Learn me: budget performance bottom end work

The M30B34 straight six in my E28 is in need of a performance boost. It doesn't leak or burn anything and doesn't smoke, but 180HP from a 3.4L straight six is a bit sad. I don't plan on going turbo but I would like to get more power out of this thing, and the best way to do that without swapping engines or going FI is to either add the Euro-spec 10:1 pistons, or swap to an M30B35 head and 9:1 pistons. These are relatively available and reasonably priced compared to other options.

Now, I've never done bottom end work on a car engine before. I've done a ton of work over the years but somehow never tackled this level of engine work. The guys on the BMW forums say that if you go in there you better be prepared to spend $3000 or you did it wrong, which sounds silly to me. Or maybe I'm just naive...

How do guys do Challenge engine builds on the cheap? Just how paranoid do I need to be about stuff like rotating assembly balance, honing cylinders, etc? Where does the line between "better do it while you're in there" and "really not necessary on a healthy engine" get crossed? I don't want to build an exotic forged-internal race engine, I just want to use the right combo of factory parts to gain some reliable power and maybe learn a thing or two in the process.

So is this a pipe dream? Are the BMW forum guys right in that it's really not cost effective, or are they just not DIY-savvy? As a complete noob to any engine work more advanced than cylinder head removal, what do I need to know? How far would you go?

Challenge guys do challenge motors on the cheap, or don't use fancy German garbage. Challenge engine only need to hold up for one drag, and one cone killing. Otherwise, said challenge guy is using a SBC.

From what I've seen/read the trick to bottom ends is to either spend cubic dollars or keep the revs down around stock on carefully inspected stock parts (But do address any known weak links that definitely aren't just internet lore). They can usually handle the increased cylinder pressure, the forces of revving it higher than designed is what tends to break stuff.

Trackmouse wrote: Challenge guys do challenge motors on the cheap, or don't use fancy German garbage. Challenge engine only need to hold up for one drag, and one cone killing. Otherwise, said challenge guy is using a SBC.

Thanks for that. I actually quite like my "fancy German garbage," as if a massive single-cam, iron block straight six is really otherworldly...

BrokenYugo wrote: From what I've seen/read the trick to bottom ends is to either spend cubic dollars or keep the revs down around stock on carefully inspected stock parts (But do address any known weak links that definitely aren't just internet lore). They can usually handle the increased cylinder pressure, the forces of revving it higher than designed is what tends to break stuff.

This car will see some track time and I was thinking of going to the lighter flywheel from an earlier model...I mean, wouldn't I (theoretically) have similar risks on a 150k mile replacement engine from another car? That being said this is a big 'ol six, I don't plan on revving it to the moon.

My dilemma is whether or not it's better to wait for a used B35 to show up, throw it in with some bolt-ons and say "good enough" while hoping it holds together or tearing into my current B34 a bit. Having never journeyed into bottom-end work before I really have no idea how far down the slippery slope I might fall...

Buy that salvage M5 in the other thread and swap it.

You've got the 'big six,' in what was the fastest production sedan in the world in '85. What more do you want!?

Seriously through, an engine swap is the cheaper route to power vs modding what you have. M54B30?

In reply to Tyler H:

I don't like the new-gen engines as much and they are far from a bolt-in swap. If I were to go that route S52 would be the answer, but...this is a genuine grey-market Euro car in pretty nice shape, and I've already scored some pretty cool period bolt-ons for it. 230HP is relatively easy from a B35 with upgraded engine management and bolt-ons and that's a number I would be happy with.

This whole thing started by realizing that sourcing the revised pistons and head for a B35 conversion would be easier than finding a B35 locally so I figured I'd ask.

m30 engines were known for having bulletproof bottom ends - easy button = add turbo 9-10 psi = 300+ hp without opening it up. 292 cam, MAF conversion, intake and headers will get you over the 200 mark. More involved - add s38 head to m30 block - should result in something similar to m1 or m5 hp - closing in on 300 hp (1980-1982 there was a bmw 745i with an m102 engine - factory turbo m30 - 245 hp or find crashed and rusty e34 m5 = 315-330hp). Takes some modifications for oil and coolant passages for an s38 head conversion - it is documented how to do it with hand tools. There are also stroker kits out there or was - the crankshafts are expensive. Most of the engine failures on m30s involve oiling issues at the head - an oil feed line gets loose and starves the head.

In reply to oldtin:

This is my third M30 car and I spend a lot of time in MyE28 so I've read the recipes.

I do want to stay naturally aspirated on this build. Unfortunately dyno plots don't really back up any more than 190HP on the US 8:1 motor regardless of bolt-ones which is why I'd like to start with a B35. Already have a trick set of Supersprint M30 headers, the desirable 265/6 transmission, trying to source a Paul Burke cam etc so really it just comes down to solving the depressingly low US-spec compression issue, whether that's through internal swapping or just putting in a B35.

S38 head/swap, TCD turbo, etc would cost more than I paid for the car...though that would be nice!

A set of entry level Fowler mics on Amazon right now for $105. Fowler bore gauge set $109. Harbor Freight digital indicator and stand $65 (indicator fits right into the bore gauge for an added bonus) Buy whatever engine building/blueprinting book is cheap on Amazon this week and a copy of the shop manual for whatever your building.

The fact of the matter is most of the time if you're putting production parts in a production engine that hasn't had a serious failure everything is within spec but it's best to have it on paper.

