Page 4 of 6 FirstFirst 123456 LastLast
Results 61 to 80 of 108

Thread: Intake/Exhaust Pressure Ratio's - what's the big deal?

  1. #61
    Super Moderator Turbo Mopar Staff contraption22's Avatar
    Join Date
    Dec 2005
    Location
    Havertown, PA
    Posts
    9,517

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    Quote Originally Posted by acannell View Post
    im not sure if it was posted in one of these TM threads probably
    .
    It's stickies, but also in post #5 of this thread.
    Mike Marra
    1986 Plymouth Horizon GLMF "The Contraption" < entertaining sponsorship offers
    Project Log:
    http://www.turbo-mopar.com/forums/showthread.php?69708-The-Contraption-2013-14&highlight=

  2. #62
    Moderator Turbo Mopar Staff Force Fed Mopar's Avatar
    Join Date
    Dec 2005
    Location
    Greenville/Spartanburg SC area
    Posts
    7,557

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    Seems to me like the wastegate is the area to look at to reduce the drive pressure ratio without changing the turbo. Either in porting the internal wastegate hole or by adding an external wg that flows more.

    As I asked earlier, what if (in theoretical design, not sure if it is actually possible) you could get a header and external wg ( or two) that would flow enough exhaust once open to lower the ratio below 1:1? Is this still improving things, or is it reducing the turbine drive pressure and causing boost stability issues?
    Rob M.
    '89 Turbo GTC

    2.5 TIII stroker, 568 w/ OBX and 3.77 FD

  3. #63
    Hybrid booster
    Join Date
    Dec 2008
    Location
    United States
    Posts
    857

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    Quote Originally Posted by Shadow View Post
    Regardless, Lag does NOT have to be a big concern IF you do it Right
    Well said !.. in addition "or drive it right!"



    There was also mention within the thread about opening the WG hole to reduce back pressure.
    This is only true when the demanded exhaust flow exceeds available flow across the scroll area plus the WG hole, with the flapper near or at full extension.
    Otherwise, all that's accomplished by doing so (opening the WG hole) is altering the operating position of the valve because the boost will learn to close the valve, to obtain the same boost previously realized with the smaller hole.
    Therefore, depending on the boost being used and the resulting exhaust demands, you end up with the same back pressure until the turbine limit is exceeded.


    This leads into the turbine housing 'game'.
    The game consists of where the flow is desired 'WG/bypass OR turbine scroll'?
    Imagine that if a very small turbine wheel is used with a stock .48 turbine housing, the flow demand will shift to the WG hole because the scroll housing area and related exducer diameter will not support the flow alone.
    Likewise, the reflective approach is a larger housing and wheel which now minimizes the WG flow demand because the scroll area can now supports the required flow and excessive WG porting cannot be completely justified.
    This is ultimately the difference in approach when comparing the 2.2 of "yesteryear" to the SRT 2.4 of recent year.
    One realizes higher BP at low RPM to obtain quick response BUT minimizes upper RPM restriction when the WG opens.
    The other maintains lower BP throughout the RPM range and relies on minimal WG activity to control the target boost level.

    Two different approaches that can be set up in a way that produce the same exhaust BP levels but with completely different boost response curves.
    Which approach is required is largely dictated by the size (area and wheel mass) of the compressor and the energy required to get the process started and maintained.
    Last edited by 5DIGITS; 12-21-2014 at 12:45 AM.

  4. #64
    turbo addict
    Join Date
    Dec 2011
    Location
    Hemet,CA
    Posts
    1,636

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    Quote Originally Posted by Force Fed Mopar View Post
    Seems to me like the wastegate is the area to look at to reduce the drive pressure ratio without changing the turbo. Either in porting the internal wastegate hole or by adding an external wg that flows more.

    As I asked earlier, what if (in theoretical design, not sure if it is actually possible) you could get a header and external wg ( or two) that would flow enough exhaust once open to lower the ratio below 1:1? Is this still improving things, or is it reducing the turbine drive pressure and causing boost stability issues?
    Answering this sort of question in a way that can direct design requires more formal analysis than I've ever seen on TM or TD. I dont think we're there yet. When you see overlaid efficiency lines on compressor AND turbine maps linking the two at certain operating points then we're there. Never seen that on an internet forum.

