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    M52B25TU Turbo build - Need some help!

    Hi - I'm new to this forum and appreciate all answers!

    I own a '99 BMW 523i with an M52B25TU engine mated to a ZF 5HP19 (A5S 325Z - TW) automatic transmission. I'm doing a turbo build on this engine and have quite a few questions about this. I what answers from people who have experience with these builds, and not from those of you who knows a guy who knows a guy!

    I'm doing this build with a colleague of mine who has done tons of turbo builds before, but never on an M52. So my question is not related to the actual build, but to the M52 itself.

    My goal is around 300 C/HP running 11PSI/0,75BAR, but the tricky part is that we are not going to lower compression. Does anybody know if this engine can handle 11PSI at stock compression? If not how much boost can an M52B25TU handle on stock compression? My colleague says we can safely 7PSI/0,5BAR on stock compression, but that's not more that about 250 C/HP, and I simply what more! He says that 7PSI is a general rule when boosting a N/A engine on stock compression, I don't doubt that, but I want to hear from you guys who have experience with this engine how much it can handle.

    Further does anybody have experience boosting an automatic M52? Does it work well?

    Looking forward to your answers!

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    Why not just use a thicker head gasket like many do successfully on the M52 and run even more boost safely?

    Not sure what the automatic can handle but I don't recall it being too beefy.

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    I dont think you need to tear into the engine and lower the compression to run 11 psi. But let one of the E36 pro's chime in, I am not sure about that.
    Some people live long, meaningful lives.

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    Click here to enlarge

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    Because it's a big and grueling job according to my colleagues changing the head gaskets on these engines, and if we can safely run 11PSI on stock compression why change the head gasket? Also I don't want more than 300C/HP or more specific 260-295 ft-lbs of torque because of my transmission. According to ZF the transmission can handle 240 ft-lbs, so my plan is mounting a bigger oil cooler on the trans and an oil temp gauge. In the future I plan on a manual swap, at that point I'll also change the head gasket and turn up boost. For now though, my first post is my plan.

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    Click here to enlarge Originally Posted by RiisFalch Click here to enlarge
    and if we can safely run 11PSI on stock compression why change the head gasket?
    So you can run more without building the motor?

    Click here to enlarge Originally Posted by RiisFalch Click here to enlarge
    Also I don't want more than 300C/HP or more specific 260-295 ft-lbs of torque because of my transmission
    True. Eventually you will though.

    You will make much more than 300 hp with 11 psi though so I wouldn't even worry about it as if your goal is 300 you will likely be running less boost.

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    "So you can run more without building the motor?"

    I'm not saying we can safely run 11PSI, I'm asking if it is possible to run 11PSI on stock compression I don't see the point of changing the head gasket....


    "You will make much more than 300 hp with 11 psi though so I wouldn't even worry about it as if your goal is 300 you will likely be running less boost. "

    How much boost do you reckon I need to run to hit 300 hp?

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    Click here to enlarge Originally Posted by RiisFalch Click here to enlarge
    How much boost do you reckon I need to run to hit 300 hp?
    It depends on the turbo, supporting mods, etc., but definitely not 11 psi at the stock compression.

    You will more than meet your goal on the stock internals of 300 horsepower.

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    7-8psi should get you there...

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    Click here to enlarge Originally Posted by Matt@Camber-Toe Click here to enlarge
    7-8psi should get you there...
    Thanks.

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    So you reckon 7-8 PSI will really give me around 300 hp?

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    Click here to enlarge Originally Posted by RiisFalch Click here to enlarge
    So you reckon 7-8 PSI will really give me around 300 hp?
    If not more.

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    On a low compression engine like mine it wont make that much more, but yours it should be fine to make 290hp give or take...

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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    If not more.
    Well that sounds great, then I'll hit my target!


    Click here to enlarge Originally Posted by Matt@Camber-Toe Click here to enlarge
    On a low compression engine like mine it wont make that much more, but yours it should be fine to make 290hp give or take...
    Well, that's right in the ball park of what I'm trying to hit!


    Thanks for all your replies. We're starting the build this week, so I'll let you guys know what numbers we hit after mapping and dyno runs.

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    At work today my colleague lifted my car up and took a look at the engine bay. As metioned before he's done many Turbo builds, but never on an M52 or even an E39. To my disappointment he wasn't that positive as before, because it's really tight in the engine bay. It looks like a nightmare to remove the stock manifolds and mounting the turbo manifold looks even harder, not to mention the four lambda sensors and two catalys. Also there's the task of mounting the intercooler, it's looks really tight. I'm gonna mount an M5 front bumper, so I think there will be room for one then.

    I'm still quite optimistic about the build, and think his worries are only matter of will and time.