If you find some bore nastiness most engine machine shops will do a proper hone (not involving a DeWalt drill or ATF) for less than $100. The "secret" to cheap engine work is knowing where to spend money. Crank polishing is usually pretty cheap. Get good and comfortable with gaping rings. Garage sale lawn mowers are great for learning the ins and outs before moving to your actual project.

The "secret" to cheap engine work is knowing where to spend money.

Well put.

I've done a lot of mostly-used-parts 'rebuilds' in my day and as mentioned, most of what's in a bottom end is usually just fine. I agree with the suggestion of buying measuring equipment rather than throwing money at replacement parts when you don't know what needs to be replaced. Even bearings are not a given as if you're putting them on an out of round surface you still might have put your money in the wrong place. As far as durability goes, you'd be surprised the extent to which 'looseness' gives you survivability/margin for error. I've NEVER experienced a truly negative consequence of piston to wall clearance and ring gaps that i thought i made too big have worked out great. That's more relevant to turbo builds, but it goes back to what i was saying about used parts usually being just fine, sometimes even if 'out of spec'.

The street stock class at my local track is for 350 cubic Chev v8's. Two barrel carb, stock cast manifolds,flat top pistons, no internal mods, stock rods etc...

But knowing the cars and teams, I am sure there is a 50 to 75 HP difference between the fast cars and the slow cars. I can hear the difference just walking past the cars. My point being that there is an incredible amount of power to be found by building an engine properly, even if it is visually identical to a slower one.

sounds like you've got it narrowed down to rebuild vs. engine swap. At least with a rebuild you know what you've got.

Thank you guys! This is starting to sound much more achievable. The hurdle I was coming across is the amount of machine work everyone assumes you need, but it sounds like you can do well without just throwing money away if it's spent effectively.

I'm thinking the route I may go will be to just install the Euro-spec 10:1 pistons and run the head I have with a hotter cam. It sounds like if I do that, I should have the machine shop look into:

• Crank polish
• Balance rotating assembly (to be safe?)
• Good hone if bores are questionable

After that, just measure everything real well and replace bearings/rings as needed while putting it back together...

i don't recommend this, but back in my vw days of the mid to late 90s, we used to stack headgaskets on ABA motors to lower the compression and prior to bossting as an alternative to building the bottom end.

captdownshift wrote: i don't recommend this, but back in my vw days of the mid to late 90s, we used to stack headgaskets on ABA motors to lower the compression and prior to bossting as an alternative to building the bottom end.

On any engine that starts out with decent piston to head distance (quench), this will actually make it more detonation-prone, not less (unless you drop the compression by a metric crap ton).

The secret to a budget bottom end is to use a core that doesn't need a bunch of machine work and then don't do any work that isn't necessary. It's really that simple. Starting with an engine that doesn't burn oil and carries good pressure is a great start. You won't know for sure what's needed till you tear it apart. Don't order any parts till it's apart and inspected.

Get the Pistons to bump compression. Remove head and oil pan, pop Pistons and rods out.

Take Pistons to machine shop and have the rods swapped over, add new rod bearings and bolt it back together. If the engine doesn't need a rebuild now don't rebuild it.

you can do the head, and it needs to be removed for your New Pistons, the engine is on a stand so when you turn it over Start taking picture's. with the pan off start Marking each rod and crank bearing cap AND what direction they need to be put back. before I owned A Stamp set/mine are letters not numbers/ I marked them with a Sharp chisel and a hammer, If the bearings are looking Good just put back New Of the Stock size,If it's not Scored the polish isn't needed,Plasti-gage is easy but like I said if nothing is damaged it's not needed.You Can do this if you can do the head, A GOOD Torque wrench is all you need. IF the bores need work the shop will tell you the size, Rings can be bought in a .005 over if needed, more than that will require pistons and rings. It is simple but doesn't always seem so.Don't buy pistons or bearings until you have looked inside.

If you don't belive me Just ask Pete Gossett Don't ask him about Carbs,Lol

Plastigauge is cheap and super convenient for measuring things like bearing tolerances. Also, make sure it's properly lubed on reassembly to ensure that its not dry for any amount of time.

I think you've got the right idea using the euro 10:1 pistons and an upgraded cam for a bit more fun at the top of the rev range. I think the minimum while you're in there work on an M30 would be to replace the plastic timing chain guides along with resealing everything. The only other caution would be the rocker arms depending on how aggressive the cam is that you end up with.

I've mulled this over myself, I dropped an NA spec M30B34 into my '84 525i (came with a M30B25, slow!) that I had and it's been a big improvement, when I want more it will either be turbo or drop in an M30B35.

For your flywheel you can just have the backside of your stock single mass one machined down to 12-15 lbs rather than hunting down a pre 01/84 build 533i or M5 flywheel. I actually have a 533i parts car with that flywheel in it but the $150 CAD I spent to have mine lightened sounded better than crawling around under it for a day to remove the transmission and still need to get it refinished (another $100 on top of the lightening here).

Good luck!

Adam

So if I'm changing pistons and not doing a hone, what's my best bet for rings? Re-use the old ones?

In reply to pointofdeparture: New rings for sure. Have the machine shop clean and "Ball Hone" the block. This will slightly scuff the cylinders so the new rings will seat. The biggest bang for your buck will be the cam swap. Can the ECU handel the new cam, or will it need adjustment?

pointofdeparture wrote: So if I'm changing pistons and not doing a hone, what's my best bet for rings? Re-use the old ones?

at the very least a bead hone and rings as you are likely to brake the old rings taking out the pistons.that is kinda normal because they don't want to pass the ridge that forms at the top of the bore.

In reply to f6sk:

You can absolutely DIY a dingleball job. They're even pretty cheap.