This project has been in the back of mind for a few years now, and at the end of last summer I pulled the trigger and started to collect all the necessary bits and pieces to build a solid E30 M20B25 turbo. With so much documentation and experience out there it wasn’t that difficult to figure out what I wanted and how to get it. I want this write-up to be an overview of the whole project, and I’ll describe what I think are important points. If there are any questions, just ask! This is my first attempt at a turbo, so there were definitely some good learning experiences here for me.
The victim for this undertaking is an ’86 325, with an existing M20B25 swap and CatCam 283 (which was installed a few years ago).
The goals of this project are:
- ~300+ whp
- ~1 bar boost
- Driveable through town
- Easily serviceable
- Reliable (?)
- Less than $3000 (total)
This car is a secondary vehicle, so I was able to pull it off the road and have it in a non-running state for as long as necessary.
Let’s start off with an overview of the components:
- Holset HX35w turbo
- Megasquirt 2 + extra
- 42lb Lucas injectors
- Homebuilt turbo manifold adapter
- Homebuilt full 3” mandrel-bent exhaust
- 25x12x3” Ebay intercooler + plumbing (2.5”)
- Tial 38mm wastegate
- Single Magnaflow muffler
- Dual Bosch diverter valves
- ARP head studs, stock cylinder head gasket
- Homebuilt MBC
The poor, unsuspecting bronzit:
Since a major factor with this project is cost, the obvious answer for engine management is a Megasquirt ECU. I decided to go with the MSII with the extra code to have the “best-of-the-worst” hardware/software to work with. They are pretty straight-forward to assemble and use. Patience is important to reduce the amount of debugging you’ll need to go through in the likely event that problems arise.
Starting with the assembly of the MS:
Assembled MS with auxiliary Glen’s Garage pwm/ignition board
Modifications to the stock wiring harness:
The injectors are 42lb/hr, made by Lucas/Delphi. They are a standard size, so they fit into the stock manifold and fuel rail, with the same connectors.
42lb Lucas/Delphi injectors:
The ARP studs were another easy choice, being the most widely used and reasonably priced. The head gasket was replaced not too long ago, so I trusted it and didn’t want to go through the additional hassle of pulling the head to install the studs. I’ve heard of several people using the stock gasket without issues, so this was what I decided to go with. I loosened off all the stock bolts gradually and evenly, and then pulled them one by one and replaced them with the studs, then followed the torque spec for installation.
Installed without removing the head and using the stock gasket:
Beginning of the turbo manifold adapter. I bought an extra set of stock manifolds so I could use two of the same (seemed to be easier plumbing). The material is SCH40 mild steel (heavy as hell). I made all of the flanges myself to help minimize costs. The manifold only required a total of 4 bends and some straight section. It’s a fully divided manifold to mate up to the T3 flange I made.
Preliminary mock-up of manifold:
Seems to be a pretty straight shot: