BMW 635 CSi M30 engine questions

BMW 635 CSi M30 engine questions

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Ian_UK1

Original Poster:

1,495 posts

157 months

Wednesday 6th November 2013
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Hi everyone - my first post in the Engines and Drivetrain forum after a long time lurking!

I recently bought a 1985 BMW 635 CSi as something of a project. I was lucky to find a car free of the usual rust, rust and more rust, but at 28 years old and 114,000 miles it's certainly 'tired' - mostly around the suspension, steering and electrical departments.

Once I've got the rest of the car in shape, the intention is to rebuild the engine (and also to include some improvements/updates during the build). Hence the post here.

I've a few questions I'm hoping those more knowledgeable than me might be able to answer:

1) Is there anyone left in the UK who's really knowledgeable where these engines are concerned? A good engine builder would seem to be the right place to start.

2) Does anyone have experience of modifying the M30 cylinder head? Head work (I'm assuming around the valve seats/throats not cosmetic port-polishing) seems to be key to getting good results from this engine.

3) It would appear to be possible to obtain a smooth, torquey, driveable 260BHP or thereabouts from the 3.4 engine. Alpina-modified engines were producing this kind of power back in the day. Putting together all the info I can find, the Alpina modifications included a flowed head, bigger inlet valves, different cam (no idea of the spec) different pistons and appropriate mapping changes. 75BHP/litre doesn't seem a bad result from a relatively low-revving 12-valver. Is this the sort of output I should realistically be aiming for?

4) Would anyone know where the limits of the old Motronic engine control systems lie (in terms of ability to measure airflow and the injectors ability to supply fuel)? There must be a practical limit where the system approaches 100% injector duty cycle. Would this happen before our theoretical 260BHP is reached, or would the system theoretically cope with that kind of output? I'd also be interested to know how difficult it would be to change the fuel and ignition maps as required.

Thanks in advance and looking forward to any guidance you might be able to offer.


rossb

581 posts

184 months

Thursday 7th November 2013
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Mark Mclennan used to do stuff for me on old BMW's in Dorking surrey - not sure he has a web site but 01306 713232 was the number i found after a google - he used to race a 6 series amongst loads of other bmw racecars - and read on the web he does stuff for 4star classics who sell quite a few 6 series

Ant Woodjets who ran A Tech - not sure he is still in business was a wizard on trick modified six pots that found there way into E30's which included the m30 - this was his number - 07787 114963 - was based in kent

he worked with a mate of mine on developing a supercharged e30 with a 2.7 m20 with an eaton m90 blower off a db7 that i had years ago - drank a lot of beer in my garage trying to get that thing to run! i think i used m30 bosch injectors in my engine and that had a reasonably high demands on fueling - but someone like mark or ant would be able to advise - here's an old vid of the car which i sold for a 1/5th of build cost years ago - it was the car that cured me of doing something "different" ever again -

http://www.youtube.com/watch?v=BSYN1saHslk

what i remember about the m20's and M30's was that bottom end's were strong - standard flywheels were heavy - Schrick were the go to cam manufacturer - i used megasquirt for sparks and fuel - only kept the motronic to run the dash - we just cleaned the head up to due to the blower and did not bother with big valves etc - remember Ant getting 250 bhp out of a naturally aspirated stroked 2.8 M20 so i doubt 260 out of a 3.5 m30 is a big ask. loads of people used to just drop lightly breathed on M30's into e30's for lightly stressed q car with ample capability to steer off the throttle.

Good luck!

Pumaracing

2,089 posts

170 months

Friday 8th November 2013
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Ian_UK1 said:
75BHP/litre doesn't seem a bad result from a relatively low-revving 12-valver. Is this the sort of output I should realistically be aiming for?
Regardless of the capacity of an engine it's the head flow that limits power and bhp/litre isn't really a measure you should be going by. The M30 has nice big valves (46mm in the B4 and 47mm in the B5) but it also has a lot of capacity for them to feed so it isn't over-valved by any means.

