S6-37 6mt swap info (broken off from junk yard thread)

[discoelk]

This will be my last post on this topic but I am truly baffled why anyone would do this swap if their current gearbox is in good shape. For a SMG conversion, it makes sense if you find a cheap ZF.

The improved "shift feel" between the two gearboxes will largely be determined by the replacement transmission's treatment with a prior owner and there are so many variables that effect feel that its impossible to compare the ZF and 420g back to back. Because of this, the shift comparisons from Z4/zhp/e46m are a little meaningless imo. Having owned both transmissions, neither is going to be Honda levels of great but they're both nice with all new parts and some delrin carrier bushings.

The gear ratios are basically identical. No way you're going to notice 50 or 100rpm when driving.

[heinzboehmer]

Hi,

I actually love pedantic people because that is the only one way
to go further ahead and improve and mostly understand.

I did not wanted to go into deeper details but I have to now.

Note: I mentioned in my previous post that I can calculate
so called effective final drive ratio.

But in more simple language for those who does not know
how to calculate.

In order to calculate the effective final drive ratio one
needs to take the gear ratio and multiply by the differential.

SG6 4.35x3.62=15.747 effective final drive.
G420 4.23x3.62=15.312 effective final drive

The chart you post is fine but because the curves are not
very clear vs speed vs rpm and it makes it little bit confusing
not as clear as the chart bellow. I made very nice excel charts
so I can see things in close details when I calculate tires size,
vs HP vs TQ vs RPM vs Speed etc.
It's like dyno-chart if you print the chart to show the HP vs RPM
in say 20rpms increment vs a curve.

In the chart I made for us here pay attention on the speed
vs rpm vs RPM drop vs TQ vs speed.

So now if you look at the HP chart vs the SG6 rpm drop then
you will see loss of HP not by much but S54 needs every single
hp and tq in the world.

Something to suggest when you compare setup it does not
matter what it is you need to be fair and measure the rest to be
the same, in this case will be use the same tires size for both
gear box comparison. Because if you tweak one you can tweak
the other as well.


The rpm drop from from 1st to 2nd will affect the HP with around +/5-RWHP
and that is +/-9hp at the crank I can make the chart even closer to each other
but its a lot of work..the point I am making I think its understood.


I agree whit you, this is very small detail which will not be noticed day to day
driving but 0-60mph selling nonsense it does make a visual difference
if its 5sec vs 4.8sec its a window sticker mind game...back in the year of 2000.

(If anybody wants help with the differential gear ratio for the track, or tire size
let me know I will apply the data and reply)


Regards,
Anri

Yep, fair enough. The jump from 1st to 2nd is likely going to be noticeable compared to the 420G. Can't say how much without actually feeling it though. I need to drive a Z4M before fully committing to this swap, but the math has me pretty convinced.

And good point on the graphs. I posted pictures because I figured it was the easiest way to share. In the spreadsheet I made, I calculated speeds at 10 rpm increments so that you can mouse over the graphs and look at the numbers that correspond to each. Here's a link to a read only version (make a copy if you want to mess with it) of the spreadsheet in case anyone wants it: https://docs.google.com/spreadsheets...it?usp=sharing

[Anri]

Hill,

E34M5 3.8 is rated at 340hp DiN
E46M3 CSL is rated 360DiN
20hp at peak revs is not that much
off.

Now, take a look how BMW Engineers
re-design the S65 6 speed gear box.

This is because the power grew and
also the Torque curve is more in the
lower revs compared to E46M3 (stock
for stock)

Boy that gear box is as heavy as the
S54 alone...

Ratios are also changed vs G420.

Regards
Anri

[George Hill]

I have an 8spd with a 4.44 diff soooo why would I want to drive that diesel 3.23 ratio, lol.

My point was it seems silly to think that an engineer in 2002 (ish) would be like "you know what, I want to use this clunky transmission that was designed in the early 90s but BMW is making me use this superior shifting quality transmission that was just developed."

Everything is a trade off, time marches on and technology progresses.

[Anri]

Hill,

G420, G260, G560, G280, SG6, list goes on and on.

Gear box ratios are design for the given package and need.

- 0-60mph (nonsense) but sells the car.
-Curb weight
-Engine power hp v tq
-Engine RPM
-Fuel economy (little bit)
-6spd gives the opportunity to play with rear end much more than 5spd
for example E34M5 6spd uses 3.23 final drive. E34 540i uses the same
G420 but paired with 2.81 all based on all of the above.
- E31 850CSi used G560 with 2.93 final drive.
- E34 M30 535i used G260 pair with 3.46
- Overall package


Gear ratios, what's the purpose and the need ?

On my daily E28M5 I replaced the G280 with G260 paired with 2.56 rear end
from E36 325td Euro. On the freeway I am at 75mph with around 2100rpm..
just like Diesel Tractor

Go drive Euro E36M3 3.2 6spd Evo, soooooooo much better than E46M3
same gear box but the diff is 3.23 and paired with much stronger engine velocity in the
lower revs. Its also lighter by a bit.

