Best Route to Turbo my M20?

[Das_Booooost]

I currently have a 1990 325i with an M20 that's down on power. It's still drivable and it has never left me stranded but I know it needs a rebuild pretty bad. This is not my daily so the time frame of this build isn't necessarily a factor but of course I don't want to be one of those people that has a car taken down as a project for years. I picked up the car for $700 about 2 years ago after it was left under a tree in Texas for nearly a decade. Needless to say it didn't run and needed some serious TLC. Currently I have regasketed everything outside of the head gasket, acid washed the fuel tank as the old fuel in the tank in there had varnished. Gutted the interior and cleaned it (still need to repair the dash). I've replaced the entire ignition system, had the injectors cleaned and bench tested, new filters, new fuel pump, among some other odds and ends. I got all that done relatively quickly once I took possession of the car and it's been left as is since. I drive it locally about once a week. But I think now is the time to finally get into the dirt and grime and get this puppy going for real.

I've never torn down and rebuilt a car engine, I do however rebuild jet engines for a living so I'm mechanically savvy. I know this is something I can handle, just need guidance. Like anything, the first time you do something is always nerve wracking. Price, whether we all like to admit it or not, is always a factor. I'm not one to cheap out and cut corners, but at the same time if I don't have to do something or it's not something that I might as well do while I'm in there, I don't want to spend the money to do it.

When i initially took possession of the car cylinder 4 had low compression, so I'd imagine its time for new seals and rings. Beyond that I don't know what I'll uncover once it's taken apart.

So the question is, what is the most financially responsible way to turbo build this ol M20 of mine? What certainly needs upgraded or replaced for this? What about tuning methods? My overall request is for someone, or a collection of someones to break this down for a newb. Feel free to provide links to parts and other build sheets, pics, etc.

I'm not picky about the power, but of course I want her to scoot. I don't need a big turbo setup, its not a racecar. Just a project, and something I'll drive around in and take to shows and such.

[mikey.antonakakis]

My input, might be missing some things, and of course it's up to you to determine cost/benefit ratio that you can live with. First the "do it at least kind of right" version, will be a couple grand most likely:

1. Get engine out, torn down, and clean everything so you can see what condition it's in.
2. Assess condition of parts, get a Bentley Manual or some other reference to give you specs/tolerances on everything. You'll need micrometers, dial bore gauge, etc. Plan to replace anything out of spec that can't be machined to a new spec (e.g. if bore is not great than you probably want overbore with new pistons).
3. Probably plan/budget to have for head:
   1. Head decked, maybe cut valve seats and lap valves, stock valve size. You can make plenty of power with stock size valves.
      1. You can do this yourself with proper tool for the job, but it's kind of a "cut then measure" job so would be helpful to have someone experienced do it if you can.
   2. Try to reuse old valves, but it may be more trouble than that's worth if they are really messy. Lap to the new seats either way.
   3. New rockers, eccentrics, hardware. Not totally necessary depending on their condition, but a good idea if budget allows.
   4. Don't necessarily need new valve springs, I think the manual has a spec on them.
   5. There are other areas of the head (cam journals for example) that may be more than trivial to DIY if out of spec.
   6. ARP head studs if turbo.
   7. Stock head gasket can hold lots of power if tuning is good, Goetz or OE I think are the best for stock style. No need for MLS.
   8. New valve stem seals.
   9. Check valve guides for wear, replace if needed.
   10. Other gaskets/seals/rubber inserts, etc.
4. For bottom end:
   1. Freshen up the deck, bore out if cylinder walls are trashed (then you need new pistons)
   2. If bores are good, you may be able to reuse the old pistons. If pistons are out of spec you need new ones or good used ones.
   3. Definitely rings.
   4. May be able to get away with just flex-hone for the bores if it measures in spec with a little room to spare.
   5. Probably plan for new bearings all around unless the old ones are flawless. Need to measure bearing clearance, plastigage works for this and is cheap. May need to buy size-adjusted bearings.
   6. New hardware. Stock is fine if you're keeping redline reasonable.
   7. New oil pump is a good idea
   8. Gaskets, seals, etc.
   9. Good assembly lube.
   10. Timing belt and water pump.