    But to speak about it in the usual generalities, theres no such thing as "turbine drive pressure". There is pressure drop across the turbine, and mass flow rate through the turbine. Those two things generate the shaft power to drive the compressor. If the post turbine restriction is reduced to 0 and you have essentially atmospheric right at the turbine blades at the output, I dont see why you wouldn't be able to continue to modulate turbine power by bypassing exhaust around it. Less gas through the turbine = less power. I think any sort of boost control stability problems are going to have a more complex cause.

    To prove this you could split the exhaust stream in two and run two turbos each at half the power. So there shouldn't be some reason you cant control shaft power.

  5. #65
    turbo addict
    Join Date
    Apr 2009
    Location
    Detroit, MI
    Posts
    1,770

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    Quote Originally Posted by acannell View Post
    Answering this sort of question in a way that can direct design requires more formal analysis than I've ever seen on TM or TD. I dont think we're there yet. When you see overlaid efficiency lines on compressor AND turbine maps linking the two at certain operating points then we're there. Never seen that on an internet forum.

    But to speak about it in the usual generalities, theres no such thing as "turbine drive pressure". There is pressure drop across the turbine, and mass flow rate through the turbine. Those two things generate the shaft power to drive the compressor. If the post turbine restriction is reduced to 0 and you have essentially atmospheric right at the turbine blades at the output, I dont see why you wouldn't be able to continue to modulate turbine power by bypassing exhaust around it. Less gas through the turbine = less power. I think any sort of boost control stability problems are going to have a more complex cause.

    To prove this you could split the exhaust stream in two and run two turbos each at half the power. So there shouldn't be some reason you cant control shaft power.
    As stated earlier and in your last paragraph, twin scroll technology is pretty much 2 turbine housings, powering one compressor wheel.
    [SIGPIC][/SIGPIC]

  6. #66
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
    Join Date
    Dec 2006
    Location
    Aubigny, Manitoba, Canada
    Posts
    5,088

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    Quote Originally Posted by Force Fed Mopar View Post
    Seems to me like the wastegate is the area to look at to reduce the drive pressure ratio without changing the turbo. Either in porting the internal wastegate hole or by adding an external wg that flows more.

    As I asked earlier, what if (in theoretical design, not sure if it is actually possible) you could get a header and external wg ( or two) that would flow enough exhaust once open to lower the ratio below 1:1? Is this still improving things, or is it reducing the turbine drive pressure and causing boost stability issues?
    Any attempt to increase W/G flow will result in lower boost, there are No two ways around it. The only exception I know of is Dedicated W/G positioning using a deliberately Smaller turbine housing/ wheel that normal to get Great response down low, then Good top end flow when the exhaust drive pressure overruns the turbine and flows through the Dedicated W/G. AFAIK this will Not Increase top end power significantly over a properly sized turbine application, but it Will give Better response down low.

    Robert Mclellan
    http://www.youtube.com/watch?v=wambNdfnu5M
    10.04 @ 143.28mph (144.82 highest mph)
    Worlds fastest 8v MTX Shelby Charger
    Manitoba's Fastest 4cyl!
    8 valve, No Nitrous!
    New clutch combo is the SH!T!

  7. #67
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
    Join Date
    Dec 2006
    Location
    Aubigny, Manitoba, Canada
    Posts
    5,088

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    Quote Originally Posted by 5DIGITS View Post
    There was also mention within the thread about opening the WG hole to reduce back pressure.
    This is only true when the demanded exhaust flow exceeds available flow across the scroll area plus the WG hole, with the flapper near or at full extension.
    Otherwise, all that's accomplished by doing so (opening the WG hole) is altering the operating position of the valve because the boost will learn to close the valve, to obtain the same boost previously realized with the smaller hole.
    Therefore, depending on the boost being used and the resulting exhaust demands, you end up with the same back pressure until the turbine limit is exceeded.