Do you think that is the case or was it the 420g was designed in the 90s and they kept using it because it was a known concept but then time marched on and a better option was had (S6-37) and they started implementing it (E46 330i) before mass adoption and the 420g was phased out?

Also the input shaft is different on the V8 420g as well (just in case someone was thinking about trying to change the BH between the two).

Hill, never forget when BMW Engineers design a part for specific model they do it
so called Factor1-2-3-4...that meant that the part will withstand 1, 2, 3 times more than
the intended purpose is all based on "we want to make sure the part will not break at all
cost" BMW 188mm diff can hold waaaaaay more power than the gutless S54 can ever make..
but BMW put 210mm. E34M5 on boost the 210mm can hold min 700rwhp/TQ+. (Not on
drag strips with glue on the ground..)

I forgot but is the SG6 input smaller than the G420 ?



Regards,
Anri

[George Hill]

Yep that definitely changes the calculus. George, I’m assuming you’ve already measured heights/offsets of using an s54 flywheel and it’s a no go with any combo of parts?

I have not, but you also have to deal with the ring gear location in regards to the starter. So say you find a combo of S54 flywheel with S6-53. Now your ring gear is further from the back of the engine and you would have to reengineer mounting the starter. To make that work you would likely have to weld the bell housing so you can bolt the starter right to the BH and also have to deal with clocking it correctly to properly engage the teeth. IMO the juice isn't worth the squeeze.

53 can be made to be nearly a direct bolt in if you use 330d parts (which incidentally are pretty much the same as the 37 parts). But I wasn't aware of the flywheel issue, that'd make things challenging unless there's some other clutch/flywheel combo that could be made to work.

Keep in mind the diesel engine/transmissions are 20* so if you bolt that trans to our engine it will be 10* of horizontal.

With regards to the 37BZ - for using the 330i variant, one thought I had was installing some sort of extension where the factory pilot bearing sits to bring it out to the 330 position. Using the 330's needle bearing style if size is an issue.

There is someone making any adapter to do just that but I'm not sure what the benefit is when a stock clutch is likely just as capable at holding stockish power.

Remember BMW engineers will never do anything without a concept they have in mind, otherwise they would have had the G420 on std 330i as well...make 1 gear box for all...

The G420 is also covering E39M5 as well only the bell is different.

Do you think that is the case or was it the 420g was designed in the 90s and they kept using it because it was a known concept but then time marched on and a better option was had (S6-37) and they started implementing it (E46 330i) before mass adoption and the 420g was phased out?

Also the input shaft is different on the V8 420g as well (just in case someone was thinking about trying to change the BH between the two).

[Anri]

And don't forget the 37BZ transmission was used with the Z4M - which is an S54 equipped car with a 3.62 final drive ratio and 255/40R18 tires.

Terra,

Remember BMW engineers will never do anything without
a concept they have in mind, otherwise they would have had
the G420 on std 330i as well...make 1 gear box for all, just like
Mercedes loves to do this trick. they use the same box from
1.8 S/C up to 2.0 up to 3.2 V6 S/C.

The G420 is also covering E39M5 only the bell is different.


WIth the rates of pricing and condition more important the G420
is going day by day this SG6 makes a lot of financial sense, for sure.

I have not checked yet but perhaps if order New from BMW it
will be cheaper than the G420.

Regards,
Anri

[Anri]

Not trying to be pedantic, so apologies in advance if this ends up coming out that way, but the ratios are multiplicative not additive.

Technically, an M3 with an S6-37BZ and a 3.62 diff will have the same final drive ratio in first gear as an identical M3 with a 420G and a 3.725 diff. Yes, not hugely different to the number you mentioned, but it's a 2.9% decrease in ratio vs a 3.3% decrease.

The difference between a 420G and an S6-37 is so small in 1st and 2nd that you can easily make it up with different tire sizes. At 2.5k rpm in 1st, you'll be going 12.7 mph with the 420G and 12.3 mph with the S6-37BZ.

You do raise a very valid point, but I guess what I'm trying to say is that in real life the difference should not be hugely noticeable.

And yes, 6th is a different story, but also not as dramatic as the graph I posted above makes it seem! To cruise at 80 mph with a 420G, you're looking at right around 3100 rpm. Same speed with the S6-37 is right around 3200 rpm. Noticeable difference, but not hugely so.

Also, worth keeping in mind that this is all dependent on tire size. All my calculations have been done with a 255/40R18 rear tire size (stock) and if you stay close to that tire diameter, the numbers should be very, very close. Tire diameters that differ significantly will change things.

Hi,

I actually love pedantic people because that is the only one way
to go further ahead and improve and mostly understand.

I did not wanted to go into deeper details but I have to now.

Note: I mentioned in my previous post that I can calculate
so called effective final drive ratio.

But in more simple language for those who does not know
how to calculate.

In order to calculate the effective final drive ratio one
needs to take the gear ratio and multiply by the differential.

