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E28 Turbo FAQ
Compliments of Brad D. @ www.mye28.com
Turbo e28 FAQ
-Brad Denton
Last revision 01/08/09
This FAQ is intended as a guide for those interested in venturing down the dark path of turbocharging. It is a very popular subject and many questions are hopefully answered within this FAQ. Hopefully it can be stickied for everyone's reference. I want to keep this page as accurate and current as possible and will gladly make any valid changes, corrections or additions if requested as I want this to be a quality document that guides new converts through their path to turbocharging their car. Please email me at bdenton180sx@removefirst_yahoo.com.
Where to buy a kit?
Turbocharging Dynamics or TCD sells a high quality bolt on kit that addresses all of the issues required to properly turbo your e28.
Cartech also still sells kits and components for the e28. Check them out here.
What other parts or kits can I use to turbo my car?
You can use parts from BMW's euro only 745i which came turbocharged. There were two engine variations, the m102 and the m106, and are very similar to a normal m30, but there are some small differences. Parts from either version will work to turbo your m30. At a minimum you will need the manifold, the turbo, wastegate and is very beneficial if you have the exhaust downpipe tubes. These parts would allow one to have the basic turbo components and buy the additional components similar to what would come in a new kit or used in a "roll your own" type setup. Better yet, having the entire 745i parts car would make the swap that much easier. It should be noted that the 745i manifold uses 10mm studs for mounting and a standard m30 head uses 8mm studs. The head will either need to be drilled and retapped or adapter studs used. For additional reading on everything 745i, Scottie Sharpe's website is a great resource.
http://bmwturbos.scottiesharpe.com/default.asp
Dinan also offered an m30 turbo kit. It is no longer offered, but occaisionally the used components come up for sale. For those who live in California, the Dinan kit is was and is the only kit that carries and CARB EO number so that it is emissions legal.
Recommended Reading and Relevant Information
There are several books that should be in a turbo enthusiast’s library. These books are great for the novice or the seasoned veteran.
Maximum Boost by Corky Bell.
Forced Induction Performance Tuning by A. Graham Bell.
Turbocharging Performance Handbook by Jeff Hartman.
Here are some other great website resources which include compressor map information as well as "turbo calculators"
Not2Fast Turbo Calculator and Glossary
Squirrel Performance Turbo Calculator
[rul=http://www.turbobygarrett.com] Garrett Turbochargers[/url]
Can both the M20 and M30 be turbocharged?
Yes, both m20 and m30 powered e28s can be turbocharged. Both engines respond well to turbocharging. There is a specific kit for the m30 powered e28 535i. TCD does not sell an e28 specific kit for the m20, but parts from the e30 325i can be utilized. TCD can advise the user how to proceed. Custom “homebrew” systems have been developed for both powerplants. Since the M20 in the e28 is the same engine as in 325e (and externally the same as the 325i powerplant) there is a wealth of information regarding turboing an M20 on www.e30tech.com whose turbo FAQ can be found here. Most other additional information regarding the M30 will try to be covered here.
How Much Power will my turbo e28 make?
Power levels vary greatly and are dependent on many factors. What octane fuel is being run? Is the car intercooled? What elevation is the car being operated at? From Corky Bell’s book Maximum Boost he cites that from his dyno testing he has seen output range from 0.052 bhp/ci psi to as much as 0.077 bhp/ci psi. For example an M30 has a displacement of approximately 213.6ci. So for 10psi gauge pressure (or 24.7 psi absolute)
you would have power figures similar to those seen below.
Lower Value - 0.052 bhp/ci psia x 213.6ci x (24.7 psia) = 274.3 bhp
Higher Value - 0.077 bhp/ci psia x 213.6ci x (24.7 psia) = 406.3 bhp
While these are theoretical approximations, they will get you in the ballpark to estimate you power output. Todd from TCD once mentioned that on many of the M30s that he had dynoed he will usually see the car put down roughly 12.5hp/psi at the wheels over the naturally aspirated hp. If an M30 makes roughly 155whp NA, then running 10psi boost, it will make 280whp. This estimation will also work fairly well for a turbod M20.
What internal modifications need to be made to the engine?
For many users no internal engine modifications will be required. Both engines are robust units that will tolerate a fair amount of addition power over stock. It seems that the stock M30 headgasket can reliably take 325-350whp with a safe tune. The headgasket can also be upgraded to a Multi Layer Steel (MLS) gasket. Proper RA or, roughness average is also very critical when upgrading as the MLS gasket. A RA of 20 is recommended. A stock head is reported to be in the 45-55 RA range. However, some have used a MLS gasket with head studs with little to no issues.
