Looking for Parts Recommendations on E34 M50B25NV Turbo Build

[fastback180]

Came across a 1991 525i with the ZF 5 Speed Manual trans and couldn't pass up the deal! ($2k)

It has a really low quality turbo set up on already from the previous owner and its horrendously set up.. So I am starting over completely from top to bottom with it and want to do this up nice with some name brand parts.

It is my first "Turbo" build so I don't know a ton on the subject but I am a very well rounded fabricator in the off-road world so the custom fabrication part of this build is the easy part for me.

-The car has already been converted to OBD2 engine harness and has a megasquirt pnp ECU
-Just got my cut ring/copper spacer gasket from CES Motorsport & ARP Stud Kit

I know the basics of boosting a car and the supporting fuel/oiling modifications required but very confused with what are good manifolds and the turbo/wastegate sizing I should run for this engine to make peak power.

Also been eye balling the VAC Mild turbo cams and valve springs as well.. Are they worth it?

Shooting for 550WHP or basically what ever the stock bottom end can handle. Any tips would be greatly appreciated!

[Sio2crew]

2.5 liter , I would guess something similar to a gen 1 gt35. ( 62/62) seems like the go to for 500-600 h.p. on a 2.8 or a 3.2. (With high exhaust manifold pressure) If I had a 2.5 I would go g35-900., or mabye a gtx3576? From all the research I have done , most struggle to get over 500 hp with turbos smaller than 62mm inducer /exducer. (Again on 2.8 to 3.2 liter ) I know my tuner said it took almost 30 psi to get 600hp on a 3.0L 3576 set up. ( 58/62? Cant recall)

I think a 62mm turbine exducer is about right on a 2.5 . I think a 64 or 66mm turbine exducer is right on a 2.8 +



Once you get over 500 hp the emap goes up a lot. 20 psi boost will have 40psi emap with a gtx3582 s52. (3.2L e36 m3 )

The weak link seems to be broken ringlands on the stock bottom end. Or bent rods if you make 450+ t.q. before 4,000rpm.

Bigger turbine will give you more power later. But less back pressure. Bigger turbine will give the ringlands less heat.

Here is a 2.5 with a 62/66 pte. (Edit its a 62/62 pte. Looks like it makes power above 4000)





That e34 had no vanos control/ not in use. Should be similar to a non vanos car. It also has the wastegate re enter the exhaust at a funny angle for some reason? (No set up is perfect, as the o.p. already knows. )

Seems like everyone wants boost before 4000 rpm. But thoes builds usually break something.

E85 builds seem to last way longer (less heat)

I went ape flex fuel kit on my stock ms43 s52 turbo. ( gtx3582 gen 2 66/62) I also have j.e. pistons and eagle rods, cut ring , 625+ ect. if you can run e85 or flex, its worth it on these engines.

Wish i had more personal experience with the 2.5. If its non vanos, its got the bigger rods, and bigger valve stems, and nested dual valve springs. Good canidate for solid lifters / higher rpm power. Someguy325 has build threads for the non vanos head... worth a read. (Including adding vanos to a non vanos car)

https://www.bimmerforums.com/forum/s...ge2&styleid=51

Mabye gap your rings if you want longevity?

I spent soooo much time on turbo slection. All my turbos are pulsar brand. (Lots of good luck with them in the past) I originaly got a 3576 for my zhp m54b30 /spacer/mls /raceware studs. Looking for 450/500 hp ..... Then I built the s52 so the m54 stits on a stand still. . Went to a gtx 3584 gen 3 pulsar (on sale) its a gtx3584 67mm compressor and center section. Its a pte 66mm turbine blade fit in the hotside. Seems like the right choice for 600s to the tire. Lots more reading, knowing I want sub 4000 spool, I got a 3582 gen 2 to start with on the s52. I really wanted to try a g35-900, however a lot of places claim they wont make the advertised power. (Real street says they tap out before 600 to the tire. 2jz?)

