3 engines - M20B20, M20B25 and M52B28 what to do?

[Kieran_n22]

I was going to go on and do a M52 conversion and had everything for the conversion but then found out the head was cracked. This with a couple other reasons has made me think to build a stroker!

I'm a trainee mechanic and haven't ever built/rebuilt an engine as such the most I've done is a headgasket and a couple other bits but I have the passion to do this build!

I've read the wiki on the 2.8 and a couple threads and I need to do alot of research before I dive into anything because to be honest I have no clue about these compression ratios (yet). But can anybody maybe point me in the right direction on what first to do or maybe what build I could produce without going too crazy!

My 2.5 is an early one I think and it look like it's better to have the later one for the pistons - this engine is in the car at the moment my 2.0 is sitting in my garage in one piece and the 2.8 is in pieces everywhere lol.

Looking forward to some response or links.

Cheers, Kieran

[HairyScreech]

Ok, couple of things, firstly i gather you have looked at the wiki and been through some threads on here (otherwise you wouldn't have said you have the 3 engines etc)

Is the 2.8 single vanos or double vanos?
A single vanos is preferred as it makes things easier.

The only thing you want from the b20 is the conrods, which is a bit of a waste if its a good engine, if its a nice one then sell it and just get some 130mm rods.

The earlier high comp pistons will give ~10.3:1 or around 10.8:1 with the block skimmed correctly. (0.5mm)
Which really is good and a lot more lively than the 9.3 - 9.7 max you would be looking at with the low comp pistons.
The high comp pistons are harder to crop and need more taken off the skirt.

If you can do a head gasket and fit the engine then the rest of the build is pretty simple, just ask questions if your unsure and don't do anything unless your sure first.

If you get some pictures of the 2.8 up then i expect we can identify it from that.

You also have pm.

[steve_k]

gut the 320i block & rebore it to 84mm, fit the b28 crank with the spacer, fit the b25 pistons to the 320 130mm rods then onto the crank & rebuild he head & go for a m20b28 build.

thats about as much as i understand how the build goes

[Quaser]

buy yourself a m50b25 engine, you probably already have all the ancillaries of a m5x so just the head and block will do.

put the m52 crank in the m50 and make it into a 2.8 - now you have a steel blocked m52 as such - perfect to put arp bolts, mls headgasket and turbo it to 500bhp

personally, from what i can see - all the 2.8/2.7 builds that have come up on the zone, the proper 2.7's seem to make more power!

or - you could get a 2.7 bottom end and bolt the 320i head onto it and just put that in your car.

Thats what i'll be doing, so if you want to have some practice, feel free to come and do that on my car

[Kieran_n22]

Oh gheez all 3 of you are telling me a different theory lol.What power am I looking at with these applications? M50s weight too much plus I'm all about handling lol even though I have a convert. 2.7 bottom ends are hard to come by aren't they? I was thinking to buy another engine to work with as I don't wanna take my m20b25 of the car as it is in storage ATM. I'm swaying to the side of keeping it looking oe with a 12v in place. My m52 is single vanos I know the problems with double. So I only need to skim the block? Not pistons? Reboring the b20 seems a good idea as its out the car and sitting in my garage at work. Hmmmmmm

[Quaser]

i think we first need to know what your budget is

[Kedge]

I've just gone down the M20B28 route. Quaser is right in what he says, the 2.7s do seem to make better power but they are ones that have had a lot of time and money spent on them. Looking at all the 2.8 builds they've all really been homebuild jobs and people are still experimenting. Check out the Wiki page I've done with a load of dyno graphs - http://www.e30zone.net/e30zonewiki/inde ... yno_Graphs

Like you say, the parts for a good 2.7 are getting hard to come by now. If you're going to build it yourself I'd go M20B28 if your M52 crank is the correct one. I'm also going to be sticking with the early M20B25 pistons for the extra CR, for these you'll need to reduce the depth of the skirt to clear the crank, nothing has to be done to the tops, the facelift piston will clear the M52 crank without work though but give lower CR. Both require a block skim I think.

[Kieran_n22]

Hmmm ok
Well to be honest my budget wasn't ever thought about it but the budget of a partially built m52 and all bits to go with it is the answer so let's £500-£700.
What's the "depth of the skirt"?

[Quaser]

and what do you want out of the car? cruiser, drag racer, top end? economy? 0-60 times? etc

with m20's, you have most of the bits, if your going to make a stroker, then your budget will probably be used up on the mapping alone.

With m52, i think the going rate is about 2k if i recall correctly - with wiring looms, fans, exhaust manifolds, gearbox, prop shaft etc all need to be considered.

Im building a 525e/320i head/325i cam and inlet for mine - it has come to around £300 so far on parts - thats a 325i cam, inlet, throttle body, head gasket kit, bottom end etc and will probably get a speedtouch chip for it.

Like i said - if you fancy getting your hands dirty, your welcome to come and practice your engine building skills with me here.

Kaz

[Kieran_n22]

0-60 with equal lbs torque figures with bhp
Hmmm I know it begins to get pricey
I have some 2.4 Transit engines at my garage I can work on.
How much would a map roughly be?

