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Old 08-28-2018, 12:05 AM   #1
Littleman1
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Turbo M20B27

I just got an E30 325e and i am displeased with the lack of power and i was looking into a turbocharger or other forced induction builds.

Ive been looking around the forums and haven't found anything directly addressing how much boost a stock AND fully built M20B27 "Stroker" can handle

Ive been looking around for turbo sizes too, and would like to know what the biggest turbo would fit under the hood.
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Old 08-28-2018, 04:52 AM   #2
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The FAQ/DIY section is for staff-approved instructional posts only. Please do not ask questions there. If you don't know where to ask your question, post it in General Technical and we'll move it to the appropriate subforum if necessary. Thanks in advance.
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would be in depending on tip slant and tube size
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Old 09-04-2018, 05:02 AM   #3
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Space is not the limiting factor. You can cram turbos that are way too big for the engine in there. With appropriate modifications, it's possible to make well over 1000bhp on a turbo M20.

That said, I don't think you're asking the right questions here. You need to define your goal, and then ask the questions to get to that goal. Are you looking to drag race? Autocross? Just want it to be more fun to drive? What's your budget?
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Old 10-14-2018, 11:50 AM   #4
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Iím on a stock bottom end with gapped rings, built head and making 440whp on an m20. Good tune and itíll hold.
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Old 10-14-2018, 01:59 PM   #5
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Yeah, I'll echo that. Reason why most fail is because once they 'get boost' they think it's a ticket to shoot for the moon by pushing the envelope. No, pick a goal and build your engine towards that goal in mind.
'What's the biggest' and 'how much can this engine handle' isn't the right approach lol.
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Old 10-15-2018, 12:09 AM   #6
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Well I'm only asking because I don't have a set goal I just want to know that the maximum possible and base my goal of that set amount. Recently I have sort of set a goal of 285hp. Now that I have a goal "even though it's low" what would I need to do to get to that goal. Parts and tune recommendations appreciated
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Old 10-15-2018, 12:10 AM   #7
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I'll more than likely increase that as time goes on I'm just trying to start somewhere.
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Old 10-15-2018, 08:10 AM   #8
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Originally Posted by Littleman1 View Post
Well I'm only asking because I don't have a set goal I just want to know that the maximum possible and base my goal of that set amount. Recently I have sort of set a goal of 285hp. Now that I have a goal "even though it's low" what would I need to do to get to that goal. Parts and tune recommendations appreciated


285 is very obtainable. Letís start with your budget.


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Old 10-24-2018, 02:48 PM   #9
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Hey guys, don't mean to thread jack, but I have very similar questions to Littleman1 and figured it would be better then starting a new thread.

What sort of turbo do you guys recommend for a street car, with the best possible throttle response, with a goal of 350-400whp?

My buddy that has turboed lots of things is trying to get me to go with a Precision 6262 gen 2. I have herd lots of guys have had good results on the 2.7 with the smallest HX35 that's externally gated?

My car is a 1985 325e, and I just did an 885 head swap with new valve guides, valve job, ARP head studs, OEM BMW head gasket, new piston rings, rod bearings, and a Bimmer Heads 274 cam. I live very close to SSSQuid and he will be doing my turning.
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Old 10-24-2018, 03:11 PM   #10
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Hey guys, don't mean to thread jack, but I have very similar questions to Littleman1 and figured it would be better then starting a new thread.

What sort of turbo do you guys recommend for a street car, with the best possible throttle response, with a goal of 350-400whp?

My buddy that has turboed lots of things is trying to get me to go with a Precision 6262 gen 2. I have herd lots of guys have had good results on the 2.7 with the smallest HX35 that's externally gated?

My car is a 1985 325e, and I just did an 885 head swap with new valve guides, valve job, ARP head studs, OEM BMW head gasket, new piston rings, rod bearings, and a Bimmer Heads 274 cam. I live very close to SSSQuid and he will be doing my turning.


6262 is a good turbo and will get you to your goal.
I would gap your rings for longevity.


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Old 10-25-2018, 12:05 AM   #11
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Budget less than 3,000 and I want it to still be street "usable" I live in. A place with lots of snow so I need it to not have crazy amount of turbo lag that would break my wheels free. It still needs to be usable power.

Eventually I will build the crap out of it. But for now 280-380hp

Last edited by Littleman1; 10-25-2018 at 12:23 AM.
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Old 10-25-2018, 12:08 AM   #12
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I was thinking a compound turbo set up (like a Cummins) to build boost fast and be less prone to lag due to the fact it revs and runs like a diesel

#5000 rpm redline

Pls recommend turbo sizes, injector sizes, exhaust setup, ecu tune, comp ratio, heads, cylinders, pistons/rods, valve springs. Whatever you know that could be usefull

Last edited by Littleman1; 10-25-2018 at 12:19 AM.
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Old 10-25-2018, 07:22 AM   #13
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Problem with compounding is you will blow your budget.
Diesel turbos are slow spool, high boost unless youíre getting a TDI turbo.


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Old 10-25-2018, 05:47 PM   #14
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Quote:
Originally Posted by Littleman1 View Post
I was thinking a compound turbo set up (like a Cummins) to build boost fast and be less prone to lag due to the fact it revs and runs like a diesel

#5000 rpm redline

Pls recommend turbo sizes, injector sizes, exhaust setup, ecu tune, comp ratio, heads, cylinders, pistons/rods, valve springs. Whatever you know that could be usefull
Are you intending to run the stock eta head and cam? I assume so since you're talking about 5000rpm redline. I don't think people really bother with that. Poor flow, weak valve springs. Also even a "small" holset likely is only going to spool right at the top of your rev range. My hx35 w/12mm hot side spools fully around 3500 rpm on a 2.5 for reference.

On top of that, you'll need to convert to a Motronic 1.1 harness at least to run any popular PNP standalone ecus.

It seems like the typical formula when starting with an eta is bare minimum 885 head and motronic upgrade. Then all the standard turbo build parts: MS, injectors, BOV and wastegate, blah blah blah

A lot of people will say take whatever you think your budget is going to be and double it. They're basically right. I went as "budget" as one could with used parts, great craigslist deals, etc...and am into it for way more than I initially thought. The little stuff will nickle and dime you and the big things are big. (like your ECU) $3k is optimistic.

Also as far as I know, Cummins are all single turbo- some variation of Holset. A lot of people run compound setups but they don't come that way from the factory. Just a note.

Good luck!
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Old 10-26-2018, 12:08 AM   #15
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Thanks fror the info I'll try to keep it simple and do something along the lines of a 6262 turbo and try to keep things as stock as possible. I'm not trying to turn it into a monster (yet) so I would assume stock head with better injectors and a new ecu and other things would do me well.
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