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Thread: Questions about porting intake manifold

  1. #1
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    Default Questions about porting intake manifold

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    Factory TB/intake manifold is 60mm for a 4G69. The Eclipse GT 6G75 TB i have fitted to it is 65mm.

    I started to open this spare intake manifold up a bit (slowly taking my time) and im not sure if it is a good idea to open it all the way straight through to 65mm. 65mm happens to match the size of the gasket for reference.

    I know ill be restricted to the smallest section if i stop short around 62mm and bevel the eges to 65mm id assume that is still better than having the step that is there.

    My main concern is that im not sure it is safe to take as much material out of the throat? past the flange as I had initally planned due to how little material might be left.
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    So I got the opening to a full 65mm and the smallest cross section is now 63mm instead of 62mm, and it is all beveled when it shrinks down no harsh steps.

    This portion that the pick is pointing at is the part i'm unsure about removing more material from. I don't know how thin this can safely be cut before it is going to be a problem. It seems I have about 2-3mm of material left here as it stands right now.
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    The 2mm in diameter difference will likely have zero perceptible impact. Contrary to popular mis-information, one location with a smaller ID does not equate to the rest of the length having the same smaller diameter. It simply acts as a minor pressure drop/flow impediment, considerably less significant than the entire section having a reduced ID. The biggest improvement associated with the larger diameter is reduced losses across the throttle plate.

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    So in theory then i dont need to go any further... Having beveled out the stepped transition between the TB and IM is about as much benefit as ill see then, just finish cleaning it up and slap it back together?

    I saw no noticable difference from having moved from a 60mm to 65mm TB amd had always assumed the transition between the TB and IM was the problem. I also figured if it wasnt already 25% under driven with a light weight crank pulley that i might have also had a chance of noticing any kind of change when i origionally did the swap.
    Last edited by Izerous; June 23rd, 2018 at 06:34 PM.
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