To each their own. This is only scratching the surface of my opinions. The 3582 ( gen 2 .82 ar hot side. ) feels about right so far. Power comes in by 3500.

IF you went solid lifters / high rpm. You would need a bigger turbo to keep up with high rpm flow.

What is your intended use for this car? Street car? Highway car? Auto cross? Use will influence turbo choice. I put my s52 in a e39 touring, for highway travel. The big turbo makes sense.

Im using a rapid spool manifold ( the 3 to 2 to 1 style ) If i had it to do over I would 100% go twin scroll. If you can get or make a twin scroll DO THAT!! (The best way to make a big turbo feel smaller , and a small engine feel bigger. )
I actually am thinking about making my rapid spool into a twin scroll. Would be real easy and let me keep my a.c. still. K64 makes a twin scroll that keeps a.c. and isnt too expensive. The other twin scroll options are pricy. Pulsar does offer twin scroll housings on their turbos (.85ar)

I do believe people swap the pistons/rods/crank from the 2.8 m52 into the m50. Or the 3.0 build by taking the rods/pistons/crank out of a m54b30 engine. M54b30 crank has the same part number as a s52. ( m54 has a different ring set up. 2 rings on a m54. 3 rings on a m52. M54's are know to burn oil by comparison. )

Only other big money item will be your clutch choice. ( assuming your rear end and driveshaft are still happy. )

[fastback180]

Ive watched all of his videos haha

This car is primarily going to be used on the freeway and curvy back roads. I live about 30 min straight north of Phoenix, AZ with lots of open roads around. Closest stop light to my house is probably 10+ miles away. lol

I would love to pull the engine and open up the ring end gaps but I have a problem of going way overboard on projects like this and getting way deeper into stuff then I should be to accomplish what I wanted in the first place in a timely fashion.. If I pull a perfectly good bottom end out of this car, I will end up with a full forged crazy flame breathing monster 2 years later. I want this done before the end of summer haha

I was looking at the Pulsars and seemed to be a good buy but funny you say the 3582 because I just said screw it right after I posted this and pulled the trigger on an eBay GTX3582 Gen 2 purely for pricing with the intension of doing a name brand BW or PTE once I get a better handle of what the car is like to actually drive and I can make an informed decision on how I should spend $1500 or what ever.. I am sure this turbo will be on the big side but like you said, it will give me room to grow and wont create too much down low power that will cause bottom end problems.

I am 100% doing E85. I have a station that's about 25 min from my house as well.

I love having a violent powerband. I have more fun driving something that you have wrap out then something that makes smooth power predictable power in the lower rpms. Which is why I am interested in cams and probably valve springs. Solid Lifters are a little over the top of what I am trying to achieve right now I think.

How do you like the rapid spool? I think I am going to order that this week. Ive read other good things about it as well.

Car already has an aftermarket clutch in it with poly engine/trans mounts so I'm literally not going to touch the drivetrain other then basic service/fuild change and maybe some rear diff mount stiffening down the road.

[Sio2crew]

No drama with the rapid spool.
Only real complaint is that the hole for your turbo flange is neither a t3 or a t4. A t3 gasket will crush funny right on the gasket ridge/manifold lip. I bought a second t4 .8x housing to replace my t3 .8x housing. Just because the fitment looked that wack.

The hole is t3 length one way. T4 length the other way. A.k.a. two opposed sides are t3 two are t4

They are suposed to sound the best ? Moot point and I dont have much to compare it too.

I also cut the long flange once , so its two equal 3 hole flanges now. I wouldent do that tho just because they shifted 1/16th of a inch with only one pipe holding the two halves together now. Still no leaks no drama. Pulls bolth halves flat when mounted. Ive got it covered with heat wrap so that may overheat the thing eventually? I dont get too much repeated pulls tho. Its a rare event if im doing big pulls back to back.

Seems like you have it figured out. E85 and open roads, sounds like a good match.