E46 330Cd (M57N) Single (Solid) Mass Flywheel (SMF) - Review and Daily Drive Feedback

I have spent countless hours looking for someone who has installed a solid flywheel to a road going M57N engine however I could not find 1 post with someone who uses a solid flywheel on a daily basis.



So I bit the bullet, did some research and ordered a solid flywheel, uprated pressure plate and 800nm clutch. I have listed the history as to how I ended up needing a solid flywheel, so if you are heading down my route you will know where to stop and what sort of choices lie ahead.



When I purchased the car I installed a new dual mass flywheel,pressure plate and clutch (stock power so 204hp).



I then got the car remapped to a decent 250 bhp which was the limit of the new dual mass (when mapped first the DMF would vibrate on full throttle so the torque was reduced slightly to illuminate this). With this map I could use any gear at any rev, get no clutch slip and no flywheel vibration. This was at 110,000 miles. Stick with a DMF at this power as there is 0 benefit going to a Single Mass Flywheel(SMF).



At about 125,000 miles I went for a c. 280-290bhp map which consisted of a considerable increase in torque at the 2500-3500rpm range. This was still OK in 2nd and 3rd gear as the car does not have the rev range to build the torque, however in 4th gear and up if full throttle was requested at lower than 3500rpm the flywheel would reach its limit and start knocking/vibrating as the springs passed their max rate. If you drive the car at higher revs so as not to use the torque the standard dual mass will be sufficient. However you cannot use the torque these engines produce which is pointless IMO as this is where they build their power. At this point (no engine modification- only a de-cat) a DMF is ok, do not go for a solid flywheel!



As time went on I proceeded to add an uprated intercooler, M57N2 Turbo and exhaust manifold, 3inch straight through exhaust, egr delete and polybushed the full rear of the car, centre bearing and gearbox mounts. I then went for another remap, this time to the maximum I could produce with the stock injectors which should be c. 315-330bhp. At this point (145,000 miles) the dual mass flywheel (around 2.5-3 years old) was starting the make a faint knocking noise and the clutch was starting the slip in 4th gear up when using full power at 2000rpm. Within the next 5,000 miles the flywheel was starting to rattle and the clutch was only holding in 1st and 2nd gear.



What you need to understand is the car had lost most of the soft, comfy character as in order to control the power the drivetrain from the gearbox back was held with polyurethane (custom made 93A units). You can hear the diff whining slightly through the bushes, the road noise increased and so too did the road surface noise as the rubber which normally absorbs this was replaced with polyurethane. What I am trying to say is at this point in order to handle the torque, you need to sacrifice the comfort side of the car. For me the car handles well and is still comfortable for what I want (a set of budget coilovers would be alot worse).



At this point you need to decide what route you want to take. My DMF lasted 5,000 miles before the clutch would slip at any sort of torque in more or less every gear. When I removed the DMF the rubber in the centre had melted due to the vibrations, covered the flywheel and bell housing in rubber crap and the DMF had alot of in/out play. As far as I can tell this vibration and rubber paste was making the clutch slip.



You can do either of the below:



1: Reduce the power to the 280 bhp mark and drive the car using bhp (higher revs) which is really not ideal as the std turbo and exhaust choke the engine above 3500rpm



or



2: Go down the solid flywheel route and go for 400 bhp.



I went for option 2 as the loss of comfort does not concern me and the adrenaline rush received by so much torque is totally worth it. I did some research which I will detail below:



Uprated DMF - Ideally a DMF with stronger springs is the way to go. Basically when you apply power the engine side of the DMF will move, pull on the springs which in turn rotates to gearbox side of the DMF. When too much torque is applied the springs become fully extended before the gearbox side of the DMF has caught up with the engine side and the rubber which connects the two sides together vibrate. Stronger springs should allow the gearbox side of the DMF catch the engine side before they are fully extended. I asked many, many companies on the Web and this is not a service available (that I could find).



Light-weight DMF - I was going down this route as I have plenty of experience of these on S52 and S54 engines (made by the same company who made my kit). However the company who makes them advised not to go down this route in a daily car as the light-weight smf and solid clutch he used on his own 330Cd was far too noisy and harsh. For a track car it is excellent however as a daily car it is not suitable.



