Advice needed

[Z4MCoupe86]

Looking to replace my rod bearings next year. I am also in the process of doing some upgrades to my car, and ultimately do a tune to compliment them.

One thing I've noticed is that the throttle limiter on z4m is much less aggressive than what is said to be used in the e46 m3 and csl. The limiter in place on the m3 is supposedly to help with torque, but I wonder if the z4m limiter is in place to help with rod bearing wear. See attached pics, as well as below link for reference.

One of the items I was hoping to do with my tune was to at a minimum reach parity with what the csl has /allows, including changing the limiter (if not removing it altogether). Before I do so, I want to ensure that I mitigate any incremental risk in doing so. Or at least understand why these values would be different between the two platforms.

So my questions are :

1) Are there any known reasons why these limiters would be different between the two platforms?

2) Is the m3 limiter in place to help with torque production, to provide mechanical sympathy to the drivetrain, or some other reason?

3) Assuming the z4m limiter is in place to assist with RB wear relative to the m3, would an oil pump that delivers more volume (as linked below) give me the technical right to remove the limiter while maintaining or improving reliability?

4) Are similar limiters in place on the s65 v8, and if yes, is the profile more like the z4m or e46 m3/csl?

Any insight or guidance here is greatly appreciated!

https://www.bimmerforums.com/forum/show ... lectronics

https://store.vacmotorsports.com/vac-mo ... p1033.aspx

[Argenta]

I only know the Siemens software as such is different, maybe something to do with that?

[Z4MCoupe86]

Not sure. I'm also operating under the assumption that the oil systems are the same between the platforms. Obviously mss70 is more advanced, but would rather I be more conservative in my approach as it pertains to this.

The below is also a bit of an interesting read on the matter. Just trying to piece this all together


https://bobistheoilguy.com/forums/threa ... es.279577/

[abar121]

It could be due to quite a number of factors, from keeping the intake velocity up at low revs, to matching the resonance of the exhaust. Or noise / emissions limitations, or for drivability etc etc.

[Z4MCoupe86]

I've reached out to vacmotorsports to try and get some insight on this. Lots of unknowns currently.

[Mikey_Boy]

This will either help or throw more fuel on the fire

Limiting throttle on the S54 engine has *nothing* to do with rod bearing wear. Maximum cylinder pressures are around max torque values (about 5000rpm-ish on the S54?). Max cylinder pressures naturally have a big effect on bearing wear - big impact on piston translates into big impact onto rod bearing. Limiting the throttle openings has everything to do with air speed to maximise torque and driveability.

Thrashing from cold will have more effect on rod bearing wear than torque limiting or oil pump spec. Bearing clearances are pretty tight on the S54 to minimise parasitic losses but that also means maintaining bearing film thickness is a challenge when the engine is cold. I’ve said this several times - S54 bearings are a touch too narrow - accept they are a service item every 50k miles, warm the car through properly before using high RPM or throttle load and you’ll be golden.

Oil pumps on S54s are pretty basic - volume goes up (to a point) with revs until the relief valve kicks in. You’d be surprised how much flow there is at idle and low revs. You could try to have variable flow against revs, but likely you’ll cabbage the engine’s requirements somewhere on the speed / load range. BMW likely spent a LOT of R&D cash getting the oil system as well sorted as they could for the S54.

I’d leave the oil system well alone, get your bearings done, get your engine mapped properly by a reputable S54 expert and use a high quality oil changed at more regular intervals than BMW recommend.

I’ll get my popcorn and wait to be shot down in flames….