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1G What hp to ditch the OEM Intake Manifold?

Posted by burkgonzo, Jul 7, 2018

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  1. burkgonzo

    burkgonzo Proven Member

    773
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    Joined Oct 27, 2005
    Wichita Falls, Texas
    Currently I'm running an extrude honed stocker and what point would I gain switching over to a Magnus or some other SMIM?
     

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  2. bastarddsm

    bastarddsm Supporting Vendor

    4,190
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    Joined Aug 26, 2003
    Mendota, Illinois
    When you dontd care about power under 6000, and need peak power at 10k.
     
    My DSM:
    1991 Eagle Talon N/T

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  3. donniekak

    donniekak DSM Wiseman

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    Joined Mar 23, 2008
    Surprise, Arizona
    It’s not about power it’s about rpm and powerband. The stock intake wants to make peak power at 6500ish rpms. If your setup spools after 4500 rpms you’ll benefit from a longer powerband with an aftermarket intake.

    My forester and kelford 272’s made peak power at 8800 rpms. This was on a late spooling turbo as well.
     
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  4. donniekak

    donniekak DSM Wiseman

    4,427
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    Surprise, Arizona
    With a forrester intake, comp 272’s, and a 3076 in a .63 housing my car makes power from before 4500rpms out to 8500.
     
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    1991 Eagle Talon TSi AWD

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  5. bastarddsm

    bastarddsm Supporting Vendor

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    Mendota, Illinois
    I did some extensive dyno testing on this, and even on a 64mm turbo the short runner intakes are not the choice for me. Im trying to get my car to leave off a 5k 2step, shift 1-2 at 9500, and still be in the power. at 5k an evo3 intake on a 6 bolt head is worth over 75hp compared to a short runner intake, and it doesn't fall off. Stock is worth more, but does fall off more after 7k.

    Anyway my thoughts are a 64mm and tx272s are notn enough to use a short runner smim.
     
    My DSM:
    1991 Eagle Talon N/T

    Showcar Build

    9.805 @ 144.00 MPH
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  6. Galant665

    Galant665 Proven Member

    34
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    Joined Oct 1, 2004
    Las Vegas, Nevada
    I have a Forrester and haven't tested it yet. Stock intake on an auto setup making 521 tq at 3200 now. Betting the SMIM loses a considerable amount of low and mid range. On old 20 yr Crower 272s its still making power at 7000 but started to fall. I like the total power and torque curve it has now. Can shift it 7000 all three gears and its never in a weak area.
     
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  7. donniekak

    donniekak DSM Wiseman

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    I did a ton of testing 2 years ago and found a small exhaust housing, smallish cams, and short runner intake to give me the best powerband. It knocked 100hp off my peak hp at the same boost, but brought power on 1,000’s of rpms sooner in the lower gears. I ended up holding power flat from 7,000-9,000+ rpms, with peak boost at 5,200 rpms in 3rd.

    This was a fp 3586htz.

    The forrester seems to work better than most intakes at preserving midrange, and the top end is limitless.


    With my current setup I can make 20 psi before 4,000 rpms.


    I specifically set out to come up with a way to make the most power possible with low torque to keep the trans ok. I made 601 at 24psi and 400lb/ft with the 3586.
     
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  8. dragonov_elite

    dragonov_elite Proven Member

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    Joined Jul 14, 2005
    La Crosse, Wisconsin
    Are the Forrester intakes still being made or are they a rare find now days? considering one for my build and have read good things about them.
     
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  9. donniekak

    donniekak DSM Wiseman

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    Good luck finding one. When they pop up they usually go quick. They haven’t been made for a long time. I wouldn’t recommend one for most people that have a turbo that spools at 4500 rpms or under. With a mid frame turbo it really takes an all out build to take advantage of the forrester.
     
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  10. diambo4life

    diambo4life Proven Member

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    Edmond, Oklahoma
    With your current setup, I think stock intake is best. You lose substantial low and midrange with a SMIM as mentioned above.
     
    My DSM:
    1990 Mitsubishi Eclipse GSX

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    710 whp   501 lb/ft
    1991 Eagle Talon TSi AWD (sold)

    10.56 @ 136.45 MPH
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  11. ist dwa

    ist dwa Proven Member

    174
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    Joined Nov 5, 2009
    Centerville, Ohio
    IMO there is no reason to change the stock intake manifold unless you are trying to make over 1000hp. Everybody does it, doesn't mean it is right. The real limitation of the stock intake is not the plenum or runners, it's the inlet size. Good rule of thumb is tbody should match compressor ID. SO stock is 2.5" that is a 35r turbo which are capable of around 800hp in the right hands.

    You next turbo up is a 37r which is 67mm I believe...again still close to that 65mm and those babies are good for around 900whp.....you see where I am going with this.

    If you are interested in a Forrester, I saw Kyle Cymbas had one for sale about 2 weeks ago for $500.

    OP, the fact you have an extrude honed intake is super bad ass, that manifold should perform very well, I would never get rid of that thing. It is very expensive to have that process done. I would look at somehow just getting a larger flange welded on it for a larger 70mm t-body if your plans are to go large HP.

    I really learned the myth of the stock intake when I was at the SO one year at the dyno day, STM had some EVO monster that laid down 9XX WHP down on Buschur's dyno on that puny stock intake manifold. Light bulb went off right there....that part isn't that important.
     

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