SG6 4.35x3.62=15.747 effective final drive.
G420 4.23x3.62=15.312 effective final drive

The chart you post is fine but because the curves are not
very clear vs speed vs rpm and it makes it little bit confusing
not as clear as the chart bellow. I made very nice excel charts
so I can see things in close details when I calculate tires size,
vs HP vs TQ vs RPM vs Speed etc.
It's like dyno-chart if you print the chart to show the HP vs RPM
in say 20rpms increment vs a curve.

In the chart I made for us here pay attention on the speed
vs rpm vs RPM drop vs TQ vs speed.

So now if you look at the HP chart vs the SG6 rpm drop then
you will see loss of HP not by much but S54 needs every single
hp and tq in the world.

Something to suggest when you compare setup it does not
matter what it is you need to be fair and measure the rest to be
the same, in this case will be use the same tires size for both
gear box comparison. Because if you tweak one you can tweak
the other as well.


The rpm drop from from 1st to 2nd will affect the HP with around +/5-RWHP
and that is +/-9hp at the crank I can make the chart even closer to each other
but its a lot of work..the point I am making I think its understood.


I agree whit you, this is very small detail which will not be noticed day to day
driving but 0-60mph selling nonsense it does make a visual difference
if its 5sec vs 4.8sec its a window sticker mind game...back in the year of 2000.

(If anybody wants help with the differential gear ratio for the track, or tire size
let me know I will apply the data and reply)


Regards,
Anri

[terra]

And don't forget the 37BZ transmission was used with the Z4M - which is an S54 equipped car with a 3.62 final drive ratio and 255/40R18 tires.

[heinzboehmer]

Having first gear shorter by 12points will make the
std M3 3.62 differential act like its 3.74 ratio. when SG6-37BZ
is used in E46M3. (I can calculate the effective final drive
but let not go there)

Not trying to be pedantic, so apologies in advance if this ends up coming out that way, but the ratios are multiplicative not additive.

Technically, an M3 with an S6-37BZ and a 3.62 diff will have the same final drive ratio in first gear as an identical M3 with a 420G and a 3.725 diff. Yes, not hugely different to the number you mentioned, but it's a 2.9% decrease in ratio vs a 3.3% decrease.

The difference between a 420G and an S6-37 is so small in 1st and 2nd that you can easily make it up with different tire sizes. At 2.5k rpm in 1st, you'll be going 12.7 mph with the 420G and 12.3 mph with the S6-37BZ.

You do raise a very valid point, but I guess what I'm trying to say is that in real life the difference should not be hugely noticeable.

And yes, 6th is a different story, but also not as dramatic as the graph I posted above makes it seem! To cruise at 80 mph with a 420G, you're looking at right around 3100 rpm. Same speed with the S6-37 is right around 3200 rpm. Noticeable difference, but not hugely so.

Also, worth keeping in mind that this is all dependent on tire size. All my calculations have been done with a 255/40R18 rear tire size (stock) and if you stay close to that tire diameter, the numbers should be very, very close. Tire diameters that differ significantly will change things.

[Anri]

Hi,

Something important to note.

The SG-37BZ has the following ratios.

1st - 4.35
2nd -2.50
3rd -1.66
4th - 1.23
5th -1
6th- 0.85


S54-G420

1st- 4.23
2nd -2.53
3th -1.66
4th - 1.23
5th- 1
6th-0.83


Having first gear shorter by 12points will make the
std M3 3.62 differential act like its 3.74 ratio. when SG6-37BZ
is used in E46M3. (I can calculate the effective final drive
but let's not go there)

For sure the gap between 1st and 2nd is larger and the
RPM drop will be higher than the G420. That is not that
much of a problem on M54-ZHP with disa-valve small intake
hi velocity etc..3.07-ZHP final drive, small duration cams, flat
tappet mushi M50 hydro lifters from 1989 E34, max revs is
6800rpm

Its not that its not going to work, I am just pointing the
Engineering went behind between the 2 boxes from this
point of view.


These boxes are very affordable.



Regards,
Anri

[terra]

That and its nearly a direct bolt in. 100% the way to go unless you are making a bunch more power over stock IMO.

53 can be made to be nearly a direct bolt in if you use 330d parts (which incidentally are pretty much the same as the 37 parts). But I wasn't aware of the flywheel issue, that'd make things challenging unless there's some other clutch/flywheel combo that could be made to work.

With regards to the 37BZ - for using the 330i variant, one thought I had was installing some sort of extension where the factory pilot bearing sits to bring it out to the 330 position. Using the 330's needle bearing style if size is an issue.

[heinzboehmer]

On the plus side, S6-37 gear ratios are super close to the 420G, so no diff swap needed. Only meaningful difference is a shorter sixth, but that's okay.

I'll post the comparison graph when I'm back at my computer

Edit:

Here's 420G vs S6-37, all else equal:



Totally agree with George Hill. This seems like the one to go with.

[Bry5on]

Yep that definitely changes the calculus. George, I’m assuming you’ve already measured heights/offsets of using an s54 flywheel and it’s a no go with any combo of parts?

[George Hill]

Really makes the S6-37 much more appealing now.

That and its nearly a direct bolt in. 100% the way to go unless you are making a bunch more power over stock IMO.