    This leads into the turbine housing 'game'.
    The game consists of where the flow is desired 'WG/bypass OR turbine scroll'?
    Imagine that if a very small turbine wheel is used with a stock .48 turbine housing, the flow demand will shift to the WG hole because the scroll housing area and related exducer diameter will not support the flow alone.
    Likewise, the reflective approach is a larger housing and wheel which now minimizes the WG flow demand because the scroll area can now supports the required flow and excessive WG porting cannot be completely justified.
    This is ultimately the difference in approach when comparing the 2.2 of "yesteryear" to the SRT 2.4 of recent year.
    One realizes higher BP at low RPM to obtain quick response BUT minimizes upper RPM restriction when the WG opens.
    The other maintains lower BP throughout the RPM range and relies on minimal WG activity to control the target boost level.

    Two different approaches that can be set up in a way that produce the same exhaust BP levels but with completely different boost response curves.
    Which approach is required is largely dictated by the size (area and wheel mass) of the compressor and the energy required to get the process started and maintained.
    Agreed, and back to the comment I made on Drive pressure vs lag. (now that I can type freely )

    My first post (the novel) was an Inspired Mona Lisa, unfortunately that only happens once, so you guys will have to make due with the dummied down version.

    In a nut shell, If you attempt to use A/R and turbine wheel size to correct drive pressure, you Will most definitely Suffer from turbo Lag. This is what most have done and were doing back when I first got involved with turbocharging.

    So what did I do? I decide to use the Smallest turbine housing/ wheel combo I could in order to achieve desired Power level (Pressure differential be damned!) but make the Intake and exhaust Outlet as Efficient as I possibly could.

    Did I Know I was heading down the path to 1:1 differential with Phenomenal street drivability? Nope! Had no clue. Until I installed the drive pressure gauge I would have thought the drive pressure in the Charger would have been at Least 2:1. I was Shocked to say the least, but it showed me that Not only does it work, it works Better than I had Ever imagined!

    Remember, when I ran the 4" intake everyone said it was severe overkill. When I showed the 4" downpipe, same response. When I said I could make over 500WHP from the 9cm turbine housing on the holset (.65 A/R) they all said it was Way too small and that I would Lose top end power because of the tiny turbine housing and wheel.

    Pretty sure, even to this day, that the Charger has one of, if not The Higher top end 1/4 mile Charger of Any 8v TD/ TM I know of. Add to this that the transient response is so mind boggling to those who I have take for rides that they say the car has No Lag, and How is this Possible.

    So, Again, as much as most like to Think the charger is a laggy Drag car, it is actually the Complete opposite. Which Proves that you Can have a 1:1 differential and Great transient response IF you do it Right! (and yes, Know how to Drive a turbo car! )

    Robert Mclellan
    http://www.youtube.com/watch?v=wambNdfnu5M
    10.04 @ 143.28mph (144.82 highest mph)
    Worlds fastest 8v MTX Shelby Charger
    Manitoba's Fastest 4cyl!
    8 valve, No Nitrous!
    New clutch combo is the SH!T!

  8. #68
    Moderator Turbo Mopar Staff Force Fed Mopar's Avatar
    Join Date
    Dec 2005
    Location
    Greenville/Spartanburg SC area
    Posts
    7,557

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    Quote Originally Posted by Shadow View Post
    Agreed, and back to the comment I made on Drive pressure vs lag. (now that I can type freely )

    My first post (the novel) was an Inspired Mona Lisa, unfortunately that only happens once, so you guys will have to make due with the dummied down version.

    In a nut shell, If you attempt to use A/R and turbine wheel size to correct drive pressure, you Will most definitely Suffer from turbo Lag. This is what most have done and were doing back when I first got involved with turbocharging.

    So what did I do? I decide to use the Smallest turbine housing/ wheel combo I could in order to achieve desired Power level (Pressure differential be damned!) but make the Intake and exhaust Outlet as Efficient as I possibly could.

    Did I Know I was heading down the path to 1:1 differential with Phenomenal street drivability? Nope! Had no clue. Until I installed the drive pressure gauge I would have thought the drive pressure in the Charger would have been at Least 2:1. I was Shocked to say the least, but it showed me that Not only does it work, it works Better than I had Ever imagined!

    Remember, when I ran the 4" intake everyone said it was severe overkill. When I showed the 4" downpipe, same response. When I said I could make over 500WHP from the 9cm turbine housing on the holset (.65 A/R) they all said it was Way too small and that I would Lose top end power because of the tiny turbine housing and wheel.

