[BryanM]

Have done all the threads on 3.6 clutch and flywheel on 3.8 engine and particularly thought Farrells on his engine balance/ crankshaft damper ideas very informative. I still like the idea of going ahead with it as we have a very light flywheel and paddle clutch on a Reliant GTE we have, and it transformed the car losing 14lbs off the assembly and totally sharpens the Essex V6 engine although this was professionally built and all the relevent parts were balanced both individually and as an assembly.

My question is simple however, has anyone done the conversion who would be hard on their engine ie. sprints, Nurburgring or trackdays etc. or had an engine blow up as a result of this mod? I have already lost a 3.6 engine at a sprint, although it had been chipped before we got it, and wouldn't like to blow another one up. Although my son and I use the cars hard (see youtube 'david mutch' or 'bryan mutch'), we don't generally have engine problems as they are 'built for purpose' but I don't want to ruin a very good and quick car with a mod i'm not 100% sure of.

 

[davidoli]

Hi Bryan ,

Your thread , a slipping clutch and a lovely 4.5 kilo single mass flywheel sitting in my workshop , were all contributory factors in my decision to fit a lightened flywheel to my 3.8 M5 today .

The original dual mass flywheel weighs appx 14 kilos :

My lightened version weighs 4.5 kilo :

I removed the exhaust , prop , gearbox , clutch and dual mass flywheel and offered up the new flywheel , only to discover that I only had 3.8 flywheel bolts on hand which are obviously too long :

A thorough hunt around and thankfully I managed to find a set of the 3.6 flywheel bolts which allowed me to get everything bolted up today . Big thanks to FinalEdition for his assistance in lifting the 55 kilo exhaust back onto the M5 ....... Much easier with 2 pairs of hands !

Apart from the throttle cable deciding to snap as I demonstrated how much quicker she now revs , everything went extremely well and I was amazed at how freely she spins up now , pulling through the gears with far more urgency and feeling electrifying when she comes on cam !

I have only driven a few miles home on treacherous country roads and will update further in due course , although I am very pleased with my initial experiences .

I also have a 2.8 kilo variant which will be fitted to a customer's M5 in the near future , updates to follow :

D

 

[First e28 M5]

davidoli,

Where did you get that flywheel maaaan :grrrrr: only 2.8kg....That 3.8 will rev like a madaaaa fukaaaa :checkeredflag: I have the UUC and I am very happy.

Anri

 

[davidoli]

We have a fantastic Engineering Co local to us that is currently making them to order .

I brought them a standard 3.6 SMF and their lightened design was based on that . The flywheel that I have fitted to B7 TAP was actually ordered for a customer that we are carrying out an engine rebuild for , but I decided to fit it as we are still awaiting other parts for his build !

When I showed him the flywheel , he asked if it were possible to have a new gearbox with a transparent bell housing !

D

 

[BryanM]

Does your engineering company need a 3.6 flywheel to start with or do they now have a pattern to allow them to make copies and if so how much are they roughly? An obvious question but I presume the 3.8 flywheel bolts have a deeper shoulder and so simply cutting a bit off the length doesn't do the trick? This has turned from a 'want to do', to a 'need to do'.

 

[davidoli]

Hi Bryan , they now have the template to run off a batch upon request .

The 3.8 bolts are too long , with the thread towards the end of the bolt , so cutting them down is not an option .

The 3.6 bolts are only 22mm long and I have a set arriving from BMW tomorrow ( not cheap ) which I will see if I can have made also .

Believe me when I tell you , the improved responsiveness of my car and sheer feeling of increased power delivery is phenomenal !

D

 

[Gerg]

You just helped me decide which way to go with my slipping 3.8 clutch.

 

[davidoli]

You just helped me decide which way to go with my slipping 3.8 clutch.

That is exactly what preempted my decision Greg .

My clutch started slipping and I had the parts on hand , so it was the perfect opportunity and the transformation is incredible for such a relatively straightforward modification .

