M30B28 EXPERIMENTING with DYNO PROOF - Overboring/Motronic conversion/manifold changes and more..

[RobertRO]

If you still consider a setup of late B30 (E32/E34) pistons with an 80mm crankshaft, there's right now an ad in Netherlands for a (new?) set of very rare 9.2:1 pistons for stock 89mm bore.
Note that the stated compression ratio is calculated for the late B30 cylinder head. If you use an earlier head, make sure you do your due dilligence.

https://www.ebay-kleinanzeigen.de/s-anz ... 6-223-1309

No affiliation.

[Tibo]

It's been a while since the last time i posted here so here's an update!

I finally managed to find a set of pistons locally, they are from a b32. This means i'll be building a 3.2 liter instead of the 3 liter. This also means i have to use an 86mm crank instead of the 80mm i had prepared. I have one from a 3.4 liter block so i dissassembled it and brought it to the machine shop to get checked and polished.

I am still waiting on the crank now, should have it by the end of the month.

I had the pistons and the throttle body sodablasted so they are ready to go.

[Shawn D.]

Are you going to get the piston tops treated? Otherwise, those are quite rough, which could lead to preignition due to hot spots.

[Panici]

Are you going to get the piston tops treated? Otherwise, those are quite rough, which could lead to preignition due to hot spots.

I was thinking the same thing, those look ROUGH.

What kind of treatment would fix this?

[Shawn D.]

Are you going to get the piston tops treated? Otherwise, those are quite rough, which could lead to preignition due to hot spots.

I was thinking the same thing, those look ROUGH.

What kind of treatment would fix this?

I'm not familiar enough to know, but the places that do such treatments would.

[Mike W.]

I can't say I like the looks of those pistons, the porosity does bother me, and I haven't seen it before.

But... These are used pistons, right? They've run like that before, likely a long time. And the top will carbon up more than likely, so I don't think it will be a problem, I really don't. I actually tell people who are rebuilding engines not to bother with the tops of the pistons. I suspect I'm universally ignored, but carbon on top of the piston won't hurt anything and will reform shortly if you do clean it off. So I wouldn't worry about it.

A little late now, but rebuilding engines about all I do is decarbon the ring grooves and maybe rinse the pistons in solvent or wipe them off. They might be at the factory, but it doesn't have to be white room clean. A couple of things like bearings and crank journals need to be perfectly clean, but for the most part, no, it's not needed.

Coatings? I can't say it's a bad thing at all, but probably unneeded.

[Jobi]

A bit of a dig out but I might follow the same path and go for B30 pistons in my euro b28.
I’ll go for E32 pistons.

Are you guys sure about the compression ratio it would give? I’ve read 9.8 which sounds quite perfect imho.

[Mike W.]

A bit of a dig out but I might follow the same path and go for B30 pistons in my euro b28.
I’ll go for E32 pistons.

Are you guys sure about the compression ratio it would give? I’ve read 9.8 which sounds quite perfect imho.

First you need to clarify, 3.0 pistons or 3.3 pistons? And what crank, an 80MM throw as a 2.8/3.0 would have? 3.3 (3.2 really) pistons with a 3.0 crank will give you lower compression, not higher. 3.3 pistons, (again, US terminology) are designed for a longer throw crank. It's not quite this way, but lets assume all the pistons are flat top. 2.8/3.0 pistons will come up to the top of the block. But with 3.3 pistons designed for an 86MM throw crank they will be 3MM below the top of the block. They were designed to come up to the top of the block with a longer throw crank, so a shorter throw crank, an 80 as in a 2.8/3.0 they will be short and very low compression.

It doesn't cover a lot of the euro displacements, but you can probably get it to work with a little tinkering, but here's a calculator, https://www.mye28.com/viewtopic.php?t=51939

[Jobi]

I’m talking euro b28 crank with 80mm throw and euro E34/E32 89mm pistons with a kind of a dome on top of them (same pistons as pictured above).
Block would be rebored b28 block and head is std m30b28.

[Mike W.]

I’m talking euro b28 crank with 80mm throw and euro E34/E32 89mm pistons with a kind of a dome on top of them (same pistons as pictured above).
Block would be rebored b28 block and head is std m30b28.

You should be able to overbore to 89MM, but you would need 3.0 pistons, not 3.2 pistons. Now if you are going to use E32/E34 3.0 pistons it would probably work and give you higher compression. I'm aware of the late 3.0 engine, but since we didn't get it here I don't know a whole lot about it. You may or may not have interference issues, do a mock up before assembly to test for clearance as early and late heads have a different combustion chamber shape. I think the late 3.0 engines were 9:1 compression, and making assumptions based on the 3.5 engine we did get, I doubt you would get 9.8:1 compression. My guess is it would be more like 9.3 or 9.5:1. That's a slightly educated guess, not a statement.

On boring it out keep this in mind, 2.8 engines had freestanding cylinder liners, 3.0 engines had siamesed cylinders. I think it will still work, I've personally done 89 to 92MM without problems, but it was thin.

[Tibo]

Hi everyone,

time for a very very long overdue update on this subject.

At the end of 2022 i very unexpectedly was given the opportunity to take over the business where i had been working for three years as a mechanic. I decided to go for it and so this has pretty much taken all the time i have had over the past two years. I did not only take it over, i also moved the business. I'm now the owner for about a year and a half and things are starting to fall into place Which means i can start thinking about doing some other stuff again, like this engine project. For who it might interest, the business is called 'Munich Icons'. Lots of beautyfull classic bmw's on our IG and FB

Anyway; back to the engine project.

I did find a little bit of time to put together the bottom end.







And another pic of the car in question (pic taken over a year ago)



Engine out



And this is how it currently sits. And has been sitting for about a full year..



But that's enough about the car. I might make a seperate thread for the entire build at some point.

I then discovered that the head i prepaired is actually not usable. I forgot to check the condition of the camshaft journals before sending it off to get prepped. They are very worn and beyond use.

[adam_poll]

Aw, I've been following you for a while on instagram, lots of very nice cars coming out of your shop.