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    Smaller turbos

    Does anyone have any recommendations and experience of smaller turbos for the M20B25?

    I want to build a flexible engine that will spool up very quickly (under 3000rpm). The roads are quite tight and twisty where I live in the UK. A responsive engine is a must so I don't get left behind exiting bends.

    Any suggestions would be great. I am happy for either internal or external wastegate.

    #2
    I'd also like to hear some first hand opinions, I have a .60/.63 turbo and its pretty nice but I get what you're looking for. I also have a Garrett Airesearch .42/.48 T3 that I want to try but need to rebuild first. I remember reading someone really liked that Garrett turbo but supposedly drops off past 6k.

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      #3
      My father used to own a Ford sierra Cosworth many years ago. I believe they used the Garett T3 .42a/r in those which were 227bhp and could easily handle 270bhp. I was thinking it would be just a little on the small side the 2.5 M20. I have been looking at the K24 off the Audi S2.

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        #4


        "in the videos we are running 8psi, from a small 42/48 turbo from a volvo 740. "

        looks fairly quick

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          #5


          here's their build

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            #6
            That's a really good read. Looks like it goes well!

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              #7
              Yea I would assume for a lower, sub 15 psi, it would work really well. I haven't seen any maps but just on their post that I saw on e30 tech they say it was in boost from 2000 rpms to 6000rpms (iirc) which is 99.99% of all the driving you do anyway. Which leads me to want to rebuild that garrett and give it a try.

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                #8
                But I can't imagine such a small turbo building significant boost, and probably chokes out in upper rpms. This is not first hand though.
                Considering how cheap K04 and the garrett airesearch is I'd say give them a shot but try and get a t3 flange manifold in case it doesn't work out the way you want you can put a bigger turbo on.

                I use an internal wastegate, has been working well for me. 8psi spring that I tightened to 10psi.

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                  #9
                  Hey guys, would a Garrett TB2514 from a 325tds work out for the M42? :)
                  I really want the early boost, and not that much of it, but will it be ok on the higher RPM's?
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                    #10
                    If the Sierra XR4I came with the same 60 trim T3 as the US market XR4TI, the turbo off of one is pretty much exactly what you're looking for. With a .63AR exhaust housing you'll definitely see boost before 3,000rpm on an M20. They're available used for very little money here. TD04HL-16T turbos off of Volvo 850s and others like them are another option, but the TD04s off of 740/940s are very restrictive on the turbine side, I don't recommend them for an M20, which is not only bigger than a B230ET but flows better.
                    Last edited by varg; 03-28-2016, 01:29 PM.

                    IG @turbovarg
                    '91 318is, M20 turbo
                    [CoTM: 4-18]
                    '94 525iT slicktop, M50B30 + S362SX-E, 600WHP DD or bust
                    '93 RX-7 FD3S

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                      #11
                      I used a TD04L off a 2.0 WRX years ago on the M20B23. It was making 6psi by 2000rpm and made 140RWKW at 7psi. Not huge numbers at all but it had TQ everywhere and as a street car it was a blast to drive around in. Bear in mind that this thing had a tiny turbine and really corked up the motor, you're NEVER going to get any impressive numbers out of something like this, but as a responsive street car it was great and won many traffic lights grand prix's!
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