2.5 RS Max boost PSI

Discussion in 'General Subaru Discussion' started by Bielke55, Oct 27, 2005.

  1. Bielke55
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    Bielke55 Well-Known Member

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    Does Anyone Know what the max PSI a 2.5 RS Motor can with stand before things get messy? i have a boosted 2.5RS, that i want to increase boost to 7 or 8 but im unsure of its limits. If anyone knows please let me know. Thanks

    -B
     
  2. hercules
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    hercules New Member

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    im like boosting 15 in my 2.0 RS...but im sure zola or Russ should know the answer to that....btw what kind of FMIC is that???
     
  3. WRX1
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    WRX1 _ Staff Member

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    What kind/ how big is your ic? Do you have a ic? What kinda of engine management do you have? Do you have a way to increase your fuel flow and decrease your timing?

    Russ
     
  4. AWDimprezaL
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    AWDimprezaL has more posts than you

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    ive heard 8-10 is pushing it, kelly has a boosted RS, phatsuby has a boosted 2.5 in his lgt.
     
  5. esperunit
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    esperunit Well-Known Member

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    8-10 is pushing it.

    That's not really the engine setup to have if you are the kind of person who wnats to tuen up the boost one day. Running 8+ psi will cause that engine to blow sooner or later. Some people swear they run 8 all the time, but nobody swears they run 10.
     
  6. Zola
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    Zola Well-Known Member

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    Totally depends on which turbo you have on there and your state of tune, there is no magic maximum boost pressure number.
     
  7. RallyNavvie
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    RallyNavvie Well-Known Member

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    Where the hell do all these RS turbos come from these days? Like they grow on trees, I swear...

    Anyway your "safe" number for stock internals AND decent engine management is 5psi. I guess I never understood why people would want to take the chance of blowing up their engine by going beyond that without putting more work into the engine when 5psi makes the high-CR n/a plant pretty damn quick. At least it felt a lot quicker than my GT does.

    You can push to 8-10psi on stock internals ONLY if you're running proper engine management. I had a Haltech E6K in mine, or there's the TEC-II or 3 (which I don't recommend because I don't think either had air temp correction maps), or the Link. Look under the engine management sticky thread at NASIOC, it has a comparison of several geared more toward aftermarket turbos.

    Once you start changing out internals you may as well just get an STi 2.5 block and build on that. You'll get far better reliability from it and be able to do greater things with it and you'll end up spending only slightly more for the new block. If you can sell your old one so much the better.

    We'll finally get to see dyno results on my old car in the near future. The new owner was already down at RS to tune but their laptop couldn't read from the E6K properly so he had to come back later. I'm kinda curious just to see what my numbers were from the rough tune Todd and I did for it.
     
  8. readymix
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    readymix ...Lest ye be trod upon... Staff Member

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    Hey, when you blow your motor, can you sell me your crankshaft?
     
  9. Yang
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    Yang Well-Known Member

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    I may have one soon :lol:
     
  10. readymix
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    readymix ...Lest ye be trod upon... Staff Member

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    2.5L Phase 1 Crankshaft?
     
  11. Dynapar
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    Dynapar Well-Known Member

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    it sounds like 6 is what works the best. however with proper tuning / hardware you can do 10. although from what i have heard 8 works the best as far as $$$/Power goes. since you can caress the extra 2 psi fairly easily, and without major issue (so i hear).
     
  12. WRX1
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    WRX1 _ Staff Member

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    Ok, there is alot of mis-information going around. You can run 20psi, but you need to have PROPER EM. You need full control of your of your fueling AND timing. Remeber, the more boost you run the less timing you can run. So yes, you can run 20psi, but you timing is going to be VERY low. There is a happy place in the middle, and that will depend on all your supporting mods and em. Most rs's run 5-8 with fair em. Rallynavvie could have ran more boost with his haltec, but his ic was kinda holding him back. What ic are you running? What em are you running (or plan on running)??

    Russ
     
  13. snbrd4evr
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    snbrd4evr Well-Known Member

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    I can't tell if you're serious or just joking. I'm sure the motor could run 20 psi... for 10 seconds :lol:

    I have hit 9 psi in my car for a few full runs and it was ready to explode. I could feel the heat through the vents. Right now I'm running around 5-6 on wastegate and between 7-8 when the solenoid is turned on. Right now I have a hydra for engine management (it's a full standalone that's plug and play). I ran 4-5 psi for a long period of time just to get used to how tuning works and how the car will react to different changes.

    Before we can give you any good recommendations, you need to tell us what turbo you're running, what engine management, what intercooler, and what phase motor you have.
     
  14. FuJi K
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    FuJi K Well-Known Member

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    20psi with race gas is do-able with good engine management. It's just the rods and pictons will go boom just because they're not strong enough.

    You can go 16psi just fine with like said, godo tuning. There's been a few in the past that put 12psi and run 12's in the 1320.

    Get the fuel their and you'll be safe. It's just that when you're having that much pressure in the cylinders, the rod and pistons may not hold, even though you have good tuning....you might just throw a rod bearing.
     
  15. Bielke55
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    Bielke55 Well-Known Member

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    Wow thanks everyone for the help!! Im running a garrett T28BB. with custom everything basically. The Kit was not bolt-on like it said. For EM im using Hydra Nemesis and Ronnie as my dyno and tuner. im running at 4PSI right now. I ordered larger Fuel injectors because my stock ones are maxed out. Im having some boost leak problems though, cause at 1,200RPMs the boost is 6. But then at 5,500 it drops to 4. Its been one thing after another. Im looking for more parts if anyone is selling please let me know
     
  16. BlackDubRX
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    BlackDubRX New Member

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    I've run 35 psi on stock head studs/no EM but fuel. :lol:
    And yes, he is serious. There is no magical number that your car will explode at. Only if certain conditions are met, and lean is certainly one of them. It all really comes down to your setup.
     
  17. RallyNavvie
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    RallyNavvie Well-Known Member

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    You boost shouldn't even be coming on at 1200rpm. That's, like, 200rpm more than what my idle was set at.

    Also your stock RS injectors are NOT maxed out running less than 6psi. It was generally accepted that after 5psi you look to larger injectors, and even then you don't need to go crazy on massive ones. If you're keeping it to around 10psi then perhaps 350cc injectors should work. Best thing you can do is have an engine computer that supports staged injectors ;)

    And as for running 20lbs on the stock 10.5:1 RS plant I'm pretty sure no amount of tuning, unless it's firing when the exhaust valves are open, would allow that motor to survive. I mean there is a limit to what the engine internals can take. I think I recall seeing someone run 12psi on stock internals with a Link ECU but even that one went after a few months. As I said, I would steer clear of anything more than 8-10psi on stock internals and only then with proper engine management (i.e. no piggybacks).
     
  18. snbrd4evr
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    snbrd4evr Well-Known Member

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    You've run 35 psi on a stock 2.5RS block and it didn't explode? From what I've always read, if you want to drive your car daily you should run at most 6psi if you have a rrfpr and a voltage clamp, or run 8-10 psi if you're running a standalone. Even 8-10 is pushing it, the block isn't strong at all and is known to warp the cylinder walls under high boost and blow the rings out.

    You have good engine mangement and a good turbo, I'd suggest running 6-7 for a while and have it tuned. What injectors are you planning on running? I'm running RC550's and they're doing well even for brief moments around 8 psi. Good luck with everything and I hope we all helped helped you.
     
  19. AWDimprezaL
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    AWDimprezaL has more posts than you

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    kelly your car is wicked, the backfires rule pretty well too
     
  20. WRX1
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    WRX1 _ Staff Member

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    you need to remember that turbo diesel's are around 20-25:1 compressions and are running 35-80psi of boost. I also never said at 20psi you would be able to run 20 degrees of advance. Like I said, there is a happy medium between boost and timing that needs to be found. If you read up on some of the tunning posts you will see that some people run alot of boost and a little timing and other are the complete opposite.

    Russ
     
  21. snbrd4evr
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    snbrd4evr Well-Known Member

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    Very true, but this block isn't strong enough to handle 20 psi even if the timing is retarded down to 8 or something. It's a matter of the internals holding the pressure. I could see 20 psi in one short burst. But with these blocks, it's just smarter to run 6-8 psi and retard the timing a little bit if you're going to be using it as a daily driver. If you don't believe me, you should check out some of the threads over on rs25.com, anything over 10 psi lasted less than half a year and that was with crazy tuning. I'm not saying you're completely wrong, just that it's not very smart to try to run a stock 2.5RS block at 20 psi daily.

    Thanks :D
     
  22. Bielke55
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    Bielke55 Well-Known Member

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    So in case anyone is curious ever... 10 PSI on a N/A 251 Block is PUSHING the limits of the block...
     
  23. AWDimprezaL
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    AWDimprezaL has more posts than you

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    Ahahahahahaa
     
  24. snbrd4evr
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    snbrd4evr Well-Known Member

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    I was right!!! :laugh:
     
  25. Shibbs
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    Shibbs The Daywalker

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    lol 3+ year bump.
     
  26. qstarin
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    qstarin Well-Known Member

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    def nice bump!
     
  27. RallyNavvie
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    RallyNavvie Well-Known Member

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    And yet I don't miss that turbo RS of mine at all, every day wondering if this was the day I was going to shred the transmission. Oh wait I do miss it :)
     
  28. RichWRX
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    RichWRX Well-Known Member

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    30lbs :)
     
  29. ShortytheFirefighter
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    ShortytheFirefighter Pokemans. I has none. Staff Member

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    DING!

    Fries are done!

    So, catastropic failure or what?
     
  30. AWDimprezaL
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    AWDimprezaL has more posts than you

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    It still ran, with part of a piston. Furthermore that piston was completely washed? cracked head perhaps?
     
  31. Bielke55
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    Bielke55 Well-Known Member

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    [​IMG]
     
  32. RallyNavvie
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    RallyNavvie Well-Known Member

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    Epic.
     
  33. ShortytheFirefighter
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    ShortytheFirefighter Pokemans. I has none. Staff Member

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    (whistle)

    Ouchie. How bad is the head on that side?
     
  34. Bielke55
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    Bielke55 Well-Known Member

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    Head and valves were just fine. It was weird there was nothing to be found...
     
  35. blackozone
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    blackozone Well-Known Member

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    LOL! Piston bits, NOM NOM NOM!!!
     
  36. ShortytheFirefighter
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    ShortytheFirefighter Pokemans. I has none. Staff Member

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    Wow. That's insane.

    I have to wonder where that chunk went.
     
  37. Bielke55
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    Bielke55 Well-Known Member

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    My guess is that it exploded into small enough pieces and passed through the valves and through an opened wastegate
     
  38. Snowbum
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    Snowbum Well-Known Member

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    I wonder what noises you'd hear if the wastegate was closed :)

    LOL Nice bump doood!!
     
  39. wrexinator03
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    wrexinator03 Banana Cream

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    BOOMmm