The inlet ports are slightly unusual with the oval manifold ends merging into the round throat. They're also quite short and not very downdraft so the key areas are getting the radius of the shortside bend and the valve seat and throat geometry correct. The chamber is fine and not flow restrictive being basically a hemi with a couple of areas filled in to generate squish bands. In porting terms it's not that dissimilar to a Ford Pinto in a lot of respects. There are goods gains to be had over stock but it won't flow to the same efficiency as more downdraft ports like a Ford CVH or most 4v heads.

If you can bear to plough through the following thread I give some porting guidelines for general application.

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

As to your power potential it depends what you do on induction system and cam choice. With a well ported 47mm valve head, retaining a plenum manifold, good exhaust and a fairly rorty but still driveable road/mild rally cam you should be looking at about 250 bhp. If you went to ITBs and fully mapped fuel and ignition to get the optimum induction system and a bit more cam you could certainly be hitting 280 bhp but at fearsome cost.

If you're expecting 260 bhp from simple mods it's a tad optimistic.

Kokkolanpoika

161 posts

114 months

Friday 8th November 2013
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250-260hp is quite hard to achieve if use STD 3.5i heads say 1989year.. (not sure if older heads are same) We have build couple of those engine in Finland, both give approx 236-240hp and 310-326Nm.. The short side radius is tight like pumaracing say.. first engine use Alpina camshaft, and 2nd one use schrick camshaft, slightly more degrees than alpina cam.. drivebility is good, but idle quality is slightly rought for schrick cam..
Inlet side: there is not mutch material to remove, better to fill floor to make good port.. If remember correct,ported head will flow ~+300hp

In the same money you will buy e34 M5 engine(S38B35)Like my friend did(after trying to tune his M30),and i made swap his E30.. But M30 will give mutch mutch more low down torque..

Ian_UK1

Original Poster:

1,495 posts

157 months

Tuesday 12th November 2013
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Thanks for the responses so far - I really appreciate the knowledge each of you is prepared to share.

The engine in my car is one of the 10:1 compression lumps with the 46mm inlet valve, not the later 9:1 versions with the 47mm inlet valve. It would seem to make sense to put the bigger valves in the existing head whilst retaining the higher compression ratio. In theory this should increase the engine's output across the rpm band. Looks like a Schrick cam (280 degrees ish?) is the best currently available bump-stick and would add a little more across most of the rpm band too.

As the bottom-end will need a refresh, the pistons can be replaced if more clearance is required for the larger valves/different cam. Hopefully some can be found that will still give a 10:1 or higher compression ratio? Balancing the crank/rods/pistons/flywheel would seem sensible too.

The one item I'm having absolutely no joy with is an exhaust manifold for this car. The standard manifold is truly horrible as it has to squeeze past the large steering box that's primarily designed to be on the other side of the engine bay (and is right in the path of the exhaust in a RHD car). I can't see it not strangling the engine to death. The problem is that extractor manifolds - all designed for LHD - won't fit (again due to the steering box location). I'm guessing that the more we increase the ability of the engine to flow air, the more of a restriction the exhaust manifold will become. Anyone have any ideas where I might get a custom manifold made?

That just leaves the induction system and fuelling. To keep costs sane, I don't want to replace the manifold/plenum or old Motronic wholesale for now. I would consider replacement of an individual element if it's strangling things to the point where the other mods won't work though. As the factory ignition mapping will unlikely be even close to optimal for the new engine spec, I'll be looking for a way to remap appropriately. I'm guessing the Alpina map would be a reasonable starting point as the motor's spec will be similar. Does anyone know if that map is 'in the wild' anywhere? Maybe Wayne Schofield (Chip Wizards) might be a good place to start?

Question for Pumaracing. I know from reading many posts you've made on here that you're very knowledgeable where cylinder head mods are concerned, but do you actually undertake head modifications yourself? (Apologies in advance if it's a stupid question, but I know nothing about you or what you do). The thing I want to avoid is making the mistake of sending the head to a 'port-polisher' (and ending up with a very shiny, but all-show/no-go result). If this is something you don't do, is there anyone you can recommend who will apply the principles you explain so well and re-work the car's head to good effect for me?

Thanks in advance once again.



Edited by Ian_UK1 on Tuesday 12th November 18:41

PeterBurgess

775 posts

109 months

Wednesday 13th November 2013
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Hi Ian

Check with the cam supplier to ensure the profile will not upset the fuelling too much. Most efi likes more airflow up to say 25% before upsetting fuelling whereas pulses from radically different cams can upset the fuelling apple cart.
If you need to work hand in hand with someone to do the head, we have a lot of experience with the 4 cyl version of your head going back to around 2000 when we worked on Historic Touring Car BMWs for a couple of Race firms, we coined the word obround to describe the transition from the oval port to the round valve throat of the BMW inlet ports! The Schrick cams and valves we worked with were very effective.
We do all our head work in house and have our own rolling road if you fancy doing before and afters for realistic feedback for your tuning journey.

Peter

Pumaracing

2,089 posts

170 months

Thursday 14th November 2013
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Although my website is not currently online (long story) everything has been archived by the Wayback Machine so you can follow the links off the index page to my company history and also I suggest the tuning and technical articles will answer many of your questions about power potential and other things such as exhaust design.

https://web.archive.org/web/20120115101521/http://...

I'm currently setting up a new workshop having moved from London to north east Scotland but when, or even if, I'll be taking on anything other than for my own cars and friends is less certain. Best to ask nearer the time if you decide to go ahead.

The Bosch Motronic injection system on your car, or at least its air flow meter, really doesn't like long duration cams which is why I said that more cam than fast road would go better with ITBs and fully mappable systems.

However it should be able to cope with reasonable airflow and power increases but you need to find someone familiar with setting it up before planning any mods. Wayne would be a good starting point.

I'd be surprised if your exhaust manifold is as restrictive as you think but photos and dimensions would help.

DVandrews

1,162 posts

246 months

Thursday 14th November 2013
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Before you do any work on the head, examine the top surface of the head under the cam bearing towers, they are prone to cracking along the length of that area which breaches the coolant jacket in the head. Look very carefully.. They can be repaired but not all will succeed.

Dave

Pumaracing

2,089 posts

170 months

Saturday 16th November 2013
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I should just add one thing. Whatever you decide to do I would suggest it makes sense to just bin the stock ecu and go fully mappable, even if you keep the standard plenum to save the cost of ITBs. You don't need a fancy mappable system. Just a very basic one that maps off a throttle position sensor and then you can ditch the flappy valve air flow meter which limits your choice of cam, have any ignition advance curve you need and get the fueling properly set up instead of having to try and tweak and butcher a Motronic system that was never designed to be altered.

You'll get much better low rpm tractability like this and easier adjustment for future mods and possibly not even cost much more overall because mapping will be easier and quicker and the labour cost of doing that is a big part of the overall package these days.

PeterBurgess

775 posts

109 months

Saturday 16th November 2013
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Funnily enough Dave that is exactly what Carl said from Norris Motorsport (neighbouring unit to us), I asked what he thought of the OE system and he reckoned junk it and fit Omex, as cheaper and better in the long run.

Peter

stevieturbo

15,244 posts

210 months

Saturday 16th November 2013
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PeterBurgess said:
Funnily enough Dave that is exactly what Carl said from Norris Motorsport (neighbouring unit to us), I asked what he thought of the OE system and he reckoned junk it and fit Omex, as cheaper and better in the long run.

Peter
And then turbocharge it lol

ash635

33 posts

164 months

Sunday 17th November 2013
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I suggest you look on Bigcoupe.com, they are a dedicated 6 series website with lots of useful information.

Regards
Ash

Ian_UK1

Original Poster:

1,495 posts

157 months

Monday 18th November 2013
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Once again, thanks for all the responses so far - some really useful info.

