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Thread: High compression, low boost?

  1. #1
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    High compression, low boost?

    Been reading just about every build thread on here and hoping that around the end of the summer I'll finally be able to finally get started on my own build. While I'll have another vehicle to drive during the build, ultimately this will go back to being my daily driver so I have more modest goals than a lot of the cars here. Mainly looking for 350-400whp on E85 and to keep AC. Just looking for some advice on what parts I'm currently looking at...

    120K M50B25 (compression within 5 psi on all cylinders, runs great)
    S50 cams
    3 inch turbo back
    Cut ring gasket
    ARP head studs
    SPA bottom mount manifold
    BW S257SXE
    eBay intercooler (probably going to get an overkill intercooler for when I want more power down the road)
    RK Tunes or MS PNP

    I'm wanting to stay on stock compression to help spool and make torque on the low end. I know for higher boost that basically will require E85, which I have available. However, for roadtrips and daily driving, is stock compression + 91 octane + wastegate pressure (6-8 psi) going to be safe for the engine?


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    '93 325is: ZF swap, Borla Type X muffler, cat delete, X Pipe, Tune, Powerflex bushings (subframe, diff, RTAB, LCAB), Apex ARC8's, Raceland Ultimos, Corbeau seat, Renown steering wheel, M3 front and rear bumpers, BMW motorsports moulding, Euro tails, Depo headlights (soon to be retrofitted)




  2. #2
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    The issue with your plan is the OEM rods. You need to reduce the low end torque and move the curve to the right so you dont squish them.

    The recipe you proposed is usually to increase low end torque and response which will cause problems. See Rajicase's thread.

    At the low power goals it might not be a huge issue, but its doubtful he would stay at that level for long
    -Nick
    91 E30 M42 on VEMS

    Turbo Camshaft Thread

  3. #3
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    The rod on the right is an s52 like raji and many others have pretzeled up. The rod on the left is an m50 rod. You can't hurt an m50 rod at 400 whp provided the tune is not jacked. 8 pounds on pump sounds feasible to me.



    86 325es, 2.8L m50, S476sxe, ProEFI 128 ecu, e85, solid rear axle, TH400 trans, 28x10.5w slicks, zip ties, popsicle sticks, tape
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  4. #4
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    I maxed a s256sx out on my stock s52 rods. It made 465whp/418wtq. As soon as I put the 366sxe in on e85 at 21psi it bent several rods after just a few quick pulls.

    I think 6-8lbs on 91 octane is probably about as high as you'd want to go on stock compression.

    I would strongly suggest lowering compression if you ever plan on running 91 octane.....

  5. #5
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    Like I said, really wanting to keep stock compression just for off boost response and to minimize lag. Running on pump would be for DD/roadtrip duty, anything that involves me beating on the car is realistically going to involve E85 and high boost

    Sent from my SM-G920V using Tapatalk
    '93 325is: ZF swap, Borla Type X muffler, cat delete, X Pipe, Tune, Powerflex bushings (subframe, diff, RTAB, LCAB), Apex ARC8's, Raceland Ultimos, Corbeau seat, Renown steering wheel, M3 front and rear bumpers, BMW motorsports moulding, Euro tails, Depo headlights (soon to be retrofitted)




  6. #6
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    You're really going to want to get aftermarket internals if you want to go that route

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  7. #7
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    Quote Originally Posted by tyr283 View Post
    Like I said, really wanting to keep stock compression just for off boost response and to minimize lag. Running on pump would be for DD/roadtrip duty, anything that involves me beating on the car is realistically going to involve E85 and high boost

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    You should drive a properly set up properly tuned responsive turbo lowered compression car. Response is great. Off boost response is great. Lag is not an issue. It's the way to go.

  8. #8
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    So you guys think I'll be better off with copper spacer then?

    Sent from my SM-G920V using Tapatalk
    '93 325is: ZF swap, Borla Type X muffler, cat delete, X Pipe, Tune, Powerflex bushings (subframe, diff, RTAB, LCAB), Apex ARC8's, Raceland Ultimos, Corbeau seat, Renown steering wheel, M3 front and rear bumpers, BMW motorsports moulding, Euro tails, Depo headlights (soon to be retrofitted)




  9. #9
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    Definitely. But consider buying a more responsive turbo even if it costs more. Butters has a customer with a journal bearing 0.63 PT6262 that seems happy, though I have not driven the car. With your 2.5L you will want a responsive turbo and to be able to run higher boost. Spa T3 manifold and maybe PT6262. Maybe an even smaller turbo but not a diesel truck turbo like the BW even if you can get a small back housing for it.
    Last edited by pbonsalb; 06-26-2017 at 08:35 AM.