    Pretty sure, even to this day, that the Charger has one of, if not The Higher top end 1/4 mile Charger of Any 8v TD/ TM I know of. Add to this that the transient response is so mind boggling to those who I have take for rides that they say the car has No Lag, and How is this Possible.

    So, Again, as much as most like to Think the charger is a laggy Drag car, it is actually the Complete opposite. Which Proves that you Can have a 1:1 differential and Great transient response IF you do it Right! (and yes, Know how to Drive a turbo car! )
    And this is still on the stock exhaust manifold, correct? And stock Holset internal WG?
    Rob M.
    '89 Turbo GTC

    2.5 TIII stroker, 568 w/ OBX and 3.77 FD

  9. #69
    turbo addict
    Join Date
    Apr 2009
    Location
    Detroit, MI
    Posts
    1,770

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    I know Rob still runs the ported stocker, and I "think" the internal gate too.
    [SIGPIC][/SIGPIC]

  10. #70
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
    Join Date
    Dec 2006
    Location
    Aubigny, Manitoba, Canada
    Posts
    5,088

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    Quote Originally Posted by Force Fed Mopar View Post
    And this is still on the stock exhaust manifold, correct? And stock Holset internal WG?
    Correct. My own stock ported exhaust mani and stock untouched Holset W/G hole with tension on W/G actuator set to minimum.

    Robert Mclellan
    http://www.youtube.com/watch?v=wambNdfnu5M
    10.04 @ 143.28mph (144.82 highest mph)
    Worlds fastest 8v MTX Shelby Charger
    Manitoba's Fastest 4cyl!
    8 valve, No Nitrous!
    New clutch combo is the SH!T!

  11. #71
    turbo addict
    Join Date
    Nov 2006
    Location
    san diego, california
    Posts
    1,548

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    stock untouched Holset W/G hole
    but I do think you have hinted to the fact that you may need to port the wastegate hole soon, as you seamed to have a small amount of boost creep when running the 12" long 4" dump...

  12. #72
    turbo addict Pat's Avatar
    Join Date
    Dec 2005
    Location
    Rockville, MD
    Posts
    3,801

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    Rob...where are you tapped for pre turbo pressure? At the manifold collector?

  13. #73
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
    Join Date
    Dec 2006
    Location
    Aubigny, Manitoba, Canada
    Posts
    5,088

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    Quote Originally Posted by OmniLuvr View Post
    but I do think you have hinted to the fact that you may need to port the wastegate hole soon, as you seamed to have a small amount of boost creep when running the 12" long 4" dump...
    It Will creep at lower boost with the dump open. (below 25psi) but I only open the dump at the track, so really not an issue. I am considering porting it to bring down my minimum street boost setting Back to around 18psi. Right now it's around 22 and while that's fine for 93-94 octane, I get some knock on 91 and 91 is becoming the common Premium fuel around here.

    - - - Updated - - -

    Quote Originally Posted by Pat View Post
    Rob...where are you tapped for pre turbo pressure? At the manifold collector?
    Yes, manifold collector right at the flange to the turbo.

    Robert Mclellan
    http://www.youtube.com/watch?v=wambNdfnu5M
    10.04 @ 143.28mph (144.82 highest mph)
    Worlds fastest 8v MTX Shelby Charger
    Manitoba's Fastest 4cyl!
    8 valve, No Nitrous!
    New clutch combo is the SH!T!

  14. #74
    turbo addict
    Join Date
    Nov 2006
    Location
    san diego, california
    Posts
    1,548

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    It Will creep at lower boost with the dump open. (below 25psi) but I only open the dump at the track, so really not an issue
    gotcha! I remember you talking about it a while ago, it was in a good thread where I learned a lot of things, very good info from you, just cant remember which one it was? (prob 4 years ago?)

