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Holset backpressure

Posted by jpmxrider489, Oct 1, 2020

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  1. jpmxrider489

    jpmxrider489 Supporting VIP

    Joined Apr 4, 2010
    pittsburgh, Pennsylvania
    I just got back from the dyno. And was told backpressre is the reason torque is dropping rapidly. So the turbo is a 7blade hx35 with a 16cm ported housing truly divided. How can someone solve back pressure?

    Attached Files:

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    Street Build 329  1

    1995 Eagle Talon TSi
    fwd · automatic · 2G DSM

    Street Build 2K  3

    1995 Eagle Talon TSi
    fwd · automatic · 2G DSM
  2. ec17pse

    ec17pse Freelancer

    Joined Nov 1, 2008
    London, UK, Europe
    The DP size and any silencers along the system will create pressure / slow the exhaust gases down. What size is yours and whats in your system?

    From what i read the twin scroll seem a little worse off for peak then they do for early delivery. (Im currently looking in a super 40) so i have read many threads on google and all suggest for a non twin scroll setup for max power but you loose low end which is ok for me but not everyone is ok with that.

    I have only breifly looked at your other holset thread but maybe i should look more as you talk about turbine housings so that may hekp me see what your currently running but it wont tell me your dp size etc. I dont think it will anyway unless you profile does

    Road Race Build 11K  11  57

    1997 Mitsubishi Eclipse GST
    175 whp · 180.1 lb/ft · 2G DSM
  3. biglady112

    biglady112 Proven Member

    Joined May 20, 2004
    Commerce City, Colorado
    Your transmission and baby cams are why your curve looks the way it does. You got the results you should expect.

    you think you have back pressure problems, install a sensor, log it and report back with factual information. Not someone’s guess.

    I am a big advocate for using back pressure data and have extensive knowledge on how it acts and when it is a problem. We would all be guessing without true data.

    put a real cam in it and you can watch the back of that curve take a nicer shape. Not a junk, baby regrind. Your intercooler is terrible and is not helping either and is costing you horsepower. And your small intake plenum as you can imagine is not helping matter either.

    you have other things to blame before the turbo. Camshafts mostly.
    Last edited: Oct 1, 2020
    Mello and ErikTande like this.
  4. RWD4G63

    RWD4G63 Proven Member

    Joined Dec 7, 2011
    Paw Paw, Michigan
    This. 524whp is a very respectable number from an HX35, and you are close to maxing that turbo out. Bigger cams and intercooler and you'll probably see 550+whp with better top end, and around that is the limit of that turbocharger.

    Road Race Build 359  3

    1997 Eagle Talon TSi AWD
    awd · manual · 2G DSM
  5. Sp1kE

    Sp1kE Proven Member

    Joined Dec 24, 2005
    stratford, ON, Canada
    I second this. I was having issues with my compounds, and everyone started screaming back pressure. A cheap sensor and some copper line goes a long way.
    In the end, the datalog clearly showed there was no backpressure issues. The log made about 7 people shut their yaps.
  6. ATF 2GTalon

    ATF 2GTalon Proven Member

    Joined Oct 28, 2002
    NYC, New York
    I've see many of your posts here and ecmlink forums and I don't think people give you enough credit for your knowledge and what you have done on your DSM before.

    What would you recommend for cams for HX35/HX40 sized turbos?

    And can you explain more about the transmission holding him back? Are you referring to slipping being the problem? And what mods would you recommend for auto people?

    Street Build 728  1

    1995 Eagle Talon TSi
    13.7 @ 105 · 2G DSM
  7. biglady112

    biglady112 Proven Member

    Joined May 20, 2004
    Commerce City, Colorado
    The biggest name brand cam you can get. My go to cams are GSC S3’s. They have fixed every car I have ever installed them in. I took a 2g this spring with this exact looking curve and made it stand all the way up out the back moving from kelford 272’s to the S3’s. And this was at 750hp and nothing else was changed mechanically.

    every car with an auto I have tuned has fallen off out the back. Wether it is at 6,000 or 9,000rpm. The converter just loses efficiency at some point and robs it making the car always seem less powerful on the Dyno. Obviously when on the street or track it proves to be quicker.

    precision spragless converter, full line pressure and another way to control the tranny besides the shit TCU.

    After 21 years I have seen and done it all from 150hp-1000hp. I don’t need the credit, nor do I seek it out. When I see bullshit, I call it out. Our air pump is no different than the next guys. Regardless of shape or size. Internal combustion engines really are that simple.

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