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BMW E30 M50B25 Turbo (EMU) from Austria

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Hi,my name is Marco, I´m 28, father of a lovely 2 year old daughter and 2 week old son, mechanic as profession and crazy about cars ;). At the moment I´m tuning my BMW E30 M50B25 Turbo (which was NA first) and I manufactured and built almost everything on my own. I´m completely new to the tuning stuff, but I´m willing to learn and very interested.So please forgive me, if I´m asking novice questions, even if I took a few courses already ;)

For now, I´m road tuning only. What I achieved so far:

- good starting with different temperatures

- stable lambda values under load

- good drivability for everyday driving up to 180 kPa

What I have to achieve yet:

- Working 3 wire PWM idle control

- stable lambda under idle

- getting on a dyno for fine tuning of ignition

- closed loop lambda control

- closed loop boost control up to 220 kPa

- launch control and banging flames out of exhaust just for fun^^

- and much more..

Some details to my project:

I own the E30 for over 6 years now and upgraded a lot of parts during these years. For example E46 steering, PU bushes everywhere, bigger brakes and Bilstein B12 suspension, N/A E36 engine with now forced induction and so on. It is, as usual, a never ending project^^. I finished most of the essential mechanical turbo adaptions just a couple of weeks ago, so I was´t able to drive more than a few hundred kilometres since then.

Engine details:

- 2,5l straight 6 with stock internals

- ARP head studs

- O-ringed block (via groove o matic 100GR) with OEM head gasket

- 8,5:1 compression (instead of 10:1) with milled OEM pistons

- ACL main and conrod bearings

- S50B30 oil filter housing with DASH fittings for oil cooler

- custom exhaust manifold and downpipe (one of the few things I haven´t done by myself)

- 3" exhaust piping with 2 absorption mufflers

- EMU Ecumaster standalone (with Bosch LSU 4.2, EGT,...)

- Siemens Deka 630ccm injectors

- Bosch 044 pressure pump

Boost details:

- Airwerks S200SX twin scroll turbo (Ar: 0,83, 46mm comp inducer)

- Tial 44 wastegate (0,5 bar spring for now)

- MAC valve for boost control

- Greddy FV BOV

- custom 2,5" piping

- hoonbrothers 600x300x76mm intercooler

Drivetrain details:

- E34 M5 S38B36 flywheel (milled and with M50 starter wreath)

- E36 M3 S50B30 Sachs 4 pad sinter racing clutch

- E36 325i M50B25 transmission and prop shaft

- E30 3,25:1 limited slip diff


I´m a friend of pics so here we go :D

Drifting is one of my passions!

Some of the parts I used for the turbo built:

I used the OEM loom, stripped everything I don´t need away and modified it. If I`d do it again, I would make a new one, instead of using the OEM.

oldschool wiring diagram drawn by myself :D

Cleaned all the internals and valves:

Measured the combustion chamber volume:

O ringing the block:

Milled OEM pistons to lower CR from 10:1 to 8,5:1:


Turbo drain into the timing chain housing:

Custom catch tank for crankcase ventilation:

My manifold, downpipe and wastegate piping from Bulgaria:

The whole thing is now heat wrapped.

Custom intercooler piping:

Custom fuel catch tank. Unwisely I placed it in the engine bay.. One more thing I´ll change in the future.

Custom 3" stainless steel exhaust:

As heat is a big issue, I tried to reduce and keep it away from everything important:

To dos for winter:

- air filter relocation to bottom front

- engine compartment heat management improvement :D

- IAT sensor relocation from intake manifold, to charge piping right before throttle

- EGT sensor relocation from downpipe to piping of cylinder 6 in exhaust manifold

- front strut bar

- starting with chassis/ rust repair

- as long as it´s not too cold: tuning! :D

Two questions for now:

1) I do have a significant boost drop in the higher rpm ranges which can´t be overcome with duty cycle boost control. Best seen in third gear and above:

Boost reaches maximum of 160kPa at about 3500rpm and then drops continuously to 140kPa at 6500rpm. With duty cycle boost control, I reach 190kPa, dropping to 150kPa. I couldn't find boost leaks and the BOV is set to hard.

May the turbo be too small, so that I get into choke? Hard to believe, as I´m surely not pushing over 300hp now.. Unfortunately I can´t get a compressor map for my 0,83 Ar, only for the 1,22.. Any other ideas?

2) My lambda value at idle starts to jump around 0,95 to 1,1 when the CLT is over 80°C.. At first I thought of a leaking head gasket, but thats not the case. Pressure loss test on each cylinder is under 2%, therefor very good. What could cause this?

Nice build there - Great work!

I'm not familiar with the turbo you're using but I suspect it might be a touch on the small side. I'd guess that your exhaust back pressure might be getting pretty high which will then be forcing your wastegate open by virtue of the soft wastegate spring you're running. I'd try running a harder spring in the wastegate and that may help but when you see the boost falling over at high rpm it's usually an indicator that the back pressure is excessive.

I don't have a firm answer for what is causing your inconsistent lambda. This can be caused by mechanical aspects such as poor valve seating or air leaks into the exhaust system. It could also happen if you're trying to drive the injectors at a pulsewidth that's too low for them to reliably operate.

Thanks a lot for the praise and the fast answer! :)

Backpressure due to the small Ar is a good hint! I should have thought of it on my own after watching the courses^^. I´ll try a harder spring.

Valve seating shouldn´t be an issue, as I sanded (?) them when the engine was disassembled. Also the pressure loss test showed great values. Same on all 6 cylinders:

Pulsewidth is 1,2ms.. Is that not enough?

Air leaks in the exhaust system.. I´ll check that!


Nice work Marko , i love an E30

Thanks! :)

I installed a 0.9 bar wastegate spring instead of the 0.6 bar. It now holds the boost up for about 300 rpm longer, but then again, dropping to almost 0.5 bar at 7000 rpm. So this means to be due to the "small" turbocharger?

Hi, I tried something different now:

I measured the boost directly after the turbo and realized, that there the pressure is 20-30kPa higher than MAP, but that should be because of my 600x300x76mm intercooler. And I have no big differences in high rpm ranges, as I should have if there is a leak somewhere.

Then I disconnected the wastegate hose and set fuel cut at 210kPa (0,9bar wastegate spring). In first and second gear, I won´t get more than 170kPa, as the engine is revving faster than the turbo can set the system under pressure (I think?). In third gear, fuel cut occurs at 3800rpm. BUT if I rev slow to about 4500rpm and then floor it, the pressure won´t rise beyond 170kPa, it pretty much reacts the same as if I had the wastegate hose connected.

That means my turbo really does have difficulties handling the amount of exhaust gases? I can hardly believe this, as the same turbo with Ar of 1,22 instead of my 0,83 can push 580hp (says Airwerks) and I´m far away of even 400hp..?

You need to run a boost solenoid and get closed loop working. As flow increases you need more turbine energy to maintain the same boost, the only way to do this is increase exhaust manifold pressure to the turbine if the combined diaphragm and manifold pressure is opening the gate at higher rpm/flow you need to bleed a bit from the diaphragm at high rpm with a solenoid, a less desirable technique tham PWM if your outputs are limited would be a simple digital output triggering a solenoid to a small orifice or "boost T" at high rpm when it starts to drop off. The BW turbos generally have a relatively large turbine for compressor so I think you should be ok there, it is just what happens.

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