  15. #75
    Moderator Turbo Mopar Staff Force Fed Mopar's Avatar
    Join Date
    Dec 2005
    Location
    Greenville/Spartanburg SC area
    Posts
    7,557

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    So the main factor in drive pressure seems to indeed be turbine selection...
    Rob M.
    '89 Turbo GTC

    2.5 TIII stroker, 568 w/ OBX and 3.77 FD

  16. #76
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
    Join Date
    Dec 2006
    Location
    Aubigny, Manitoba, Canada
    Posts
    5,088

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    Quote Originally Posted by Force Fed Mopar View Post
    So the main factor in drive pressure seems to indeed be turbine selection...
    Quote Originally Posted by BoostedDrummer View Post
    Doesn't a higher pressure in the exhaust manifold spool the turbo up faster due to the high pressure trying to shoot out the turbine? Basic law of fluid dynamics is that high pressure will always try to flow to an area of lower pressure, so, that being said, wouldn't all of that pressure trying to escape into the exhaust downpipe have a faster velocity?
    THIS^^^^^

    Is what I would consider the main factor in getting and keeping your drive pressure in check. You want the Greatest pressure differential right after the turbine. So whatever your drive pressure is (pre-turbine), let's say 20psi, if you could, you would shoot for Zero psi in the downpipe.

    As the downpipe back pressure increases, the exhaust mani drive pressure Will Increase exponentially, causing the entire system to "back up" and lose power.

    Just keep in mind that you want to attain this while keeping the intake vs exhaust mani ratio as close to 1:1 as possible.

    And for those who are wondering, 1.5 : 1 is Not that bad (there are Freaks out there that think 6 : 1 is OK lol)

    Robert Mclellan
    http://www.youtube.com/watch?v=wambNdfnu5M
    10.04 @ 143.28mph (144.82 highest mph)
    Worlds fastest 8v MTX Shelby Charger
    Manitoba's Fastest 4cyl!
    8 valve, No Nitrous!
    New clutch combo is the SH!T!

  17. #77
    turbo addict
    Join Date
    Jan 2006
    Location
    Hazelwood, MO
    Posts
    6,566

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    Keep in mind that the turbine housing A/R ratio is only part of the equation when talking about turbine efficiency and how it uses the mass flow. The design of the turbine nozzle affects the angle and the velocity at which the flow hits the turbine blades. This can have a significant impact on turbo response and turbine flow/efficiency.

    The turbine wheel itself is also very important as the aerodynamics of the blades can have a significant impact on mass flow out of the turbine, how efficient the gas can do work to the turbine, turbo response...and I'm sure I'm forgetting something right now.

    Anyway, the point I'm trying to make is the turbine of a turbo is a system, just like everything else in the engine.

  18. #78
    turbo addict
    Join Date
    Dec 2011
    Location
    Hemet,CA
    Posts
    1,636

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    Quote Originally Posted by Reaper1 View Post
    Keep in mind that the turbine housing A/R ratio is only part of the equation when talking about turbine efficiency and how it uses the mass flow. The design of the turbine nozzle affects the angle and the velocity at which the flow hits the turbine blades. This can have a significant impact on turbo response and turbine flow/efficiency.

    The turbine wheel itself is also very important as the aerodynamics of the blades can have a significant impact on mass flow out of the turbine, how efficient the gas can do work to the turbine, turbo response...and I'm sure I'm forgetting something right now.

    Anyway, the point I'm trying to make is the turbine of a turbo is a system, just like everything else in the engine.
    Yes good point. Has anyone seen a turbine/housing map for any of our typical turbos? I know there are compressor maps but Ive not seen a turbine map.

  19. #79
    turbo addict
    Join Date
    Jan 2006
    Location
    Hazelwood, MO
    Posts
    6,566

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    The Holset EFR series has both their compressor and turbine maps on their website last I checked.

  20. #80
    turbo addict
    Join Date
    Apr 2009
    Location
    Detroit, MI
    Posts
    1,770

    Re: Intake/Exhaust Pressure Ratio's - what's the big deal?

    I'm still surprised that no one has really touched the subject on twin scroll stuff.
    [SIGPIC][/SIGPIC]

Page 4 of 6 FirstFirst 123456 LastLast

Similar Threads

  1. Replies: 26
    Last Post: 08-12-2014, 05:30 PM
  2. Exhaust pressure
    By Force Fed Mopar in forum Exhaust
    Replies: 18
    Last Post: 01-30-2013, 09:20 AM
  3. Replies: 7
    Last Post: 12-11-2008, 07:34 PM
  4. Exhaust tuning, pressure relief?
    By RoadWarrior222 in forum Exhaust
    Replies: 6
    Last Post: 08-23-2007, 10:14 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •