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How big of a TB do you need....

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  • How big of a TB do you need....

    I took the measurement of the lower IM runners: 38mm
    Multiplied by 6 to get: 10.548 sq in. of area total for all 6 runners.

    Now say you build an upper manifold with plenty of volume, but wanted to find a single Throttle Body to match the lower plenums 10.548 sq. in. of area.

    Stock 50mm = 3.043 sq in. (wow, only 1/3 of the area :roll: )
    240sx 60mm = 4.383 sq in.
    65mm = 5.143 sq in.
    75mm = 6.848 sq in.
    85mm = 8.795 sq in.
    95mm = 10.987 sq in. (winner?)


    A 95mm TB typically is good for over 1200hp, so there's really no reason to port the lower manifold.
    1987 300ZX Turbo - http://www.z31performance.com/forum/vie ... php?t=3114
    2001 Tiburon Turbo 60-1 270whp/268tq

    No cupholders? Where am I gonna put my beer????


  • #2
    except that you never use all the runners at the same time... the higher the rpm the closer to the theoretical threshold you get but still about half when dealing with airflow

    you can look at it as reducing obstruction, and doubling the area will be more than adequate for even 10k rpm

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    • #3
      i have been thinking about this as i am building a one-off plenum soon , i was thinking maybe a q45 TB would maybe use the same type of TPS so that would be a good choice for me who wants to stay with the stock tps , but then again i dont know it will work or not im just assuming ..

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      • #4
        you can still make 700whp with a 60mm TB, but that doesn't mean it's a restriction. It's nice to have a big TB, as you know it will not be a restrictoin

        But with a large TB, drivability is sacrificed. Just cracking the throttle a hair will flow a ton of air and the car will be hard to controll at low throttle and low RPM.

        For a street car, I wouldn't go with more than a 75mm.
        86 hardtop shell, 93 SC300 engine, 95 soarer bellhousing, 91 supra transmission, 95 Q45 differential hubs and driver's side axle, 1992 300ZX turbo driver side axle and calipers, 2004 350Z Rotors, 87 300ZX front end/hood, 1999 Viper radiator, 1992 Mustang throttle body. Lots of glue and tape to keep it all together.

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        • #5
          StreetFighter wrote: you can still make 700whp with a 60mm TB, but that doesn't mean it's a restriction. It's nice to have a big TB, as you know it will not be a restrictoin

          But with a large TB, drivability is sacrificed. Just cracking the throttle a hair will flow a ton of air and the car will be hard to controll at low throttle and low RPM.

          For a street car, I wouldn't go with more than a 75mm.
          Generally one who runs a Q45 throttle body that has an 80mm venturi (yes its 80 not 90mm, I checked) has a pretty large turbo and cracking the throttle open a little bit does NOT make the car undriveable, Not even close. Now if you had maybe a stock T3 and a 80mm throttle body, that MAY be different, but who in there right mind would do that?

          2+2turbo. the q45 TB does use a similar TPS however the TPS mounts on the opposite side so the TPS off of a z or a 240sx is backwards and you have to cut and cross the red and green wires (I belive its the red and green, I would have look again to see which ones they are).
          85 Z31 6.0 LSX turbo 766whp/792wtq
          04 GTO, LS6, big cam, porting, N20... underway for summertime daily driver.

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          • #6
            SATAN wrote:
            2+2turbo. the q45 TB does use a similar TPS however the TPS mounts on the opposite side so the TPS off of a z or a 240sx is backwards and you have to cut and cross the red and green wires (I belive its the red and green, I would have look again to see which ones they are).
            Or you could use a Pathfinder TPS. It's backwards compared to those on a Z31.
            [strike:ff0tp92h]1984 300ZXT[/strike:ff0tp92h]
            [strike:ff0tp92h]1986 300ZX 2x2 NA2T[/strike:ff0tp92h]
            2000 Porsche Boxster
            2007 Toyota Yaris

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            • #7
              Run a 105mm TB and try to baby it around... It's a bitch, trust me. an 80mm TB is still streetable, but the larger throttle will flow a lot more air at part throttle.

              There is a big difference between an 80mm and a 105mm. I drove our racecar (105mm TB, 88mm T6 turbo) into a bay to put it on a lift, and it was a bitch. It surged under very slight throttle, making the car lurch.
              86 hardtop shell, 93 SC300 engine, 95 soarer bellhousing, 91 supra transmission, 95 Q45 differential hubs and driver's side axle, 1992 300ZX turbo driver side axle and calipers, 2004 350Z Rotors, 87 300ZX front end/hood, 1999 Viper radiator, 1992 Mustang throttle body. Lots of glue and tape to keep it all together.

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