To M52 or not to M52?

[andrew_baran]

I've been offered an M52B28 with gearbox, ancillaries, ECU, EWS, etc for a very good price. But i'm torn. I don't know whether to take the offer up and go for it, or to enjoy the M20B25 in its intended origin.

Pros for the M52/Cons for the M20:
- More power and torque
- Noticeable as an engine swap when the hood is opened!
- Better exhaust note from the M52
- Fuel efficiency increase (lol)

Cons for M52/Pros for the M20:
- Price of parts inevitably missing from conversion
- M52 not being an original E30 engine.
- Possibility of getting a duff block after reading Magpie's build!
- Insurance increase

I only changed my high comp M20B25 in a few months ago from an M20B20, so it kind of feels a shame to change so soon. But on the flip side... M52 power....

[Speedtouch]

I would personally stick with the venerable iron block M20B25 anchor, particularly if it's a high compression one, for the sake of reliability.

You hear so many horror stories about these later alloy block BMW engines.

[Rich320I]

I would personally stick with the venerable iron block M20B25 anchor, particularly if it's a high compression one, for the sake of reliability.

You hear so many horror stories about these later alloy block BMW engines.

+1

a decent solid high comp m20 is not a bad power plant

[Motorhole]

I'd say go with the M52 but don't underestimate the cost of a proper conversion.

I disagree on sound being a pro for the M52 though! I reckon the M20 offers the better soundtrack.

[polsta]

If its a nice example car, keep the m20, too many engine seals these days , spend the money getting it bang on, refurb the head etc or a full rebuild and getting it running like new

[andrew_baran]

Re. the noise - this video is my old E36 328 with an aftermarket exhaust on it - I miss this soundtrack so much...

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[Blitz]

That does not sound nice.

[penton08]

M20 wins for sound IMO, m52 wins for everything else.

[hillbilly30]

I think the m52 sounds totally different in the e30, the exhaust makes it sound more retro! I would say the m20 is fast "enough" and as long as that is enough all good but the m52 even in the e36 is so much stronger through the revs, I imagine in the e30 it feels very quick, I know an s50 in an e30 feels nutty compared to an e36 m3
But, I've never had a problem with an m20 or an m52 so reliability is prob more luck!

[B7]

Surely it depends on what exhaust you have??

Back to the argument. I'm an M20 man. I think the 52 looks wrong in the bay and a good 2.7 / 2.8 build keeps the bay looking ight and gives good torque and power.

There. I said it.

Why not source an m20 at a reasonable price and build a 2.7 / 2.8. Keep your car on the road and when the new ones built, just a straight swap over. If you don't like it, it doesn't work out or want to return to original, you still have all the old engine and ecu to get the car back to normal.

[penton08]

The exhaust does make the sound different but a m20 always sounds like an m20 if you know what I mean. I'm in the other camp with regards to looks, I think the m52 looks better in the bay and a s50 looks so "right" in a e30 engine bay

[AndyZippy]

Re. the noise - this video is my old E36 328 with an aftermarket exhaust on it - I miss this soundtrack so much...

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Sounds filthy - i love it!

[jmc330i]

I'm in the other camp with regards to looks, I think the m52 looks better in the bay and a s50 looks so "right" in a e30 engine bay

S50 looks perfect in the E30 engine bay, M20 comes second, M52 third - the M20 definitely has the best exhaust note by far.
Although, the induction noise of an S50 under load on WOT with an open air filter is very addictive (and a close second to the M20 exhaust note), especially when the Vanos kicks in


Personally I'd be sticking with the M20 (having done 24v swaps), there are a lot of conversions out there, it would be good to do something different and keep a 12v lump!

[hillbilly30]

If I'm totally honest if my "is" had been a 2.5m20 it would still be in there now, it was only as the leap from m42 was so great it was worth doing, need to change my vote I think! I jumped to the defence of the 52 too quickly

[andrew_baran]

Thanks for the replies - a very even result! I think for the sake of getting a manifold and exhaust adapted; the associated costs i.e. clio servo, service parts etc. i'll just stick to my M20 and get it running tip-top!

I've booked the car in on Saturday to get the centre silencer removed though - see if I can unleash some of this M20 noise you are all so adamant beats that M52!!

[Quaser]

If the car was an original 325i, id say stick with it.

As its not the original engine anyway, then the m52 looks nice in the engine bay. Did you get some parts off my red touring? I think you heard the sound track of my m52 cab didn't you?

If your gonna stick with the m20, you could spend the money sticking a turbo on it!

[suchy]

I like the M20 myself and would rather pour the money a proper conversion will cost into the M20 on a rebuild and further 'enhancing' work. I'm also a bit of a bender for matching numbers and all that gay stuff. Seeing as you've already had a swap, this point is moot!

I think an M52 done properly with the right bits (intake, flywheel, cams, manifold, exhaust, etc.) is quite a weapon, but all adds to the cost. If it was a choice between a bog standard swap then I'd keep the M20. HKF used to have an M52 with the intake and a chip and it was pretty quick!

Isn't the M52 a bit peaky though and lacks that low-down grunt of the M20 (torque FTW)??

If I was planning an engine swap, I would go M30 as it's more of a 'period' mod

[andrew_baran]

Quasar - yes that was me. I did see and hear your M52 cabby, it was very, very nice!

The M20 turbo conversion would be great, but I've got a high comp M20, which would mean i'd be better off swapping it out all over again before turbocharging it. M50 non-vanos Turbo? Hmmm....

An M52 conversion wouldn't be worth it without the M50 manifold, chip and M20 flywheel - "whilst you're there" and all that...

[Demlotcrew]

That does not sound nice.

