Matt’s Theory on Rotated vs. Stock location turbos

Discussion in 'Modifications & DIY how-to' started by slowwrx, Oct 18, 2006.

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  1. slowwrx

    slowwrx Supporting Member

    Matt’s Theory on Rotated vs. Stock location turbos

    I thought that I would post this up in its own thread as it would be easier to find later.


    Here are a few things you have to consider about stock location vs. rotated.

    1. Wastegate Style
    A. Internal
    Obviously with an internal gate you are limited to what size opening you can have. They tend to be harder to control and don’t work well on large turbos. Internal gates are no usually found on rotated kits because most people that are going rotated are also going to a large turbo that internal gates are not found on.

    B. External
    External gates are larger and easier to control than an internal gate. They are really you’re only option when approaching the 500whp range.

    2. Exhaust Housings
    This could get very long I will Try and keep it simple, I will get more detailed when I explain my personal setup at the bottom.

    A. Stock mount
    With a stock mount turbo the exhaust housing tends to get squished so that it fits into place nicely on the back side of the motor. When you squish the exhaust housing you limit flow and you also limit which turbine wheels you can use in it.

    B. Rotated mount
    Rotated mounts allow you to use a standard turbo so now you are not limiting the size or shape of the exhaust housing, large twin scroll turbos are now an option that you would never have with a stock mount.
    1. Garrett
    Garrett limits you to .63 and .82 exhaust housings

    2. Precision
    Precision lets you use a .48, .63, and .82

    3. Compressor Housings
    I will also go more in-depth with this subject when I get into my personal setup.

    A. Stock Mount
    Just like the exhaust housings these also suffer in the stock locations, the housing gets squished and you can’t fit the really good compressor wheels in there. If you are staying 20G and smaller then this isn’t a problem.

    B. Rotated Mount
    No problem fitting big housings, so in turn there is a problem fitting a big compressor wheel.

    1. Garrett
    Garrett uses anti surge housings on their GT series turbos

    2. Precision(aftermarket)
    Precision you can order the turbo with or without the anti surge housing. You can also order different size compressor covers.
    (More on this in my setup)

    4. Turbo Size
    Again with a stock location turbo you are limited on size, with a rotated you are not.

    5. Inlet Size
    This is another place where you are limited by the stock location, you can only fit an inlet under the manifold that is so big, with the rotated mount you can go as big as you like.

    Stock location turbos
    The good thing about a stock location turbo is that it fits in the stock location, which means minimal fabrication work and a bolt on installation. Honestly if you’re not going bigger than a 20g or a Green then I can’t think of any reason to go rotated. Stock location turbos have no problem getting to the 400-450hp mark.

    Rotated Mount
    I like the rotated mount because it opens up a lot of options you can do anything from a TD04 size turbo to a 4788. You have now opened up the inlet so that the turbo can breathe; it doesn’t have to work as hard to make the same power so it should last longer.

    My personal setup

    My setup consists of the Perrin Up and Down pipe and the Perrin inlet (about to change to a MSPT). The turbo itself is the trick part of the setup because no one else is currently running it that I know of. It is a Precision GT30R (3076) with a T04S cover (no anti surge) and a .48 hot side. I hit full boost at 3600 rpms and the car pulls strong all the way to redline. If you are building a street car or a road race\autocross car then I would highly recommend this setup. We should have it on the dyno this week to confirm the numbers but I suspect that it’s making very close to 400hp on pump gas and I can assure you that Scott was very conservative with the tune. The car has run 1 hours sessions at Roebling Road and CMP and has never even had the slightest hint of knock. I can’t even begin to explain how much fun it is to drive.

    (If you have questions fire away)

    Oh one last thing the anti surge housings on the gt30r are a huge waste of time and you’re spool will suffer, mine has never surged even with the small hot side on it.
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