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One Borg Warner or the other one for M30B35?

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    One Borg Warner or the other one for M30B35?

    Hey dudes,

    I've got pretty much everything purchased to go FI on my M30 swap, except for an actual turbocharger. Goals are a modest ~7-10psi as early in the power band as I can get it. I live in an area with lots of hills and short twisty roads so I'm less interested in top end and more interested in quick response.

    As I had already decided on a Borg Warner unit, I used their matchbot tool and found two fairly good compressor map matches, one in the 200 series and one in the 300 series:

    I've been agonizing back and forth for literally days and I need to just pull the trigger on one or the other. Due to their current sale status and a coupon I have, they're basically identical in price from THMotorsports.

    The red dots on the maps below are my RPM/boost targets. Who's got votes either way?

    S200SX ~ $675 shipped:
    57.15mm / 76.2mm Compressor
    61.43mm / 69.56mm Turbine
    0.88 A/R Divided T4 housing


    S300SX ~ $700 Shipped:
    61.44mm / 83.47mm Compressor
    73.37mm / 79.76mm Turbine
    0.88 A/R Undivided T4 Housing
    Last edited by keyland; 07-15-2017, 07:05 PM. Reason: typo/details


    #2
    Looking at the differences between the two, I would say the S-200 flows slightly less and that makes sense to me as it has a smaller wheel size on both compressor and turbine. Also 79 lb/min vs 68 lb/min. This is strictly looking at maximum flow potential. Obviously you will not be making the maximum flow of either turbo (north of 500 hp) on 7 psi.

    From my experience, having turbo lag is not very fun because it makes the car feel lethargic when pushing the pedal down in the passing lane and this is the result from too large of a turbo. People seem to have this fascination with maximum power numbers when really 'area under the curve' is what matters for driveability.

    I would go with the S-200X and if you decide you want more power later there is plenty of room to grow by upping the boost( moving your points up and right due to higher pressure ratio on the vertical axis) but you won't be sacrificing low end like you would with the S-300.

    Look at point 2 on your maps, this I am assuming is about 2500 rpm. On the S-200 you are already at 72% turbo efficiency vs the S-300 you are a hair above 68% efficiency. That is going to be the main difference between the turbos and where the S-200 will outperform the S-300. Also, looking at point 6 which should be 6500 rpm or close to your redline, you won't usually be revved up to this point and the S-200 is starting to lose efficiency while the S-300 is in one of the second highest efficiencies on the map. You wouldn't want the turbo to start being its most efficiency when you you are getting ready to shift, you would want the turbo to be the most efficient somewhere in the middle where you can capitalize on the efficency and match that with the powerband of the engine.
    318iS Track Rat :nice: www.drive4corners.com
    '86 325iX 3.1 Stroker Turbo '86 S38B36 325

    No one makes this car anymore. The government won't allow them, normal people won't buy them. So it's up to us: the freaks, the weirdos, the informed. To buy them, to appreciate them, and most importantly, to drive them.

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      #3
      Thanks for the detailed analysis :)

      That's pretty much the exact observations/conclusions I came to as well. You can spend days and days looking at charts but sometimes you just need someone to agree/disagree.

      Point #2 on the graph was actually 3000RPM with #6 being 7000RPM but I just rescaled everything to make 2 = 2500 and 6 = 6500, and it actually fits even better into the higher efficiency islands on the S200.

      This definitely adds a little weight to my 'gut feeling' choice :D

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        #4
        Go with the s360. I don't know how a m30 flows compared to the m5x motors but I ran a s360 on my m52 and it got full boost at 3500ish and had power all the way to red line. I would think since the m30 is a 3.5 it would spool it even faster and still Have good top end.


        Sent from my iPhone using Tapatalk

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          #5
          Originally posted by grinchxvx View Post
          Go with the s360. I don't know how a m30 flows compared to the m5x motors but I ran a s360 on my m52 and it got full boost at 3500ish and had power all the way to red line. I would think since the m30 is a 3.5 it would spool it even faster and still Have good top end.


          Sent from my iPhone using Tapatalk
          M50 engines have compression over 10:1 and 4 valves per cylinder vs the m30b35 which is 9:1 and 2 valves per cylinder. The m30 also has beefy pistons and rods which spin up slower than the lighter rotating assembly of the m50 engines.

          Here is a datalog of my stroker m20 starting in 5th gear from about 1500 rpm to 5700 rpm. Yellow line shows boost pressure, the hump is wastegate opening with some boost creep. Gold line is rpm. Full boost under 3000 rpm is nice.

          318iS Track Rat :nice: www.drive4corners.com
          '86 325iX 3.1 Stroker Turbo '86 S38B36 325

          No one makes this car anymore. The government won't allow them, normal people won't buy them. So it's up to us: the freaks, the weirdos, the informed. To buy them, to appreciate them, and most importantly, to drive them.

          Comment


            #6
            Originally posted by downforce22 View Post
            M50 engines have compression over 10:1 and 4 valves per cylinder vs the m30b35 which is 9:1 and 2 valves per cylinder. The m30 also has beefy pistons and rods which spin up slower than the lighter rotating assembly of the m50 engines.



            Here is a datalog of my stroker m20 starting in 5th gear from about 1500 rpm to 5700 rpm. Yellow line shows boost pressure, the hump is wastegate opening with some boost creep. Gold line is rpm. Full boost under 3000 rpm is nice.





            I didn't know the m30 was such low compression, makes sense as to why they like boost so much.


            Sent from my iPhone using Tapatalk

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              #7
              After sleeping on it one more night, I've pulled the trigger on the 57mm S200-SX (aka S257SX).

              It seems like the most responsive option to meet my goal. Worst case, I just pass it on to an M20/M50 owner and get the S362 later. They use pretty much identical turbine housings and the discharge flange is totally identical so it wouldn't be too hard to change if I'm really unhappy.

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                #8
                For your goals you'll be happy, i ran a s256sx for 2 years and i really liked it on my m20. Now i have a s363sxe and it has a decent bit more lag and a higher threshold but still fun.

                Sent from my SAMSUNG-SM-G891A using Tapatalk
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                IX being restored here

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