Stock rods should easily be up to the task in your turbod e28. I do not know of any reported rod failures in a sub 500hp m30. Pistons will also live if detonation is prevented. Power levels approaching 400whp have been accomplished on stock internals.
For those interested in calculating compression ratios of various m20 and m30 engines, you may find my Compression Ratio Calculators useful.
M30 Compression Ratio Calculator
M20 Compression Ratio Calculator
(Right click and Save As)
Where can I find a manifold for my car?
Turbocharging Dynamics ,666 Fabrication and Cartech offer new manifolds for both the m20 and the m30. The m30 can also use the 745i turbo manifold, turbo and wastegate. The m20 can use a modified 524td manifold which required porting of the runners and notching of the flanges to fit. It will accept a t3 footprint turbine housing, but typically required that the turbo be spaced away from the manifold to clear the valve cover. This can make spark plug replacement and valve adjustments difficult or impossible without turbo removal.
Mye28 user Turbodan tried to utilize a 666 Fabrication M20 manifold adapter and was unable to get it to work fit in the confines of the e28 chassis, therefore is NOT a viable manifold option.
There are also several people who have fabricated their own custom manifolds and adapters. The best material for construction is typically mild steel weld-els, typically 1.5”ID Schedule 40.. For reference the m30 cast iron manifolds can be flipped upside down so that a manifold adapter can be fabricated.
There are also a few other turbo manifolds that can be used which are worth mentioning. Dinan's cast manifold which was used in their turbo kit is flanged for a t4 turbo. Alpina offered at least two manifolds that I know of. These were for a single turbo and installed on their B7 series of cars. There was also their twin turbo manifolding used in the mighty e34 B10 TT. These rarely are available used, but they are out there.
What turbo do I use?
If you purchase a kit, it will come with a properly sized turbo for your application. If you wish to select your own turbo, it is highly recommended that you use calculations outlined in any of the above texts or use a turbo calculator software to determine your engines airflow requirements so that this data can be plotted out on a compressor map for verification.
With the influx of cheap Chinese turbos, it is common for someone to want to buy these as a basis for their system. While some have had decent results with them, it seems terribly hit or miss. Their specs are also seemingly very incorrect and misleading which is one more reason not to buy one.
Stay away from most “junkyard” turbos as they are typically way to small for either the M20 or M30. Most 80s vintage turbo cars were small trim t3 turbos and their compressors are way to small to support good power on either engine. Also the turbine housings will prove to be very restrictive limiting power.
A quality Garrett T04E (there are various trims available depending on desired power output) makes an excellent turbo for the M20 and M30. These can be had new for under $700 with your own specs. Garrett also offers a large variety of ball bearing units that are well suited to both engines.
There are a fair number of both m20 and m30 powered cars using Holset turbos with good results. These are typically found of Dodge Cummins powered trucks. There are several versions offered over the different model years. They are quality OE turbos but since compressor maps are scarce, your best resources are other Holset users.
Do I need an intercooler?
No, an intercooler is not required for low boost setups (10psi or less). Both air to air (A-A) and water to air (W-A) intecoolers can be used. TCD stage 2 kits come with a water to air unit. Cartech also offered an air to water unit that was integrated into the intake manifold. These are sometimes available used. All water to air units require the use of a pump, reservoir and additional front mounted heat exchanger for operation. They work very well and package nicely but add expense and an additional level of complexity to the system. A-A units are much simple in concept but typically require moderate to extreme sheet metal modification as well as more complex piping.
Where do I find a turbo back exhaust for my car?
At the time of this writing the only supplier for a pre-made turbo-specific exhaust for the e28 is TCD and is designed to work with their kit. However, any high performance e28 exhaust can be used however but may require modifications. Generally most use a single 3” diameter exhaust from the downpipe back.
A custom exhaust can also be fabricated using the muffler and high flow catalyst (we all know that you want to do the responsible thing 
) of your choice and roll your own. Use mandrel bent pipe to minimize restriction. There are many places online where you can purchase a variety of bends in mild steel and stainless.
How do I supply oil to my turbo?
Since all turbos, journal or ball bearing, require a clean, filtered oil supply from the engine. There are a few methods to accomplish the oil supply and drain. Oil can be tapped from the oil pressure sender location on both the m20 and the m30. These are in different locations on each engine, but both require a male 12mmx1.5 pitch to thread into either the block (m20) or the head (m30). You will want this to adapt to either an NPT or AN fitting so that an oil line can be routed to the turbo. A Braided -4AN line works well in this application. Some ball bearing turbos require an oil restrictor so confirm this with the turbo manufacturer.
