BMW 2002 Turbo Conversion
The BMW 2002 is a great little car. Light, nimble but a bit under-powered. I am not looking for a drag racer but would like some on-demand power for passing slowpokes on the highway. My 1974 was originally ~105HP but likely less 40 years later. I could build up a high revving, individual throttle body screamer (and may still) but I have always wanted to try a turbo car.
Personally, I hate carbs and the first thing I did after rust remediation was replace the carbs with an E21 manifold and Megasquirt EFI. This is reasonably straight forward and covered elsewhere. However, it did provide me with a good base for adding a turbo.
What follows is a summary of my turbo conversion. I try to address the major decisions and issues but it is not a step-by-step guide.
For a good primer into turbo basics, check out the following site. It was written for Civics/ Integras but has some great explanations and definitions.
http://www.beesandgoats.com/boostfaq/g2icturbo.html
Turbo
First things, first. You need to decide what turbo you want to install. There are online calculators, books, forums, etc. that can point you in the right direction. An excerpt from my calculations with a couple turbo maps is shown below but the easy route is to pick a similar size car/ engine that has a lot of turbo support and see what they chose and why. For the 2L M10 engine, this will lead you to a GT2860 (“Disco Potato” in the SR20DET world), a T3-Super 60 or even a junkyard turbo. All are viable choices. I chose the GT2860 but, if I were to do it over, I would look hard at the T3 as the manifolds are all T3 flange and it gives you room for future growth.
Turbo Manifold
It is challenging to find a manifold that fits with the least amount of compromises. There are two available new from Ebay, some E21 manifolds occasionally available on the forums and, very rare, the BMW 2002 Turbo OEM manifold. I finally settled on the smaller top mount Ebay offering. It has decent clearance to the thermostat, chain tensioner, front engine bay and can be bolted to the head without short studs or modified tubing. In order of my install attempts:
E21 bottom mount:
Pro: Bottom mount is cleaner looking and potentially has less need for support. With a T25/T28 turbo, it clears the steering idler and engine supports. The oil drain routing will be challenging.
Con: No room for the downpipe. There was only an inch or two to the passenger footwell.
Ebay #1 (Boost Brothers style):
Pro: Cheap and readily available. Closest to equal length tubes.
Con: Big cantilever requiring support/ brace. Puts the turbo very far forward requiring more cutting in the nose and potentially interfering with the thermostat and chain tensioner. Sharp bends at cylinder #1 & #2 requires short studs and/ or massaging of the tubes to allow bolting to the head. Requires T25-T3 adapter for small turbos.
Ebay #2 (my current install):
Pro: Best fitting manifold, reasonably priced.
Con: Requires support/ brace. Unequal tubes. Need short studs at turbo flange. Need T25/T3 adapter for smaller turbos (use the thin adapter!).
I added a brace from the bottom of the manifold flange to the block. The brace also supports the drain line away from the frame rail.
The top mount Ebay manifolds have a T3 flange. If you want to use a T25/ T28 turbo, you will need an adapter. There are several cheaper but taller ones available on Ebay but they will not give the required clearance to the fender. You will need one of the thin adapters (I was able to use the cheaper Mamba 1-piece).
Note: Although the current manifold is working well and provides a fairly easy solution for anyone wanting to turbo their 2002, I still like the OEM solution of a bottom mount turbo. If I ever get the time (and talent), I will look into fabricating a custom bottom-mount manifold.
Intercooler/ Charge Piping
Intercoolers will help keep your intake air temps down to increase power and provide margin to knock. Finding an IC of appropriate size and a place to put it is the challenge. I used a generic 7×20 IC in front of the radiator. The small elbow supports were removed and the IC is supported from the top plate with M8x80mm bolts and some PVC spacers (to make the pipe routing a bit simpler).
Silicone hoses used:
- 1x 2”-2.5” elbow (turbo compressor outlet)
- 1x 2.5” elbow (IC inlet)
- 1x 2.5” 135deg elbow (IC outlet)
- 1x 2.25-2.5” elbow (TB inlet)
If the silicone hoses don’t hold up, I will replace with some tight-radius aluminum bends.
For the charge air pipe between the intercooler and throttle body, I added a Blow-off Valve (BOV) flange (2” Tial style) and Intake Air Temperature (IAT) bung (1/4” NPT for GM sensor). I failed at TIG welding these so went with Alumaweld (AL Brazing/ Soldering) instead. The beads on the cut ends were hand formed using modified harbor freight crimping pliers.