I'm sure the advice to swap-out the old Bosch Motronic with the flap/gate style AFM is sound. I've encountered issues with this type of AFM donkeys years ago. On what make/model of car, I don't remember, but I do remember the 'reverse-airflow' at low RPM (caused by a lot of overlap) creating all sorts of unwanted oscillations in the AFM flap and the fuelling going to hell. I vaguely recall later flap-type AFMs having an additional element to the flap (and an additional, closed-off air channel at 90 degrees to the normal intake flow) that was supposed to smooth these issues out to some degree. I've no idea if it was effective. So, an interesting dilemma - go more radical on the cam and replace the engine management or use a relatively tame cam and keep the Motronic for originality.

To PeterBurgess - thanks for the info about the work you've done on the M10 heads. Very interesting. I'm assuming, if this work translates directly to the M30, that the M30 head is essentially 1.5 M10 heads end to end? Will come back to you next year at engine rebuild time.

To StevieTurbo - nice idea, and I believe the M30 responded very well to turbocharging back in the day. The main problem seems to be RHD - there's that stonking great steering box in the way of where the turbo would go.

To Dave Andrews - thanks for the info about potential cracks in the head/coolant jacket - I'll check that area carefully as the engine's stripped down next year.

To PumaRacing - I'll try to find some pics of the horror that pretends to be an exhaust manifold on the RHD version of this engine. It's affectionately known as the 'Dingolfing Engine Strangler' in the E24 community! smile

To Ash635 - thanks for the heads-up. I do already lurk around the Bigcoupe site, but find it better for DIY tips than full-on practical help about major projects like engine development. Masses of back-catalogue to search through yet though, so I might still find more relevant stuff.

Ian






PeterBurgess

775 posts

109 months

Monday 18th November 2013
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That is a busy reply Ian smile

If you would like to bring your head up you can put it side by side with the 4 cyl variant and compare/discuss/contrast (sounds like a history exam!)over a cup of tea/coffee or noodles if still winter.

Peter

Output Flange

16,409 posts

174 months

Friday 6th December 2013
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Did anything happen with this? I've got a 535i that I'm looking into similar options for - going to ITBs is a no-no as this is a race car and the regs don't allow it, but I'd like to get a bit more oomph, and head work/cam seems the best starting point.

e21jason

713 posts

182 months

Monday 23rd December 2013
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Quite a few people still work on these engines, there is no real magic just good old engineering.

You want the later motronic of an e34 as it is more tuneable and with a millar war chip can be converted to stand alone.

Fritz bits do a six branch manifold

Place like VAC/Korman/topend/Ireland engineering in the states do trick bits like billet cam followers etc.

I have a spare alpina head and compared to a stock head the porting is not hard to replicate

Very easy to adapt m5 throttle bodies you used to be able to buy the adaptors on ebay.de for 100 euro.


M5Player

97 posts

180 months

Wednesday 25th December 2013
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260bhp should be fairly easy to achieve. I run a three litre M30 and it has road manners with an output circa 275bhp on triple 45's. I had mine built by Lester Owen.
Further to comments above I actually ended up chucking the fritz manifold due it's poor performance and had a proper equal length one made.

Ian_UK1

Original Poster:

1,495 posts

157 months

Sunday 9th March 2014
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M5Player said:
260bhp should be fairly easy to achieve. I run a three litre M30 and it has road manners with an output circa 275bhp on triple 45's. I had mine built by Lester Owen.
Further to comments above I actually ended up chucking the fritz manifold due it's poor performance and had a proper equal length one made.
Where did you have the manifold made? I've tried a couple of exhaust manufacturers locally, but nobody seems remotely willing to assist. Ditching the dire, factory exhaust manifold would be quite high on my list of priorities!


stevieturbo

15,244 posts

210 months

Sunday 9th March 2014
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Ian_UK1 said:
Where did you have the manifold made? I've tried a couple of exhaust manufacturers locally, but nobody seems remotely willing to assist. Ditching the dire, factory exhaust manifold would be quite high on my list of priorities!
Lance at OJZ Engineering will make you whatever you want, and do a bloody superb job of it.

Ian_UK1

Original Poster:

1,495 posts

157 months

Sunday 9th March 2014
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I'll be contacting him tomorrow - many thanks for the recommendation