Obviously that's a lot of work and a lot of money. The quick and dirty route, maybe $500(??), I haven't checked prices:

1. Disassemble and make sure nothing is totally FUBAR
2. Ball hone the bores
3. New rings
4. Clean up the valves and re-lap if they're super gunked up.
5. Gaskets
6. Freshen up deck and head surfaces.
7. New bottom end hardware
8. Turbo

Worst case with second option is you really destroy something. But if the engine was in decent shape, it's unlikely to grenade with a cheap approach to a rebuild. Much more likely to go catastrophically wrong for some other reason, like bad tuning, out-of-control boost, etc. Problems that will still kill a really well-built engine.

First few posts of my build thread has basically both versions for the various stages of life the car's gone through in my hands. First version was super cheap broke college student approach, spent as little as possible. Despite running the engine essentially without oil for several heat cycles do to oil filter sandwich plate issues, the car ran for probably 10k miles with moderate boost (~10psi) before it spun a bearing. Thread also has info on cheap turbo setup requirements. I'd recommend MS2, more than enough for basic turbo setup, maybe a plug-and-play if those are still available since your car is a late model.

I should also add that you can probably still find cheap used M20s - maybe not as easily as you used to (the engine that donated its head to my car's current iteration was purchased for like $150 as full long block + transmission circa 2014). Kind of nice to build the engine not already in your car so you can drive in the meantime.

[varg]

Pretty comprehensive. Price wise if there really is something wrong with the engine itself it's still cheaper to buy a known good used engine than to rebuild, since the machine work alone costs more than a good used engine. Yours could have low compression for many reasons, valves, rings, head gasket. If there is any evidence of it being overheated, like a blown head gasket, get the head checked for cracks. M20s don't like to be overheated. Nothing really needs to be upgraded aside from the fuel system, clutch and head studs to safely turbo a good M20, there's just a lot that needs to be added to the car. You don't even need to upgrade the ignition system for a mild build.

[hozzziii]

*scribbling notes furiously*

[It's Soda Not Pop]

Bang for your buck would be to just do a oem refresh of the engine. Seals, rings, bearings, resurfacing, gaskets. Then find you a good turbo kit or find a kit and buy stuff based off that kit. A guy there is near me had very clean "is" with a basic oem rebuild and a Kamotors budget brawler turbo kit. 13 lbs of boost and he walked most cars on the road (including some cocky ass mustang guys). Nothing fancy unless thats what you want.

https://www.7speedshop.com/products/kamotors-budget-brawler-bmw-e30-325i-turbo-kit

[4ce30]

I’d run the kangaroo cast manifold.
megasquirt plug and play ecu.
atleast 36lb injectors.
stock fuel pump and fuel system fine for a while.
borg Warner s252,s257/precision 5858, 6060
or holsets he351, he341, hx35, hy35
ebay intercooler fine
stock oil cooler fine
plenty base start up tunes available on diyautotune
gonna need some sort of clutch setup stock maybe 6psi

[Das_Booooost]

Thanks for the input everyone. So far I've gotten the engine almost 100% torn down. My next step is machine work. And here's where another question arises.

What all will a machine shop do? I know they can deck the surfaces of the head and block and hone cylinder walls, but what else? Do I need to take it to them completely dismantled, such as crank out, rods/pistons out, etc?

I'm new to all this and taking it step by step, so excuse my ignorance. Trying to learn as I go.

[95BMWIC]

Im the one that sent you here - This forum has a much deeper knowledge pool than the other forum (and more active).

Post some pics of the build when you decide to go..

[digger]

Thanks for the input everyone. So far I've gotten the engine almost 100% torn down. My next step is machine work. And here's where another question arises.

What all will a machine shop do? I know they can deck the surfaces of the head and block and hone cylinder walls, but what else? Do I need to take it to them completely dismantled, such as crank out, rods/pistons out, etc?

I'm new to all this and taking it step by step, so excuse my ignorance. Trying to learn as I go.

they will do what you ask. They will clean it (don't hot tank intermediate shaft brgs), if you ask them they can check all crank journals (mains and big ends) check all brg clearances, adjust piston ring gaps and install rings, install pistons to rods and and assemble the short block if you want. Lots of other things to like line honing, resize rods etc etc (if/as required)