Oil/ Water Lines
Your selected turbo may not have the water-cooling option but mine did. Working out the oil & water connections, routing, line sizes, adapters, etc was the greatest source of aggravation for me. My current arrangement:
I purchased most of the fittings (Russell Brand) and hoses from Amazon, Summit Racing and Ebay.
The oil feed line has some extras fittings as I failed at building an AN4 line. So, I bought an Ebay generic 4AN line and some adapters/ unions.
Note that taper fittings (NPT) need teflon tape or plumbers putty to seal. This will prevent many leaks on startup.
Oil Cooler
An oil cooler is recommended as turbos add quite a bit of heat to the oil system. I purchased a cheap 10-row cooler but could not figure out a clean location that would put the fittings on top (no air bubbles) and leave room for an electric pusher fan in front (if needed). Before the turbo install, I had run a Volvo 240 radiator which worked well and included a transmission cooler. I reinstalled it and plumbed this up using an oil filter sandwich with thermostat and oil temperature sensor. If it gets too hot, I will figure out some way to add the separate cooler.
Update 1: The oil temperature was staying reasonable but those AN-6 fittings to the Volvo oil cooler were too small. They choked flow once the thermostat opened and my oil pressures suffered. For now, I am running without an oil cooler but will look at installing the 10-row.
Update 2: Even with no oil cooler, my temps were good but the oil pressure was still poor so I dropped the pan and checked the oil pump. It was in bad shape so I replaced it. Oil pressures are good now and the temperature (monitored from the pan drain is good so no oil cooler for now..
As described above, I had issues with oil pressure (due to a bad pump) and questionable connections to and use of the volvo radiator oil cooler. When I had the pan removed to replace the pump, I rerouted the turbo oil drain to the front of the pan like the OEM Turbos and put a temperature sensor in the drain plug. I am monitoring pressures and temperatures with a couple VDO gauges in the center console and all has been good for the last few months during a Houston summer.
Downpipe/ Exhaust
The exhaust was fairly straightforward using a 2.5” V-band clamp at the turbo. I had a local shop make up the rest of the 2.5” exhaust but added a flange/ joint at the transmission to make the downpipe (and turbo) removable for access to the spark plugs.
Note: I started getting some backfiring on coast and closed throttle, usually signifying an exhaust leak. I checked and found loose bolts at the manifold to turbo connection and at the turbo to downpipe connection. I tried retorquing but they backed off again after a couple heat cycles. Some google searching found a possible solution: Nord-lock washers. I ordered up a set from Amazon, installed and torqued per the instructions and have had no issues since. Success!
BOV/ Wastegate/ Boost Control
This has been covered above but you will need a wastegate to limit boost, a blow off valve to release pressure on throttle closing and, potentially, a means to monitor and control boost. Monitoring is done on my setup using the Megasquirt EFI and boost control is limited to the wastegate. I also have a Turbosmart manual boost controller but haven’t installed it yet.
Vacuum lines
On the original EFI conversion, I pulled manifold vacuum from the 1/8 nipple near the throttle body to feed the fuel pressure regulator and the MAP signal to the ECU. For the turbo, I also needed manifold pressure to the BOV and Wastegate. I just used some tees but plan to replace with a nice Ebay vacuum manifold.
Fuel/ Spark/ AFR Control
As mentioned previously, my AFR monitoring, fueling, spark control, etc. is all handled by the Megasquirt EFI. For the turbo conversion, I swapped the 19# injectors for some 36#, added boost bins to the AFR, fuel and spark maps, included ignition retard under boost (1 deg/ pound) and added an overboost fuel cut similar to the rpm limit fuel cut.
OEM spark plugs are roughly equivalent to NGK BP5ES. I am running BPR6ES (resistor to minimize interference and a bit cooler for margin to knock).
The spark plug wires are an Accel universal 8mm set with fiberglass sleeves to help protect against the turbo heat.
For additional heat protection, I added a turbo blanket. However, the first few drives really heated up the tunnel and passenger floorboards so I added a double layer of heat wrap to the downpipe.
The turbo blanket and header wrap dropped temps in the engine bay and, more importantly, transmitted to the passenger compartment. However, I felt that the passenger floor was still heating up a bit too much so I pounded the firewall to provide a bit more clearance and am investigating an exhaust shield or blanket. Updates to follow.