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  1. #1
    Boost-A-Holic's Avatar
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    Max HP on stock block 09 RXP????

    Lets say i just wanted to slap an aftermarket SC on my 09 RXP with the supporting mods needed (intake, exhaust, injectors, tune, IC), leaving the engine internals bone stock. How much power will it take still maintaing reliability? I dont wanna push it to hard.


  2. #2
    Sayers's Avatar
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    What SC you looking at?
    What RPM do you plan on running?

  3. #3

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    Quote Originally Posted by Boost-A-Holic View Post
    Lets say i just wanted to slap an aftermarket SC on my 09 RXP with the supporting mods needed (intake, exhaust, injectors, tune, IC), leaving the engine internals bone stock. How much power will it take still maintaing reliability? I dont wanna push it to hard.


    http://www.gurneyflap.com/bmwturbof1engine.html



    The above link is about restoration of a 1.5 liter turbo engine used in F-1 that makes 802 HP @ 9700 rpm in race trim @47.0 psi, for qualifying turning up the boost it made 1,300 [email protected] 81-psi

    A few items to note:
    The power curve starts at 7000 rpm this makes it unusable in a PWC that uses a full time power connection to the jet pump
    At 8200 rpm (stock 4-tech limit) the HP of the BMW is only 366
    At 9400 rpm (modified 4-tech limit) the HP of the BMW is 749
    Bore and stroke = 89.2 mm x 60.0 mm (4-tec has bxs = 100.0 mm x 63.4 mm)


    This is not a sophisticated motor, the basic design was used in 1961 BMW passenger cars, IMO the 4-tec has similar maximum HP potential or better (the 4-tec has a shorter bore/stroke ratio thus higher RPM potential) but with the use of modern stand alone ECU's still be able to retain the low end power required for PWC use.

    With 45-psi turbo boost on E85 one could get about 600 to 700-hp @ 8200-rpm out of an unmodified 4-tec, the slow burn E85 would not push it too hard, power potential is actually greater since unlimited cooling is available

    You would need injectors larger than 200 lb/hr and a stand alone ECU tuned for E-85, modified external cooling, biggest oil cooler available, 20-70 racing synthetic oil, thru hull exhaust, fabricated intake, a huge turbo with small exhaust housing (more study required)

    There is no aftermarket supercharger available that would come close to pushing the limits of an unmodified 4-tec running at only 8200 rpm. With a turbo one can go much bigger; note in the pictures on the link the huge twin scroll turbo big enough to run a diesel truck

    The only way to get boost up to 30psi ++ at under 8200-rpm with a SC is go with a belt drive roots or vortec designed for 5.0 L size motors.
    I do not know how to modify 4-tec for a belt drive, besides a high boost SC would eat up HP and fuel like no tomorrow (needs to put out 900hp to make 700-hp net)

    In other words the bone stock 4-tec internals are rpm limited not boost limited, the problem is finding a charger that will make a decent amount boost with the stock pto drive
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    Last edited by ticat928; 08-08-2012 at 10:41 AM. Reason: clarification

  4. #4
    boost junkie skidoochris's Avatar
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    IMO safe HP is in the 400 range and 30psi is on the edge for stock rods
    thats with a full stand alone not some ones map stuck in the stock ecu

  5. #5
    Boost-A-Holic's Avatar
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    Quote Originally Posted by ticat928 View Post
    http://www.gurneyflap.com/bmwturbof1engine.html




    In other words the bone stock 4-tec internals are rpm limited not boost limited, the problem is finding a charger that will make a decent amount boost with the stock pto drive
    i didnt know that thats interesting. And sayers i honestly havent looked into it too much i was thinkin maybe a 2rude. So if im limited by my rpms rather than boost is there a way i can crank up the boost on the stock SC? Im currently running a Riva gen2 impeller so im close to 10lbs @8150 right now. Im sure if i change out the IC and intake/exhaust than it will get an extra lb or two cuz more airflow. Do they offer a boost controller so i could maybe max out the stock SC before i upgrade later down the road?

  6. #6
    boost junkie skidoochris's Avatar
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    SC's are rpm controlled, they are not adjustable
    if you want more boost, you need more rpm's or a differant SC compressor wheel

  7. #7
    JFizzleJR's Avatar
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    or more/cooler air flow

    Quote Originally Posted by skidoochris View Post
    SC's are rpm controlled, they are not adjustable
    if you want more boost, you need more rpm's or a differant SC compressor wheel

  8. #8
    Boost-A-Holic's Avatar
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    gotchya

  9. #9
    i hate my bipolar disorder its great
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    generally hp doesnt kill internals, its pinging or excessive rpm

  10. #10
    Moderator Snoman's Avatar
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    Quote Originally Posted by Boost-A-Holic View Post
    Lets say i just wanted to slap an aftermarket SC on my 09 RXP with the supporting mods needed (intake, exhaust, injectors, tune, IC), leaving the engine internals bone stock. I dont wanna push it to hard.
    With those little mods you have nothing to worry about... You wont even be close to 300hp....

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