  10. #10
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    Quote Originally Posted by pbonsalb View Post
    Definitely. But consider buying a more responsive turbo even if it costs more. Butters has a customer with a journal bearing 0.63 PT6262 that seems happy, though I have not driven the car. With your 2.5L you will want a responsive turbo and to be able to run higher boost. Spa T3 manifold and maybe PT6262. Maybe an even smaller turbo but not a diesel truck turbo like the BW even if you can get a small back housing for it.
    I got ahold of an HX35W for about $200, it is very responsive and quick spooling too, my build is not finished yet but full boost is at about 4000rpm

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  11. #11
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    My decision for the BW was actually after riding in a Z3 with a S256 and an M52...I know the extra bit of displacement definitely helps but it made right at 400whp on 93 and spool was great. With the lighter wheels and the fact that it flows more to boot, I think that the S257 is a good option considering it spools damn near like a GT3076R (at least according to Rapidspool's testing) and BW turbos are renowned for being very close to indestructible

    Sent from my SM-G920V using Tapatalk
    '93 325is: ZF swap, Borla Type X muffler, cat delete, X Pipe, Tune, Powerflex bushings (subframe, diff, RTAB, LCAB), Apex ARC8's, Raceland Ultimos, Corbeau seat, Renown steering wheel, M3 front and rear bumpers, BMW motorsports moulding, Euro tails, Depo headlights (soon to be retrofitted)




  12. #12
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    The S256 that raji had was a dog in terms of spool. But he had a massive back housing -- maybe a 1.22?

  13. #13
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    Quote Originally Posted by pbonsalb View Post
    The S256 that raji had was a dog in terms of spool. But he had a massive back housing -- maybe a 1.22?
    Yeah he had the biggest back housing they come with because he was worried about choking it up top. When rapidspool tested it back to back on their Evo with a GT3076R it spooled a couple hundred rpm faster and made 40whp more I believe

    Sent from my SM-G920V using Tapatalk
    '93 325is: ZF swap, Borla Type X muffler, cat delete, X Pipe, Tune, Powerflex bushings (subframe, diff, RTAB, LCAB), Apex ARC8's, Raceland Ultimos, Corbeau seat, Renown steering wheel, M3 front and rear bumpers, BMW motorsports moulding, Euro tails, Depo headlights (soon to be retrofitted)




  14. #14
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    Quote Originally Posted by pbonsalb View Post
    The S256 that raji had was a dog in terms of spool. But he had a massive back housing -- maybe a 1.22?
    Yeah my 366sxe spools quicker lol.
    The 1.22 was not the crrect choice lol.

  15. #15
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    Quote Originally Posted by rajicase View Post
    Yeah my 366sxe spools quicker lol.
    The 1.22 was not the crrect choice lol.
    I'm glad we had you to test that for us since there aren't many BMW guys playing with BW turbos it seems

    Sent from my SM-G920V using Tapatalk
    '93 325is: ZF swap, Borla Type X muffler, cat delete, X Pipe, Tune, Powerflex bushings (subframe, diff, RTAB, LCAB), Apex ARC8's, Raceland Ultimos, Corbeau seat, Renown steering wheel, M3 front and rear bumpers, BMW motorsports moulding, Euro tails, Depo headlights (soon to be retrofitted)




  16. #16
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    Quote Originally Posted by tyr283 View Post
    Yeah he had the biggest back housing they come with because he was worried about choking it up top. When rapidspool tested it back to back on their Evo with a GT3076R it spooled a couple hundred rpm faster and made 40whp more I believe

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    Do you have a link to that testing?


    86 325es, 2.8L m50, S476sxe, ProEFI 128 ecu, e85, solid rear axle, TH400 trans, 28x10.5w slicks, zip ties, popsicle sticks, tape
    best time 9.06 @ 151.8 mph, best 60 foot 1.30

  17. #17
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    Quote Originally Posted by someguy2800 View Post
    Do you have a link to that testing?
    Idk why I said rapidspool, meant full race...this was back to back dyno they did with a twinscroll S256 and a GT3076R on an Evo 9 and then an overlay of a GTX3071 on a different car with the same setup. They had a thread about it somewhere on Evo forums but I have no idea how to find it again

    Sent from my SM-G920V using Tapatalk
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  18. #18
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    I plan to use the same turbo on my z3 eventually. I'd say just run a 0.90 gasket to drop compression a bit (IIRC that will give you 9.5:1) than run 8-10 psi on 91 and 16-20 on e85. Torque kills rods, but you don't have to worry as much with a smaller displacement m50. Franc proved a stock compression m50 with a cutring and studs can handle 700+whp/500wtq on stock internals on e85 with good tuning. You will max probably out that turbo on e85 before you bend a rod, provided you have good tuning.

