BMW 635 CSi M30 engine questions
Discussion
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.
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.
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.
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
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!
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
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!
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
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!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.
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff