'll want a CAC to go with this (that's a lot of air).
Hope that helps.
11-19-2013, 08:47 AM
#23
DTR 1st Sergeant
Further comment to the above--
The EH's I listed for the 3788r are internally wastegated. A weak point for our use is that wastegate as it is on the small side. It is perfect for it's originally intended use, but not ideal for twins. So, you can either leave it alone and live with the drive pressure, or disable it and use a (recommended here) 44mm external gate.
The EH's I listed for the 3788r are internally wastegated. A weak point for our use is that wastegate as it is on the small side. It is perfect for it's originally intended use, but not ideal for twins. So, you can either leave it alone and live with the drive pressure, or disable it and use a (recommended here) 44mm external gate.
11-19-2013, 08:57 AM
#24
DTR 1st Sergeant
No reason to stop commenting. Just remember the one thing Soulezoo said, Some folks have different ideas and can lead you in the wrong direction. So take every opinion with a grain of salt. The ones that are more than likely true will be validated by other folks. I have had a few of those different opinions. I am not saying that they are wrong. Just different and don't think they will give me the results I am shooting for.
To borrow a quote, my advise is worth exactly what you paid for it.
I don't go on compD much any more simply because there is so much bickering and it gets personal with the flame wars and it clouds what otherwise could be useful information. I don't have much use for an immature poster arguing about things he obviously knows little about.
So I perfer to be here with good friends!
11-19-2013, 08:59 AM
#25
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Thanks very much. Extremely helpful and much appreciated. Can Tom set me up with a non-gated turbine housing to properly utilize an external gate? I really did suspect a 3582 may be too tight on the turbine side but what I don't know is the extent external gating can adequately resolve the restriction. Some have said no and some have said yes it can. That is what confuses me about properly sizing compounds. Also intended usage as some really want to operate above 2800 rpm and make recommendations that way BUT the guy who DD and tows 14k with his truck just isn't operating that way...
Thanks for the advice.
Thanks for the advice.
11-19-2013, 02:36 PM
#26
DTR 1st Sergeant
Tom can do an awful lot of stuff. But I don't believe a non wastegated housing is an option. But ask Tom. He can even do hybrid turbos to suit the need. It is nothing to disable the wastegate however.
Frankly, if you have no intention of spinning the engine over factory redline (i.e. going 3500+ rpm) the factory wastegate is adequate. Not ideal, but adequate.
It is not only the turbine side of the 35 that is a restriction, but the compressor side as well. I like that gtx35 a lot, but don't recommend it over say 600-650hp in twins. It is a super fast spooling turbo though and can handle some serious abuse. I like it as a single a lot better than the 37xx series. If you are in that 600-650 range, the gtx3582 over gt4202 is a wicked tow/street set up that will light faster than most singles.
Anyway, I am looking at your setup as a DD/towing/street fun setup more than a race/dyno/pulling setup. So the bias is toward the low end/midrange rather than mid/high range.
Good luck!
Frankly, if you have no intention of spinning the engine over factory redline (i.e. going 3500+ rpm) the factory wastegate is adequate. Not ideal, but adequate.
It is not only the turbine side of the 35 that is a restriction, but the compressor side as well. I like that gtx35 a lot, but don't recommend it over say 600-650hp in twins. It is a super fast spooling turbo though and can handle some serious abuse. I like it as a single a lot better than the 37xx series. If you are in that 600-650 range, the gtx3582 over gt4202 is a wicked tow/street set up that will light faster than most singles.
Anyway, I am looking at your setup as a DD/towing/street fun setup more than a race/dyno/pulling setup. So the bias is toward the low end/midrange rather than mid/high range.
Good luck!
11-19-2013, 04:24 PM
#27
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That's what I was thinking on the GTX3582 over the GT4202. For the way I use my truck that would be an awesome setup. Wife says I drive like an old grandpa she's prolly right I guess. Been looking at the Helmann CAC, billet air inlet, and valve cover (sweet looking piece there) likely going to abuse the card some more on those... Just for discussion what about a 4718 under that GTX3582R? Can 90 horse injectors and dual pumps keep it spinning? Another opinion welcome on this one...
11-19-2013, 04:35 PM
#28
DTR 1st Sergeant
Not a good setup. The 47 is too big for the 35. For that matter, 90 hp stix are too small for the 47... you couldn't fully utilize it. 120's at a bare minimum, 150's more like it.
That 47 is a very big turbo and can be made to fit... but it is very tight.
Realistically, everything revolves around the injector choice here. The 3788 over 4508 is a perfect fit.
That 47 is a very big turbo and can be made to fit... but it is very tight.
Realistically, everything revolves around the injector choice here. The 3788 over 4508 is a perfect fit.
11-19-2013, 05:17 PM
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From a drive pressure point of view, would the 3788/4508 be better than the 3582/4202? As long as the 3788 will spin up pretty well with some 90 horse injectors? Kind of working the DD/tow setup more. Sorry for the 20 questions but due to cost would like to get this right the first time. Thanks!
11-19-2013, 07:17 PM
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To remove the restriction you work on the intake and exhaust side. CAC, Intake horn, ported Head, cam, and exhaust manifold, turbine size, A/R of the turbine. Restriction on the exhaust side is measured by drive pressure. I dropped 4psi of boost with just a cam change. Added 80hp sticks and gained 4 psi back. More air, more fuel and the bottle neck is back...LOL You fix one restriction, add fuel, you get another restriction point. If your drive pressure get's to high, you increase your turbine A/R.