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Thread: 2.5 one piece intake manifold modification

  1. #1
    Supporting Member II Turbo Mopar Contributor
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    2.5 one piece intake manifold modification

    When modifying a one piece intake for a 2.5l turbo what effect would shortening the runners have on the power band.

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    Supporting Member II Turbo Mopar Contributor tryingbe's Avatar
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    Re: 2.5 one piece intake manifold modification

    Nothing much if the cylinder head can't take the flow at higher RPM.

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    Re: 2.5 one piece intake manifold modification

    Will have a FWD motion enforcer stage 2 head assembly

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    Supporting Member II Turbo Mopar Contributor tryingbe's Avatar
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    Re: 2.5 one piece intake manifold modification

    Are you planning to cut the intake manifold in half then modify it?

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    Re: 2.5 one piece intake manifold modification

    possibly

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    Supporting Member II Turbo Mopar Contributor ajakeski's Avatar
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    Re: 2.5 one piece intake manifold modification

    Unless you just really want to spend a bunch of time on a one piece, you're better off with a modified two piece or a custom intake.

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    Supporting Member Turbo Mopar Contributor GLHS60's Avatar
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    Re: 2.5 one piece intake manifold modification

    Quote Originally Posted by Kevin_Hemenway View Post
    When modifying a one piece intake for a 2.5l turbo what effect would shortening the runners have on the power band.
    Raises the powerband considerably, no down side, retarding the cam also raises the powerband.

    There are a few good threads with pics if you can find them.

    Health issues prevent me providing links at this time, maybe someone else can.

    Boost Geek, Speed freak 500, Shadow Joey and others have had great success,all while using stock ported exhaust manifolds.

    Thanks
    Randy


    Randy Hicks
    86 GLHS60
    86 GLHS 373 : SOLD, but never forgotten
    89 Turbo Minivan
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    Re: 2.5 one piece intake manifold modification

    I was under the impression that shorting the runners would reduce low end torque. Which may be good for racing but not a DD. This is why some engines have the ability to effectively short the flow path during higher RPM using shutters or such devices.
    Regards,
    Miles

    DD '87 Sundance T1, 12PSI, SLH with rear disks
    '87 CSX #432

  9. #9
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    Re: 2.5 one piece intake manifold modification

    a 2.5 has so much torque to spare that if you do lose torque it's not such a bad thing as you then hook instead of spin. That being said when I went to a ported head, ported 2 piece lower and a big plenum intake which shortened the runners by however much you do by getting rid of the stock plenum (no I didn't use a lengel upper) I was scared from all the stories that I'd heard over the years that the car would be a dog down low. Hah, it didn't lose anything that I noticed down low at all and would pull 5th gear from idle all the way to as far as you could go before running out of road.

  10. #10
    Moderator Turbo Mopar Staff Force Fed Mopar's Avatar
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    Re: 2.5 one piece intake manifold modification

    Yeah on a 2.5, I wouldn't worry about low end at all, I'd do everything I could to make it breathe up top.
    Rob M.
    '89 Turbo GTC
    2.5 TIII swap is here!

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    Back to basics, then the mods go back on....

  11. #11
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    Re: 2.5 one piece intake manifold modification

    Quote Originally Posted by GLHNSLHT2 View Post
    a 2.5 has so much torque to spare that if you do lose torque it's not such a bad thing as you then hook instead of spin. That being said when I went to a ported head, ported 2 piece lower and a big plenum intake which shortened the runners by however much you do by getting rid of the stock plenum (no I didn't use a lengel upper) I was scared from all the stories that I'd heard over the years that the car would be a dog down low. Hah, it didn't lose anything that I noticed down low at all and would pull 5th gear from idle all the way to as far as you could go before running out of road.
    Thanks for the comment. I will see what my 2.5 CSX is like once I get t on the road. Ported head with +1 etc
    Regards,
    Miles

    DD '87 Sundance T1, 12PSI, SLH with rear disks
    '87 CSX #432

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    Re: 2.5 one piece intake manifold modification

    From what I understood from talking to V8 muscle guys they were always trying to get long runners for top end ie. high rise intakes so i was concerned that shortening the runners in the one piece would have a negative effect on the top end speed/power band

  13. #13
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    Re: 2.5 one piece intake manifold modification

    completely backwards.. short straight runners for top end. long runners for low end.

    the point of high rise intakes are to create a straighter path for the air directly to the intake valve. the intake runner length stays the same or shorter.

  14. #14

    Re: 2.5 one piece intake manifold modification

    Kevin, read thru this thread. should answer all your intake questions.http://www.turbo-mopar.com/forums/sh...Warren+Stramer
    Worlds fastest 8 Valve 6.3sec., 119.70 1/8, Best MPH 145.5, Best 1/4 ET 9.78 sec.,144.26mph. 8 valve NO NITROUS!!

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    Re: 2.5 one piece intake manifold modification

    Quote Originally Posted by GLHNSLHT2 View Post
    a 2.5 has so much torque to spare that if you do lose torque it's not such a bad thing as you then hook instead of spin. That being said when I went to a ported head, ported 2 piece lower and a big plenum intake which shortened the runners by however much you do by getting rid of the stock plenum (no I didn't use a lengel upper) I was scared from all the stories that I'd heard over the years that the car would be a dog down low. Hah, it didn't lose anything that I noticed down low at all and would pull 5th gear from idle all the way to as far as you could go before running out of road.
    Even on my 2.2. Big upper plenum and throttle body improved response more than anything.

  16. #16
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    Re: 2.5 one piece intake manifold modification

    On my modified 1 piece, I noticed lag increased by about 400 rpms, but it was totally worth the top end increase. I cut off a 1 piece just above the rail mounting holes and built a box plenum with a 3.3l elbow and 58mm tb. HOWEVER I also changed the manifold from a stock log to tbi at the same time.

  17. #17
    Supporting Member Turbo Mopar Contributor mopar-tech's Avatar
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    Re: 2.5 one piece intake manifold modification

    Quote Originally Posted by masterjr33 View Post
    completely backwards.. short straight runners for top end. long runners for low end.

    the point of high rise intakes are to create a straighter path for the air directly to the intake valve. the intake runner length stays the same or shorter.
    It is a complex topic- Runner length, diameter, runner volume and plenum volume all play important rolls. The tunnel ram on my GTX has far longer runners than the TM7 I run time to time, power wise the tunnel ram lays waste to the TM7 in both torque and hp. This isn't always the case with tunnel rams, the particular unit just happens to have the proper design for the displacement, cam and head selection.

    The short answer to your question is on the one piece intake shortening the runners will be of some benefit for the 2.5 engine moving the powerband up a notch as long as you have other supporting pieces. Intercooler and turbo will act as throttling devices if not properly sized.

    Gary


    It is time, buckle up.

  18. #18
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    Re: 2.5 one piece intake manifold modification

    Thank you all for the input the thread warren linked was some very good reading. I have decided to leave the runners for now and cut the elbow off remove the top of the intake and weld on a 2.5" tube +90 across the whole thing for now as well as the larger tb.

  19. #19
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    Re: 2.5 one piece intake manifold modification

    Thanks to all for the input i have completed my intake manifold alterations.
    http://photos.app.goo.gl/doihC4G1Bg79w7sF6

  20. #20
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    Re: 2.5 one piece intake manifold modification

    Cool work! Factory rail and mounting holes, factory knock sensor and vacuum port. You may regret not adding an intake temp sensor bung, but it looks good. Huge improvements in the elbow. What did you do inside before welding it up?

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