I thought it sounds okay

[Quaser]

you can get decompression plates / thicker headgaskets etc to lower compression

Anyway, im looking to get a touring to turbo

[daimlerman]

I have a 2.7 engined cabbie and an M50'd touring.....

The touring ran 13k miles last year,the cabbie about 2k...

I have made an effort to use the cabbie more this year,but the touring is just so practical as a 'boat tender',hauling timber and tools at speed without protest.

While I can see the 'looks stock' points regarding a stroked M20,the cost of building these engines needs to be carefully researched.My 2.7 cost upwards of £1500 to build some years ago,and those zoner's who have built 2.8's are admitting to £2k+ build costs.

So from both a money and performance POV,an M52 does look to be value for money.
However,I would be tempted to base the bottom end on a cast iron M50 block!

[Andyboy]

Surely it depends on what exhaust you have??

Back to the argument. I'm an M20 man. I think the 52 looks wrong in the bay and a good 2.7 / 2.8 build keeps the bay looking ight and gives good torque and power.

There. I said it.

Why not source an m20 at a reasonable price and build a 2.7 / 2.8. Keep your car on the road and when the new ones built, just a straight swap over. If you don't like it, it doesn't work out or want to return to original, you still have all the old engine and ecu to get the car back to normal.

Me too. A well built 2.8 M20 looks stock, sounds nice and goes well enough.

[Andyboy]

My 2.7 cost upwards of £1500 to build some years ago,and those zoner's who have built 2.8's are admitting to £2k+ build costs.

Gold plated piston rings?

An M20 325i engine is £250. A 2.8 short engine for the crank is £50-100. Six 320i rods £50. Gaskets, oil seals and rod bolts are £175 ish. Machining £150 to deck the block and head, head pressure test and chemically clean everything. £100 for rings. That's £825, plus the cost of a nice cam. Realistically, it's around a grand with a standard cam.

[randomspeedfreak]

4 valves per cylinder > 2 valves per cylinder

[daimlerman]

My 2.7 cost upwards of £1500 to build some years ago,and those zoner's who have built 2.8's are admitting to £2k+ build costs.

Gold plated piston rings?

An M20 325i engine is £250. A 2.8 short engine for the crank is £50-100. Six 320i rods £50. Gaskets, oil seals and rod bolts are £175 ish. Machining £150 to deck the block and head, head pressure test and chemically clean everything. £100 for rings. That's £825, plus the cost of a nice cam. Realistically, it's around a grand with a standard cam.

You forget that you need a gadget machining to suit the crank/block front oil seal.
You also disregard any need to check/re-grind the secondhand crank that you have bought....
Then there's the new head bolts,flywheel bolts....it all adds up!

[Andyboy]

You forget that you need a gadget machining to suit the crank/block front oil seal.

£30.


You also disregard any need to check/re-grind the secondhand crank that you have bought.

Use a micrometer! All the M52 cranks I've had have been perfect.

Then there's the new head bolts,flywheel bolts....it all adds up!

Head bolts £16. Flywheel bolts around £3.50 each iirc.

[daimlerman]

You forget that you need a gadget machining to suit the crank/block front oil seal.

£30.


You also disregard any need to check/re-grind the secondhand crank that you have bought.

Use a micrometer! All the M52 cranks I've had have been perfect.

Then there's the new head bolts,flywheel bolts....it all adds up!

Head bolts £16. Flywheel bolts around £3.50 each iirc.

You assume that your s/h 885 head is fully servicable with 'just' a chemical clean and a skim?

Bet you need at least 6 exhaust valves at £12 each,12 new rockers at,what?,£14 each,new valve guides at £10 each.....
Perhaps a few valve springs?

All adds up,that is,if you want a 'proper' engine that will run for a few years.

[Andyboy]

You assume that your s/h 885 head is fully servicable with 'just' a chemical clean and a skim?

Should be.

Bet you need at least 6 exhaust valves at £12 each,12 new rockers at,what?,£14 each,new valve guides at £10 each.....
Perhaps a few valve springs?

Nope. Buy a clean head and the guides will be okay and the valves will lap in nicely.

All adds up,that is,if you want a 'proper' engine that will run for a few years.

Spending money is easy. Reusing serviceable components is also easy!

[daimlerman]

On the other hand,Andy,remember that M50 you helped me drag out of the Calypso E34?

Fitted a s/h cluster to the touring that showed 123k,same cluster now shows a whisker over 170k,all the engine has had is oil/filter as requested by the SI,a radiator to replace the ex E34 item,and a new battery.

M50/52 all the way!

[maggspower]

The real stingers are the rod bolts, they are single use. Do you reuse those

They are £65 now, and BMW only.

[breakermart]

im saying m52 probably because im currently doing it to my e30. iv not had the pleasure of seeing one on the road nor have a go in one, so very much curious as to how the e30 feels with such a lump fitted! ..... oh yeah, wouldn't that go down as a con against the m52, the front end will be nose heavy and not so perfectly balanced out like the e30 was originaly?!?! oh well this is my botherd face lol

[Quaser]

I think the m52 is lighter

[hillbilly30]

im saying m52 probably because im currently doing it to my e30. iv not had the pleasure of seeing one on the road nor have a go in one, so very much curious as to how the e30 feels with such a lump fitted! ..... oh yeah, wouldn't that go down as a con against the m52, the front end will be nose heavy and not so perfectly balanced out like the e30 was originaly?!?! oh well this is my botherd face lol

FYI the m52 feels like a lottery win! Or like coming home from work to find your mrs's t1ts are twice the size they were! It does make the day your first child was born seem a little insignificant though