DMF to SMF conversion - Simply put you take a DMF, remove the rubber and springs and weld both sides together to make 1 solid disc. You still maintain the weight of the DMF and this weight is suppose to reduce the noise made by the gearbox when idling. I sent over an old DMF, Clutch and pressure plate and received back the DMF welded and balanced, the sprung clutch with a new type of clutch compound (tested to 800nm) and new pressure plate.



The results are as follows:



Gearbox chatter - I was expecting this. My gear box has about 10-15 degrees of "slap" when on the ground and you can hear the gears chatter. When connected to the engine this noise is amplified and to be honest is very noticeable from outside and inside to car. ie when at traffic light you get plenty of people turning around to see what the hell is making the noise (sounds alot like a truck). This is can eliminated by pressing the clutch however with the new pressure plate the clutch is a little stronger and I was advised not to do this so I let the gearbox chatter away. FYI I was at 155,000 miles on the origin BMW gearbox oil. I am using a heavier oil which reduced the nose considerably. FYI at 155,000 miles the original oil looked like crap!!!! I would advise changing your oil as this could have some relation to the slap my gearbox has (this slap may the completely normal, I do not have enough experience to say if it is normal or not).

Low Rev Range Vibrations - This is the biggest fall back of the SMF which I was not expecting. I potter around driving like an old man in 6th gear at 1,000rpm. Not anymore. In 3rd gear up you need to keep the revs no lower than 1,700-2,000rpm as the vibrations are awful. So much so that I am afraid the floor (soon to be reinforced) will fall out. Keep in mind a have semi-solid polyurethane gearbox mounted and a polyurethane centre bearing. I had a go at lining up the drive train and improved the vibrations however It needs to be 100% perfect to have no vibrations which is very difficult to do. If you have OEM gearbox mounts and centre bearing it might be ok, however I cannot comment. After 1 week of SMF driving my driving style has changed (drive around at 2,000rpm) and I have no issues with drive train vibrations. However just be aware town driving or carpark driving at low revs in 1st and 2nd is going the chatter and is not silent.



Power Delivery (the good part)- This is fantastic. I can use any gear at any revs and get no flywheel vibration and no clutch slip. Even with the DMF at full power higher up in the rev range (so no vibrations) I could feel it moving slightly and the gears felt sort of rough. With the SMF it is completely smooth, even the gear stick feels solid. Furthermore the gear change is instant and solid. I always felt the DMF twist (which is what is it suppose to do) when I changed gear and when on/off the power. That is gone and changing gears is a real pleasure now. However I do notice the play in the propshaf, diff, gearbox and halfshafts more now.





To recap:

1: 250bhp - Stay with a DMF, no modifications required



2: 280bhp - Keep the DMF, I would advise you poly bush the rear subframe and diff (7 bushes in total). You will need to use higher rpms in 4th gear and up so as not to damage the DMF.



3: 300-330bhp - At this point you have some turbo modification, exhaust and intercooler modification and most likely has alot of poly bushes. Again you can still use a DMF however higher rpm in a must in 3rd gear and up and be ready to replace the DMF and Clutch every 30,000 miles. IMO this is pointless as you really want to experience the 2,500rpm torque delivery which a DMF and std clutch will not hold.



4: 330bhp+ - Solid Flywheel is a must. I would advise against a light weight flywheel and go for a DMF conversion. My 800nm kit cost me £550 + and old kit for the conversion. This was the best bang for buck. The welding on the flywheel does not look pretty, however nobody is going to see it and as long as it does the job I dont care.This guy made a clutch and flywheel for a 330Cd which will do a quarter mile in under 12 seconds so I have complete faith in him. With this set-up I can experience the full torque these engine can deliver without worrying about the DMF and it is a completely new car.



By the way when driving at normal speeds(say at 60mph in the country or 75mph on the motorway) at around 2,000rpm the car fells even better than a DMF. No vibrations and nice smooth gear changes (also no downshifting anymore to overtake).



I hope the above explains enough. I will add pictures and a video later. If you are interested in a kit let me know as the garage I use said they can stock 1 or 2 kits if there is interest.



Thanks for reading, and if you have any questions let me know and I will do my best to answer them.