E30 engine options

[Iain]

Stroked original M20 (2.5L SOHC 12valve "boat anchor") or E36 M50 (2.5L single VANOS DOHC 24valve).

Before anyone says it: no turbo, no M30, no S50. Worked M20 or mild M50 only.

Rebuilding the M20 would involve stroking and boring its capacity out to 2.8-litres by using a 2.7-litre 325e/525e crankshaft, increasing the compression ratio to 10.5:1 by using new pistons, freshening the whole bottom end (rings, bearings), lumpier camshaft for extra grunt, piggyback ECU to manage newfound performance parameters, new valvetrain and port/polish of head as well. This would give the aforementioned 200-ish kilowatts. I could buy a “spare” M20B25 and sling it in my car, while stripping my current motor and building up that over time. It would minimise “down time” for the car being off the road, too.

M20 stroker rebuild needs around $10,000 (max) and will give over 200kW, will will knock my fuel consumption down and need more regular maintenance. I would need someone to do custom tuning on the motor to set-up the ECU. A benefit is that I could buy another stock M20B25 cheap, put that in my car and build my current motor on a bench over time, then simply swap the motors around when the new motor is complete.

The M50 needs plenty of work to allow it to fit in the engine bay. All the ancillaries need to be moved or customised, from brake booster, to engine mounts, gearbox mounts, pipework, etc etc. Ideally, while the motor is out of the car, I would fit a chip and lumpier camshafts, possibly ones from a US-spec 3L M3, though this would increase the cost of the transplant considerably.

M50 swap needs around $5000 and will give ~140kW, better fuel consumption, smoother motor, more potential for liberating power. It is, however, much more expensive to modify and even as a stock motor, is more expensive to maintain. However, I would not need custom tuning as I would with the M20 as it is simply plug-and-play.

Basic parts lists
M20:
- Eta 2.7-litre crankshaft
- 10.5:1 c/r pistons
- fresh bottom end (rings, bearings)
- port/polish of head
- new valvetrain/rocker gear
- Schrick 288deg or 272deg camshaft
- Ford XR 19lb injectors
- M30 air-flow meter
- all new gaskets
- piggyback engine management system
- new upgraded clutch

M50:
- Japanese import, low km engine (E36 325i/E34 525i)
- E21 323i brake booster
- E28 535i engine mounts
- new clutch
- new tailshaft flex disc
- custom headers
- wiring adapter
- E36 325i engine arms
- Injector cleaner
- E36 325i intake support
- custom air intake piping/AFM mount
- custom gearbox crossmember
- custom shifter linkage

[MrBlonde]

Is that a question?

[seetwo]

Judging by what's proposed, I'm all for the M20... a worked E30M20 will give you a far better result than a close to standard E30M50 will.

Fuel consumption really shouldn't be on your mind if you're working a motor up in my opinion.

As for the M50 being a smoother motor, I think you'll find that a freshly rebuilt M20 isn't any less smooth...

I think the M50 conversion is a little overrated, though I'd like to hear some arguement from those who've performed it... might change my mind...

[spankerdan]

in time i will be doing an engine swap and the same options you've outlined above is the same i was thinking about... but not as much work to the m20.

the difference between our motors is i have an m20b20 so id try and find a better condition m20b25 and put that in instead with minor work... i think this option would b alot cheaper than the m50 but being an older engine it may need some extra repair work.

im still up in the air about what to do

[Aaron318iS]

Total E30 n00b here so I don't know the ins and outs of what you're doing exactly but if you're considering swapping in an M50 2.5, any reason why you couldn't go for an M52 2.8? Then you'd have a newer engine with more potential as you put it.. with same capacity as a stroked M20?

[CafeRacer]

ive had the same thoughts, im all for the M20 build up. More power, looks more original, less time and at the end you have a 100% fresh engine rather than an apparent low kms that you really arent sure what condition its in.

[spankerdan]

Originally Posted by Aaron318iS

Total E30 n00b here so I don't know the ins and outs of what you're doing exactly but if you're considering swapping in an M50 2.5, any reason why you couldn't go for an M52 2.8? Then you'd have a newer engine with more potential as you put it.. with same capacity as a stroked M20?

aaron i think it is because the m52 is much harder to find than the m50... if i could infd an m52 id go for that..

its like the s50/s52 conversion... you see alot more s50 e30's... this may also have something to do with the more sophisticated electronics of the s52 (correct me if im wrong)

[1q2w3e4r]

Originally Posted by spankerdan

aaron i think it is because the m52 is much harder to find than the m50... if i could infd an m52 id go for that..

its like the s50/s52 conversion... you see alot more s50 e30's... this may also have something to do with the more sophisticated electronics of the s52 (correct me if im wrong)

Who's done S52 conversions in Australia?

