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

[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.

[heinzboehmer]

Made this its own thread, to unhide good info.

Nice, thanks for that

I was hoping that would be the case, but not so. The way the flexplate/flywheels are made they are "tuliped" around the the crank flange (if that makes sense). Actually here's a pic.

Damn that's a bummer. Really makes the S6-37 much more appealing now.

[Obioban]

Made this its own thread, to unhide good info.

[George Hill]

I'm glad you mentioned this, I had not even considered this. So the problem is that the flywheel interferes with access to those bolts? If it's just that the bell housing doesn't have holes in the correct spots, then that sounds like an easy fix

I was hoping that would be the case, but not so. The way the flexplate/flywheels are made they are "tuliped" around the the crank flange (if that makes sense). Actually here's a pic.

[heinzboehmer]

*If you bolt the N5x transmission straight to the block without a bell housing adapter you CANNOT take the oil pan off with the transmission installed. The way the flexplate/flywheel is designed you cannot access the oil pan bolts into the RMS.

I'm glad you mentioned this, I had not even considered this. So the problem is that the flywheel interferes with access to those bolts? If it's just that the bell housing doesn't have holes in the correct spots, then that sounds like an easy fix

[George Hill]

Keep in mind all the N5X transmission are not a straight swap onto an S(M)5x engines. Highlights that are likely most important to this group are:
*Starter - Starter bolts to the M/S5x transmission and to the engine on the N5x. I (HPB) make an adapter to bolt the starter to the transmission to solve this issue otherwise you need an adapter plate from Domiworks, Adamat or PMC.
*If you bolt the N5x transmission straight to the block without a bell housing adapter you CANNOT take the oil pan off with the transmission installed. The way the flexplate/flywheel is designed you cannot access the oil pan bolts into the RMS.

[heinzboehmer]

My understanding is it's close enough that it'll all bolt up. I think there is technically a 5mm difference or so, but there's enough slack in the CV to make up for that.

Not something I would bother with personally unless my 420g was dead. And if I were at that point, I'd probably also look into the GS6-45 and GS6-53 from the newer cars.

I have a ton of seat time with an S6-45 and that thing shifts awesome.

However, I've heard of multiple cases where people have experienced catastrophic synchro failure. Close friend of mine had the reverse synchro go in his car (same one I have a bunch of seat time in) and there's multiple reports of the same sort of thing online. Not trying to fearmonger or anything, but that transmission does seem to have a weak point. Think the S6-53 is the better choice.

https://f10.5post.com/forums/showthread.php?t=1672552

https://www.bimmerforums.co.uk/threads/2011-335i-manual-6-speed-broken-reverse-gear-gearbox-teardown-help.575461/

https://www.1addicts.com/forums/showthread.php?t=1382573

https://www.e90post.com/forums/showthread.php?t=1087237

[heinzboehmer]

I know this is a junkyard thread and not a transmission swap thread, but I did some math this morning and figured I'd share.

Here's the difference in rear wheel speed between the 420G and S6-53, all else equal:


Longer 1st-4th, same 5th and shorter 6th.

And here's the difference in rear wheel speed between a 420G with a 3.62 diff and a S6-53 with a 3.81 diff:


Pretty much identical 1st-3rd and shorter 4th-6th.

So, if you like the M3 factory gearing and want to swap in an S6-53, you should budget for a diff gearing change as well.