    What do you guys make of these challenges?

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    Click here to enlarge Originally Posted by RiisFalch Click here to enlarge
    At work today my colleague lifted my car up and took a look at the engine bay. As metioned before he's done many Turbo builds, but never on an M52 or even an E39. To my disappointment he wasn't that positive as before, because it's really tight in the engine bay. It looks like a nightmare to remove the stock manifolds and mounting the turbo manifold looks even harder, not to mention the four lambda sensors and two catalys. Also there's the task of mounting the intercooler, it's looks really tight. I'm gonna mount an M5 front bumper, so I think there will be room for one then.

    I'm still quite optimistic about the build, and think his worries are only matter of will and time.

    What do you guys make of these challenges?
    M52 turbo builds have been done a million times. Sounds like you need someone more experienced.

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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    M52 turbo builds have been done a million times. Sounds like you need someone more experienced.
    Remember he is using a M52B25TU. Not the same motor from e36's. It has dual vanos and runs on a MS42 DME.

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    I believe Jon ( i forgot the username ) did a M52TU and swapped it into an E30. much tighter engine bay.

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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    M52 turbo builds have been done a million times. Sounds like you need someone more experienced.
    We'll you might be right. Problem is that where I live there aren't anyone I'm aware of who have done M52 turbo builds, nonetheless an M52TU build. So I've got to make do with what I've got. After talking with him today though he didn't seem negative anymore, but said it would probably take a whole day just to remove the exhaust manifolds and cat's.

    I also talked to a guy who writes/modifies ECU software, also known as chip tuning. I asked him about software for my car, and he said that it would require a complete rewrite do to mounting a turbo. He said that it wasn't task he was able to do either, and that I should try to get a hold finished software. That would imply getting hold of software from someone who has done a build like this before on this engine right? If so, where the heck would I get a hold of this?

    Click here to enlarge Originally Posted by Sorena Click here to enlarge
    I believe Jon ( i forgot the username ) did a M52TU and swapped it into an E30. much tighter engine bay.
    Would be great if I could contact this guy, I'll need all the help I can get Click here to enlarge I know talked to this guy the other day who has done an M20B25 turbo build, and took a look at his engine bay. He had a lot more space than I have, I mean my engine bay is very tight, but his was really spacious. I would guess that even an E30 engine bay is more spacious than mine.

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    Click here to enlarge Originally Posted by BoostAddict Click here to enlarge
    Remember he is using a M52B25TU. Not the same motor from e36's. It has dual vanos and runs on a MS42 DME.
    Yes, but turbo builds have been done on those as well.

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    Click here to enlarge Originally Posted by Sorena Click here to enlarge
    More like @NickG

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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Yes, but turbo builds have been done on those as well.
    I have yet to see a B25 on stock DME grant it I don't keep up on these cars anymore. Actually, I've only seen two M52TU builds. One I know somebody did using a Pectel Standalone, and the other was a B28 tuned by Active. AA made that tune some years ago when they did a custom turbo M54B30, and ran it on a MS42. NickG may have a tune for it too, idk. When I looked into he did not, but that was over a year ago.

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    Click here to enlarge Originally Posted by BoostAddict Click here to enlarge
    I have yet to see a B25 on stock DME grant it I don't keep up on these cars anymore. Actually, I've only seen two M52TU builds. One I know somebody did using a Pectel Standalone, and the other was a B28 tuned by Active. AA made that tune some years ago when they did a custom turbo M54B30, and ran it on a MS42. NickG may have a tune for it too, idk. When I looked into he did not, but that was over a year ago.
    He'll be the expert on the subject so I hope he chimes in.

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    i am the only person on this forum that i know of that has a m52tu turbo'd car. The only problem is that mine is a e46 323i and i think you are talking about a e36. The problems of the tight fit for me were addressed by using a custom built motor mount that integrated the turbo piping. It was extremely hard and took alot of time and reworking, but it can be done. If you are trying to get 300 chp no problem all day. But is it really worth it to spend all that money and time for 300chp when you can get a supercharger for that car sub 6000 and hit those goals! If you want to pick my brain pm me i would be happy to help

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    Click here to enlarge Originally Posted by BoostAddict Click here to enlarge
    I have yet to see a B25 on stock DME grant it I don't keep up on these cars anymore. Actually, I've only seen two M52TU builds. One I know somebody did using a Pectel Standalone, and the other was a B28 tuned by Active. AA made that tune some years ago when they did a custom turbo M54B30, and ran it on a MS42. NickG may have a tune for it too, idk. When I looked into he did not, but that was over a year ago.
    Are you referring to me as i used a pectel stand alone?

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