[Quaser]

remaps can cost around £500 -

[Kieran_n22]

I thought of something around this figure

[Mikey_Boy]

Depth of skirt is piston skirt depth...

Have a look on the e30zone Wiki and read some of HairyScreeches threads for guidance - excellent stuff in both.

For simplicity, I would go for an M20B28 - a great way to learn how engines go together - really satisfying when its built and first starts - it's probably the cheapest option and an easy way of getting 200+hp and by far the easiest in terms of wiring etc.

Remap is around £500 as stated above.

Most importantly, take your time and make sure every step is right - when building engines, cleanliness is EVERYTHING. If you are a trainee mechanic, this is great way to learn loads!

Good luck whatever you decide, but a fresh built M20B28 would get my vote...

[Gunni]

Put the B28 in as it is. More low end, more high end, better fuel economy

[HairyScreech]

^^ fully agree with gunni, however i think the point is the m52 is scrap, cracked head and probly other issues that come with overheated m52s.

I dont quite understand where the myth that 2.7s make better power than the 2.8s has come from, a quick glance through the graphs that kedge posted to see that there is not a lot in it.
The difference seems to come down to a well built/shop built high comp 2.7 makes better power than a home built 2.8 with low comp pistons. That's hardly a sign there is anything wrong with a 2.8.
Add that to the fact that a lot of 2.7 blocks/cranks are now worn out scrap and are well past there best and there is a plentiful supply of 2.8 cranks then its easy to see why the 2.8 is the way to go for a home build.

An m5x powered e30 is a very capable tool, however they are not the same to drive as an m20, they make power in different places and the feel and sound is different.
Pretty much if you want a 2.8 m20 then build a 2.8 m20, if you want something different and similar in speed then put an m5x in.
If speed is all that matters then starting with an e30 is doing it wrong anyway, an e36 compact handles similar but with more grip, better brakes and cheaper easier engine swaps.

Forget sticking a 731 head onto an eta bottom end, its quick and easy and gives some nice torque but your only looking at 180hp as the 731 head just cant feed an 84mm bore without a lot of work. Its like taking a 318is motor out to stick a 320 motor in, waste of time.

Getting the b20 block bored to 84mm is a good plan as you get a nice fresh block, however do get your machine shop to check the block very carefully for thickness before you do, the b20 block will go to 84mm fine but will be thinner than a b25 block which can safely go to 86/87mm.
From my research and asking about i have come across a few b20 blocks that had broken through on one bore or bores cracked later on.
I think it was ~4.5mm minimum thickness needed after boring.

Both pistons when fitted with 130mm rods and an 84mm stroke 2.8 crank will end up 0.5mm lower than standard so a 0.5mm skim will be needed from the block face to get back to standard.
(i.e. 2.5 = 75mm crank and 135mm rods, normal piston = 75/2+135 = 172.5mm
2.8 = 84mm crank and 130mm rods, same pistons = 84/2+130 = 172mm or 0.5mm less. )

The shortening of the skirt on a high comp piston for a single vanos crank is like this:
Note how the skirt ends around 5mm below the pin boss cut out.



If your taking the head off and refreshing the head, do get a performance cut done on the valve seats, it works out at about £15 a seat and really helps, any modern performance cut will prove better than the 1980s standard cuts.

I got quotes for everything needed to do a good job of a 2.8 build for alex a while back and via zone ecp discount and cotswold bmw the parts came to ~£600 without shells or rings. (that included machining work from my local place, multi-angle seats and a hone and skim).

Remap wise i would advise that you ask the chip tuners on the zone, one of them will have a map that will be perfectly fine for what your building as you are not going too far away from a run of the mill stock 2.8 build. Costs will be £50-100 rather than the costs of a custom live map session.

Expect around 185-205hp depending on exact spec.

[Gunni]

E36s don´t have more grip then E30´s. The reason is that E30´s make for better drag cars then E36´s even with stock rear ends. E30´s have been in the 8s with stock rear ends.

It´s all about the tires.

[HairyScreech]

Indeed the tyres are the most significant factor, however I personally believe the potential for mechanical grip is higher on the e36 compact than the e30 due to the wheels that can be fitted to a stock body, the 9" extra length in the wheel base, the 4" less total length and 2" extra width and the reduction in overhangs, this is without considering the increase in stiffness of the chassis from the e30 to e36.

e30s may make better drag cars but that is a different kind of grip, what works for a pure drag car that can run 8sec passes can't work for circuit or track day/road work.

However that is an aside to this thread, perhaps it deserves a thread in its own, the discussion could be quite interesting (and heated knowing the way any thread about the e30s technical inferiority goes).

[Kieran_n22]

Put the B28 in as it is. More low end, more high end, better fuel economy

that was my plan but with the costs of a new head + the other stuff to fit it is gonna be crazy!
Does anybody know what head the early engines have on the 2.5?
hmm so now I have to think whether I want to bore my 2.0 as it's out of the car and accessible or wait until I take the 2.5 out.
I'm gonna have to get my head around all these mm sizes to get skimmed and stuff so I know exactly what to do.
What shall I do now then? Rip open the B20 for the conrods and B28 for the crank?