[babbo]

Why play with old technology when you can play with new?
M50 it up!

Ben, the conversion for an S50B32 isn't that hard if you've got the right bits.

[SIR325]

just out of curioisty for the M20 option, would you be doing all the work yourself or basically hand over the cash and let somebody else do the work, and i know its like asking "how long is a peice of string" but how long would the car be off the road with the M20 option, and is the 200kw'ish estimated or a proven power figure, if so does anyone need there lwans mowed/pools cleaned?

[1q2w3e4r]

Originally Posted by babbo

Why play with old technology when you can play with new?
M50 it up!

Ben, the conversion for an S50B32 isn't that hard if you've got the right bits.

I know mate. But the S52 is the US of A boat anchor. Can't fathom why someone would even bother pissing on it when you could use the S50B32 as you said or B30

[Iain]

Thanks for all the replies, guys.

I want my car to be balanced. I don't want 400hp 'cause its too much, I want good handling, not outright G-forces. Basically, I'm building it like a tarmac rally car, or Japanese "Touge" mountain racing machine

With this in mind, I'm thinking more and more of the M20, and a big factor in this decision I've explained below (down/off-road time)

Originally Posted by SIR325

just out of curioisty for the M20 option, would you be doing all the work yourself or basically hand over the cash and let somebody else do the work, and i know its like asking "how long is a peice of string" but how long would the car be off the road with the M20 option, and is the 200kw'ish estimated or a proven power figure?

Ok dude, the plan is to buy a cheap M20B25, swap it into my car for daily driving duties, pull my current engine out and strip the sucker down nekkid. Then, I'd order the parts through my mechanic (who has a 2.8 325iS among a host of other cars) over time, but I'd be doing much of the assembly myself at home, again over a few months. I'm thinking a 288deg cam is overkill, so (thinking out loud here) I'd probably go a 272deg jigger to keep low/mid-range response.

I would then take the car to him to get him to fit the EMS and tune it all. I'd gradually build it up, step by step, piece by piece, all the while keeping the E30 on the road, eventually dropping it back in over a weekend (with fresh clutch, etc).

Well, that's the PLAN anyways...

[NTR325]

'Iain' - definately like the plan. Good luck with it all

[1q2w3e4r]

Originally Posted by Iain

Thanks for all the replies, guys.

I want my car to be balanced. I don't want 400hp 'cause its too much, I want good handling, not outright G-forces. Basically, I'm building it like a tarmac rally car, or Japanese "Touge" mountain racing machine

With this in mind, I'm thinking more and more of the M20, and a big factor in this decision I've explained below (down/off-road time)


Ok dude, the plan is to buy a cheap M20B25, swap it into my car for daily driving duties, pull my current engine out and strip the sucker down nekkid. Then, I'd order the parts through my mechanic (who has a 2.8 325iS among a host of other cars) over time, but I'd be doing much of the assembly myself at home, again over a few months. I'm thinking a 288deg cam is overkill, so (thinking out loud here) I'd probably go a 272deg jigger to keep low/mid-range response.

I would then take the car to him to get him to fit the EMS and tune it all. I'd gradually build it up, step by step, piece by piece, all the while keeping the E30 on the road, eventually dropping it back in over a weekend (with fresh clutch, etc).

Well, that's the PLAN anyways...

Sounds good.

But. Isn't your car already a 325? Hence has a M20B25 in it. So why bother buying an old motor and swapping out your current one to rebuilt the same engine. And then swap it back in.

It'd be a lot less hassle to buy an engine, tear it down and have it rebuilt and then when it's finished just rip your old one out.

Why pull out and swap the same engines? Just buy one have the mechanic built it to your specs and drive around as your car is till it's all done.

[europhile]

Originally Posted by 1q2w3e4r

Sounds good.

But. Isn't your car already a 325? Hence has a M20B25 in it. So why bother buying an old motor and swapping out your current one to rebuilt the same engine. And then swap it back in.

It'd be a lot less hassle to buy an engine, tear it down and have it rebuilt and then when it's finished just rip your old one out.

Why pull out and swap the same engines? Just buy one have the mechanic built it to your specs and drive around as your car is till it's all done.

I agree, just buy an engine and build it, then drop the new motor in.

In favour of the M20 is weight, and more importantly, weight distribution. You mentioned that you were seeking balance and good handling from your car; the M20 is considerably lighter than the M50 (117kg vs. 194-198kg) which would produce less understeer, and being SOHC it has a lower CoG which would improve the balance, and overall handling of the car.