There appears to be very little ' rattle ' and the clutch pedal feels just as light as before . There is a touch more noise when the clutch pedal is depressed with a stock OEM 3.6 clutch plate .

Gear changes are smooth and trouble free .

D

 

[e28s38b36]

Hi Bryan , they now have the template to run off a batch upon request .

The 3.8 bolts are too long , with the thread towards the end of the bolt , so cutting them down is not an option .

The 3.6 bolts are only 22mm long and I have a set arriving from BMW tomorrow ( not cheap ) which I will see if I can have made also .

Believe me when I tell you , the improved responsiveness of my car and sheer feeling of increased power delivery is phenomenal !

D

Whats the damage for the super light flywheel D? Wouldn't mind having my 3.6 spin up a little quicker. :biggrin:
Got to fit my 6 speed once it has had it's new casing anyway so may as well fit the flywheel at the same time.

How much were the 3.6 flywheel bolts from BMW? Makes sense to fit new ones at the same time.

 

[pspassos]

who wants to buy a 3.8 OEM flywheel with 6k km on the clock, toguether with the clutch, and a spare clutch kit (came two in the set, dont know why)?
I can give it as payment for a lightweight one....

and that 2.8kg.... ow my god.... must be stunning!

 

[davidoli]

Hi Shaun ,

I thought you might like one of the crazy , nutta , 2.8kg versions which are appx £395 , although I may be able to negotiate a discount if I order a few .

The 4.5kg version is £345 which is remarkable when you consider that a standard 3.6 flywheel is appx £530 if available .

The 3.6 bolt price will have to be confirmed as I am still awaiting delivery from BMW , despite being assured that I would have them 2 days ago .

D

 

[EddyDevelopments]

Arent you guys scared of some major engine damage with those feather light FW ?
In worst case scenario, the crankshaft gets broken.
Im all go for tuning, but if you lighten one component at one side of the engine, then you have to lighten up the front balancer to.
And on top of that get the whole thing balanced...

 

[e28s38b36]

Hi Shaun ,

I thought you might like one of the crazy , nutta , 2.8kg versions which are appx £395 , although I may be able to negotiate a discount if I order a few .

The 4.5kg version is £345 which is remarkable when you consider that a standard 3.6 flywheel is appx £530 if available .

The 3.6 bolt price will have to be confirmed as I am still awaiting delivery from BMW , despite being assured that I would have them 2 days ago .

D

Thanks D. Sounds good to me. :M5thumbs: Have you weighed a standard 3.6 flywheel?

 

[e28s38b36]

Arent you guys scared of some major engine damage with those feather light FW ?
In worst case scenario, the crankshaft gets broken.
Im all go for tuning, but if you lighten one component at one side of the engine, then you have to lighten up the front balancer to.
And on top of that get the whole thing balanced...

3.6 flywheel on a 3.8 is a well documented mod.

My own car will be having lighter pistons, conrods etc & will be blue printed along with the lighter flywheel. Should rev like a bike engine! :biggrin:

 

[davidoli]

Hi Shaun ,

Standard 3.6 flywheel weighs 5.74kg

EddyDevelopments , No I am not worried ........ our flywheels are balanced and our engineers confident that there will be no issues .

D

 

[farrell]

Arent you guys scared of some major engine damage with those feather light FW ?
In worst case scenario, the crankshaft gets broken.
Im all go for tuning, but if you lighten one component at one side of the engine, then you have to lighten up the front balancer to.
And on top of that get the whole thing balanced...

I've been asked to post on this subject.
I doubt you would find much arguement from Paul Rosche whom we spoke with at length with on this subject in 2009.
Along with camshafts, crankshaft resonance is a pet subject of his.

A single balanced component however well made, does not balance a reciprocating mass of assembled parts.
And, the only way you can test the results of your meddling is on an engine dyno or wait for the bang !