  19. #19
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    For a 2.5L and 300-400 HP I'd be strongly looking at a 5858 or Garrett version 5857.
    Or you can have 2k rpm powerband with the a 62mm+ turbo. That's no fun in my opinion
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  20. #20
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    Quote Originally Posted by Butters Stoch View Post
    For a 2.5L and 300-400 HP I'd be strongly looking at a 5858 or Garrett version 5857.
    Or you can have 2k rpm powerband with the a 62mm+ turbo. That's no fun in my opinion
    62+mm? I was looking at a 57mm...and I do want to have some headroom on how much I can make down the road. I just want to start with a somewhat reliable and manageable power figure since even 350whp is double what it makes now

    I did look at the 5858 but it seems pretty comparable to a S257SXE at a much higher cost, unless I'm missing something

    Sent from my SM-G920V using Tapatalk
    '93 325is: ZF swap, Borla Type X muffler, cat delete, X Pipe, Tune, Powerflex bushings (subframe, diff, RTAB, LCAB), Apex ARC8's, Raceland Ultimos, Corbeau seat, Renown steering wheel, M3 front and rear bumpers, BMW motorsports moulding, Euro tails, Depo headlights (soon to be retrofitted)




  21. #21
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    Quote Originally Posted by tyr283 View Post
    62+mm? I was looking at a 57mm...and I do want to have some headroom on how much I can make down the road. I just want to start with a somewhat reliable and manageable power figure since even 350whp is double what it makes now

    I did look at the 5858 but it seems pretty comparable to a S257SXE at a much higher cost, unless I'm missing something

    Sent from my SM-G920V using Tapatalk
    That's more like a 5761 , with the turbine housing its what cost ? A JB precision 5858 or Garrett JB can be had for around $900. With the bigger turbine wheel of the s257 you will sacrifice spool on a 2.5L.
    1996 332IS
    Built 3.2
    CES/Steed TS Precision 6466, spraying a "$π!℅" load of meth.
    Technique Tuning 80# tune.
    1/4 mile 10.84 @ 136.72
    Your 1 and only stop for all your BMW performance needs
    WWW.CESMOTORSPORT.COM

  22. #22
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    Quote Originally Posted by Butters Stoch View Post
    That's more like a 5761 , with the turbine housing its what cost ? A JB precision 5858 or Garrett JB can be had for around $900. With the bigger turbine wheel of the s257 you will sacrifice spool on a 2.5L.
    When I checked T3 .82 AR 5858 with V band outlet was around $1200

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    '93 325is: ZF swap, Borla Type X muffler, cat delete, X Pipe, Tune, Powerflex bushings (subframe, diff, RTAB, LCAB), Apex ARC8's, Raceland Ultimos, Corbeau seat, Renown steering wheel, M3 front and rear bumpers, BMW motorsports moulding, Euro tails, Depo headlights (soon to be retrofitted)




  23. #23
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    Quote Originally Posted by tyr283 View Post
    When I checked T3 .82 AR 5858 with V band outlet was around $1200

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    Well, that seems high. I can get you one for $949.95 + shipping.
    1996 332IS
    Built 3.2
    CES/Steed TS Precision 6466, spraying a "$π!℅" load of meth.
    Technique Tuning 80# tune.
    1/4 mile 10.84 @ 136.72
    Your 1 and only stop for all your BMW performance needs
    WWW.CESMOTORSPORT.COM

  24. #24
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    Quote Originally Posted by Butters Stoch View Post
    Well, that seems high. I can get you one for $949.95 + shipping.
    That's better. I'll PM you when I'm ready to start ordering parts.

    Is there a simpler way to have multiple tunes on OBD1 besides switching ECU's?

    Sent from my SM-G920V using Tapatalk
    '93 325is: ZF swap, Borla Type X muffler, cat delete, X Pipe, Tune, Powerflex bushings (subframe, diff, RTAB, LCAB), Apex ARC8's, Raceland Ultimos, Corbeau seat, Renown steering wheel, M3 front and rear bumpers, BMW motorsports moulding, Euro tails, Depo headlights (soon to be retrofitted)




  25. #25
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    Same price for the Garrett GTW 5857 , or the GTW 6262 is a hair more. But too much for a street 2.5L
    1996 332IS
    Built 3.2
    CES/Steed TS Precision 6466, spraying a "$π!℅" load of meth.
    Technique Tuning 80# tune.
    1/4 mile 10.84 @ 136.72
    Your 1 and only stop for all your BMW performance needs
    WWW.CESMOTORSPORT.COM

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