The second method for the m30 is to drill and tap the oil filter housing so that an adapter fitting can be threaded in to the housing for attachment of the oil line. Shawn D.’s site outlines the procedure for drilling and tapping your housing.
The turbo drain is a critical part of the oil supply equation. If either the supply or return fails, your engine pumps out all of its oil potentially damaging your engine. It could also lead to an oil fire. Most people drill and tap the oil pan. This can be done with the oil pan in place. The recommended size for the fitting is ½ NPT, which requires a 45/64” drill. An image of a mounted drain from my car is linked here.
If you use rubber hose, make sure it is rated for oil and is capable of withstanding over 300ºF, as the oil will be hot exiting the turbo and it lives below the exhaust.
As a general word of advice – do NOT skimp on the oil supply and return system.
What do I need to build my own system?
The core components needed are shown below. This is bare minimum to make the car work. This should allow you to have a low boost setup capable of 5-7psi
•Turbo
•Manifold or adapter
•Wastegate (unless using turbo with internal gate)
•Charge pipes
•Couplers – rubber is cheapest
•Clamps
•Oil feed and return
•Downpipe
•FMU
What is recommended:
•Intercooler (water-to-air or air-to-air)
•Fuel Pump
•Silicone Couplers
•Quality T-bolt clamps
•Boost controller
•Larger fuel injectors (30+lb/hr)
•Chip for stock DME or Full Standalone
What do I do for fuel management?
All turbo cars require some sort of fuel enrichment. Without it you will make melted paperweights that make good conversation pieces. The bare minimum here is a Fuel Management Unit or FMU. It is my opinion that the BEGi/Cartech units are the best on the market. The BEGi 2025 works well and can be found at
http://www.bellengineering.net/index.php
The FMU causes a boost dependent rise in fuel pressure to force addition fuel through the injectors. This coupled with larger than stock injectors, an adjusted air flow meter (AFM) and a turbo chip (used for ignition timing retard) should safely allow 12-13 psi. An upgraded fuel pump is highly recommended when using an FMU as the dramatic increase in fuel pressure can tax the stock fuel pump
While the above solution will work well, many want the ultimate in control. Enter standalone engine management. While there are many brands of aftermarket standalones, it seems the most popular is the DIY unit Megasquirt. There are a good number of well tuned, fast turbo e28s using Megasquirt so there is an established community that is typically very willing to help out new users.
What size fuel injectors do I use?
Typically you will want to upgrade the injectors to a minimum of 24lb/hr when using an FMU. 30lb/hr is a very common injector size when using an FMU. RC Engineering has a simple calculator that will help you select an injector to suit your desired power level. For all M30 powered cars using the stock DME you will want to purchase high impedence, or saturated injectors. These typically have a coil resistance of 11-13 ohms. The use of low impedence, or peak and hold injectors will sink too much current from the stock injector dirvers and burn them out. High impedence injectors can be substituted for low, just not the other way around. Using high impedence injectors also makes the tuning of a standalone easier. The downside of high imp. injectors is that when they are very large (say over 72lb/hr) they can be very difficult to tune at very low pulse widths thus making idle tuning difficult.
Do I have to upgrade my fuel pump?
The short answer is no. The stock Bosch pump in good shape should be sufficient to supply fuel to a low boost setup. I say this with reservations however, as a fuel pump that cannot supply enough fuel will cause you to run lean and potentially kill your engine. Most stock pumps are at best 20 years old and things that get old aren’t what they were when they were new. A Walbro 225lph pump or a TRE Performance 255LPH pump easily replace the in-tank pump and will support well over 400whp. For around $100 it seems almost a no-brainer.
What spark plugs should I use?
It is recommended that when turbocharging that you drop two to three heat ranges on your plugs. NGK and Denso make plugs which work well in turbo applications. I run
NGK BPR7ES which well and are 2 ranges colder than stock. BPR8ES also work well and are 3 ranges colder than stock and work well for higher boost levels. NGK’s numbering system has the heat range decreasing (ie – colder) as the number increases, so the 8 is colder than the 7 (stock is a 5). I gap mine to 0.028” and have no problems with spark blowout. Also keep in mind that heat ranges between brands may not correlate directly.
I have more information forthcoming and will update this FAQ accordingly.
Enjoy!!