Theres less margin for error in an engine with a long crankshaft that revs past 7000 rpm.
Yes, there will be less intertial mass. Yes, it will feel quicker on tip in / tip out , but with more vibration & defined
change to 1st & 2nd order modal frequency peaks. A different configuration engine such as flat 4 or V6 may not incur such a problem.

For the S38 & other high output long crank straight engines, the requirement is to maintain durability. Reducing weight in isolation
of addressing balance can be just like raising the engine rpm limit to a point of destructive coincidence. It's a risk to consider.
This may be acceptable practice (risk assessment) for a race engine where engine teardown is a regular occurance,
but even BMW motorsport have got this wrong in the past.

Someone mentioned 3.6 to 3.8 flywheel change as an upgrade to B38 engine. If it was such an upgrade, why did BMW not use
the B36 flywheel or the B36 mass damper for the B38 ?

I'm building a naturally aspirated 400 bhp S38 B38.
I can assure you that it does not require zillion degree duration camshafts & other Halfords branded parts to succeed.
I could be wrong. Doubt Paul Rosche is though !

Cheerio.

 

[First e28 M5]

Farell,

Very good point and well said... The only one way to prove that durability to all of us to find out is "Time will tell" when some one with 3.6 or 3.8 install this 2.8kg FW and drive lots of track time this will be the 100% test to see if this is working or NOT. Until that moment only guesses and theory will be said as opinions.

The 3.8 FW upgraded to single mass FW from 3.6 is done many many years ago and I have not heart one failure to the crank shaft what so ever since this upgrade started, did you ?

You mentioned if the upgrade is so great why BMW never put the 3.6 FW to 3.8 FW. 100% one of the reasons is the comfort drive, smoothness. You know very well how jerky is to drive the E34 M5 3.6 ! you jump to drive 3.8 smooth off the line and relaxed. That actually proves the that because. Neither of S50-B30/B32, US-S50/S52. S54-B32, S62/B50, S65-B40, S85-B50 engines came with single mass flywheel!

Only, S38-B35, M88/3, M88/1 S38-B36, S14-B23/B25 all came with single FW. I believe on this final edition S38-B38 3.8 BMW had some of the NEW Generation goodies!, Coil on plugs, different DME, dual mass FW, Cam shaft position sensor,V-Max box 250km/h, they all came from Euro S50 which was already in production along with B38 3.8.

Farrel, you know members hear Jari "Camber", and Janne MM-5. Jari he uses Alcon 4.5kg FW on his B38 3.8. My opinion is this guy I would say is the Guru on the S38 engine build and hands down on him! We all talk hear with theory tra lalalaa. He does experiment all that on the track! He had so many hours on the race track with that Alcon 4.5 FW that you and I dont have many hairs on out heads. He never had any problems damaging the 3.8 crank shaft what so ever from using light weight FW.

I remember few years ago when some company made light weight pulleys for S50.. and Steve Dinan proved that this will damage the crank shaft with no time ! He never said a word about to upgrade 3.6 single FW to 3.8..

My personal opinion is to go to extreme is not good so the golden middle range works allays safe. 3.6 to 3.8 is proven through the years.

If You and Paul Rosche you guys doubt the 2.8kg as durability use the 3.6 something proven.

Just my 02 sents
Cheers
AnriI

 

[EddyDevelopments]

I've been asked to post on this subject.
I doubt you would find much arguement from Paul Rosche whom we spoke with at length with on this subject in 2009.
Along with camshafts, crankshaft resonance is a pet subject of his.

A single balanced component however well made, does not balance a reciprocating mass of assembled parts.
And, the only way you can test the results of your meddling is on an engine dyno or wait for the bang !

Theres less margin for error in an engine with a long crankshaft that revs past 7000 rpm.
Yes, there will be less intertial mass. Yes, it will feel quicker on tip in / tip out , but with more vibration & defined
change to 1st & 2nd order modal frequency peaks. A different configuration engine such as flat 4 or V6 may not incur such a problem.

For the S38 & other high output long crank straight engines, the requirement is to maintain durability. Reducing weight in isolation
of addressing balance can be just like raising the engine rpm limit to a point of destructive coincidence. It's a risk to consider.
This may be acceptable practice (risk assessment) for a race engine where engine teardown is a regular occurance,
but even BMW motorsport have got this wrong in the past.

Someone mentioned 3.6 to 3.8 flywheel change as an upgrade to B38 engine. If it was such an upgrade, why did BMW not use
the B36 flywheel or the B36 mass damper for the B38 ?

I'm building a naturally aspirated 400 bhp S38 B38.
I can assure you that it does not require zillion degree duration camshafts & other Halfords branded parts to succeed.
I could be wrong. Doubt Paul Rosche is though !

Cheerio.

Theres nothing to say to this realy:M5thumbs:

 

[///Manuel]

From here:

Lightened Flywheel Lightened flywheels are the realm of drivers most dedicated to performance. The thing that should be stressed is that they are really not for cars driven on a daily basis. A lightened flywheel will produce more responsive shifting and engine rev’s as well as generally improved acceleration throughout the gears. That is because the rotating mass (or the amount of weight the engine has to move to speed up) is drastically reduced. However lightened flywheels reduce drivability under most circumstances. Cars with lightened flywheels are more apt to stall in traffic, are much noisier (clutch rattle or chatter) and will probably increase engine vibration (which can reduce engine life). For most drivers, a standard or slightly lightened single mass flywheel will give the biggest performance benefit without the trouble of a drastically lightened flywheel.

--------------------------------------------------------------------------------------------------

BMW didn't only increase weight and migrated to a dual-mass flywheel solely for engine durability, they also did it for a smoother clutch action and daily driving experience to please a wider range of customers. Unfortunately sometimes at the cost of performance and raw feel. This is even more true today than ever with the newer BMW's.

 

[Baddie]

Interesting debate.

As an example, the Porsche 997 GT3 has a dual mass flywheel, but the RS version does not. I have no experience of either car but the journalists describe the RS as a pain at low speed. I don't recall reading comments about dramatically improved response but perhaps we are meant to take that as read. But the thing about this flat-6 is that it has a) a short crankshaft that is far less prone to torsional vibration than that of a straight-6 and b) it has a much shorter stroke than the S38; so at any given engine speed crank reliability is much less of an issue in the short Porsche engine. (The reason the original E30 M3 had a straight four not a six was to keep the crank short and durable for 10,000 rpm racing).

The B38's dual mass flywheel may have been added for refinement and low speed manners, but it was designed into a new reciprocating system. There's little doubt a lightweight flywheel can be incorporated into a harmonised reciprocating system if you are prepared to sacrifice traffic manners, but would have concerns about changing only one element in the system. If I was not concerned about the risk of knocking a few thousand miles off the life of my crank then I would be keen to try a light flywheel, I'm sure it would be fun. Conversely, if for the sake of argument, the B38 had exactly the same crank rods and pistons as the B36 and the dual mass flywheel was only an add on, I would probably be one of the first to swap to single mass and put up with the traffic shunt. However I would like to do what I can to maximise the life of my engine so for me the risk is not worth the potential gains.

Incidentally the M1 Procars had problems at their first races with cranks snapping and they had to drop the rev limit until they got the torsional dampers right, showing how critical such a system is. Even the S70/2 V12 (with a featherweight aluminium flywheel) has a crank damper at the front of the crank to increase durability at the expense of some inertia. In the 20 years since that epic engine materials and analysis has moved on and cranks may be stiffer, as witness Audi building long stroke engines (at a time when BMW went to a shorter stroke) revving to over 8k rpm.

Off thread, has any one wondered if BMW's S1000RR sportsbike is the result of disaffected NA enthusiasts leaving the roadcar division? At their first go they produce an engine with 193 BHP/litre and upped the performance ante for all bikes :checkeredflag:. It's top-end allegedly bears some similarities to their F1 engines....