My 2¢ on the s54

[ForcedFirebird]

Never had the pleasure of breaking an s54 until recently. BMW made quite a few improvements, and got quite intuitive when it comes to keeping the engine short in nature.

The rods are the inferior snapped cap style, powder forgings obviously, yet very stout with the organic rounded I beam design. Powder is great for a strong rod, but they have catastrophic yield points. True forged rods in engines of yesterday that were machined apart are able to be reconditioned. Snapped caps area different animal. If the rod can be sheered so easily to break the cap off, the same thing will happen when it reaches yield.

Upon breaking two engines, the first thing noticed was they both had the rod bearings replaced with coated aftermarket shells. In both engines, the upper shells are wiped. Both engines are late model and have 11mm rod bolts.

Once the pistons came out, it was immediate apparent the piston pins are smaller diameter than the previous generations of the baby six. The rod crank pins are fatter, but this late baby six main bearings remain unchanged from previous generations.

The heads will be broken soon, and they will go on the flow bench. The ports look exceptional for a stock unit. Machined all the way through, no casting flash what so ever, the shape is direct. Very excited to analyze these.

That's all for now, just excited to share.

[ForcedFirebird]

Usually BMW would have the bottom of the piston meet the bottom of the bore (imagine "short skirt"), but the rod and stroke ratio of the s54 combined with the fat powder rods forced them to notch the bottoms of the cylinder bore for clearance. This will increase piston rocking and side load, yet the pistons on both engine appear to be in typical condition for ~100k mile baby sixes.

[ForcedFirebird]

To my surprise the pistons also have notches to accommodate the bob weights. Tisk tisk. An item BMW decided to include in an OEM build is exactly what I have been doing to the b28/130mmrod/OEM/m20 compression height piston combinations. Turning the crank down to accommodate piston skirts is NOT they way BMW went in this "millennial" baby six.

[ForcedFirebird]

s54 rods are 620gm +/- 1gm on engine one.

[ForcedFirebird]

Wrist pins went from 22mm to 20mm and went from 104 to 98gm.

EDIT:

Piston rings measured:

1.2mm top with a .25mm ring gap
1.5mm second ring, typical BMW Napier style, with a .62mm ring gap
2mm oil control ring with .5mm gap

Bore clearance (exact mileage unknown on this one) was increased from earlier engines from ~.02mm to .0028" (.7mm) minimum, this engine is still right at minimum spec.

Also noticed after an ultrasonic bath, the pistons are rocking in the bores. Excessive scuffing above the compression ring on the exhaust side (front exhaust valve relief especially). All pistons have the same marks.

[ForcedFirebird]

Pistons maintained weight at 498gm +/- 2gm from the m20 to s54.

[ForcedFirebird]

m20 rods are 620gm +/- 5gm

[ForcedFirebird]

Both s54 engines are destined for turbo applications. One is hoping to keep the head attached, the other is a thorough rebuild. It won't take much to pop the head off and open the ring gaps, but "the internet" says the s54 is good for boost, yet broken ring lands on "flat" quench pistons seem to be common unlike the m20 with it's stout top land (yes I am partial to the mighty m20).

EDIT:

So, customer #1 is Ok with o-rining the block. There is very little material left between the siamesed cylinder bores. 4mm OD to OD. We are going with a 1mm copper wire, OEM steel gasket, opening the ring gaps - will post measurements once we pinpoint ring type/material. The OEM compression ring is thin, but the ring lands are stout. Upon further inspection, the pistons may not be rocking as much as I originally thought - the valve reliefs being so close to the ring lands have me suspect. Appears excessive force being applied to this area.
__________________

[dude8383]

Interesting stuff here! I'm going to be tearing down my own S54 for a rebuild as well :)

[2mAn]

An item BMW decided to include in an OEM build is exactly what I have been doing to the b28/130mmrod/OEM/m20 compression height piston combinations.

Tell me more about this b28 combo, you can PM me so I dont derail this thread

back on topic, what is your overall impression of the S54?

[digger]

the s54 is one of the best NA engines ever produced and there is alot of performance potential

[DesertBMW]

S54 is made for 'naturally aspirated' application only. The whole intake, head and combustion chamber is designed for "NA scavenging effect" to get the best flow rate. If you compare it to N54, you will see that N54 has heavy duty pistons like diesel engine with deep centered dish. Valves are not that large, intake ports are not that large, intake manifold is short

[Wanganstyle]

My 2¢ on the s54

S54 is made for 'naturally aspirated' application only. The whole intake, head and combustion chamber is designed for "NA scavenging effect" to get the best flow rate. If you compare it to N54, you will see that N54 has heavy duty pistons like diesel engine with deep centered dish. Valves are not that large, intake ports are not that large, intake manifold is short

Just like a f20c; an s54 makes stupid power if you add a proper turbocharger setup. Both can make 1krwhp on stock parts in burst mode. Much less than that reliably

N54 is an engine with more than a host of its own issues (hpfp, carbon buildup, injectors failing, coils failing, oil filter stand leaking, turbines failing. Makes decent power boosted up but for how long is the real question ......a 500hp++ single turbo n54 also require building to stay alive; nothing is that easy to just fit junk parts to and make power


Turbocharging a 100hp/liter++ na engine always produces fantastic results if one has the budget and does things properly.

Those who re-use old piston rings would be very scared of turbocharging a high output NA engine.

[TobyB]

Those who re-use old piston rings would slap a turbo on that beyootch and crank the boost to 2.5 bar

The rest of us would be a bit timid about trying to shove a lot of extra air into something
as high strung as 100hp/liter and probably proceed with some caution...

heh

t

[ForcedFirebird]

First off, apologies for the format of multiple posts, but wanted to save a few for future findings. Always annoying to see "reserved" in multiple posts that never get updated, at least this way, there's something in those posts.

Second, I have found over the years (on multiple engines/makes) that if the engine is a great high effort engine, then adding boost produces exponential results. I have never been one to believe what I read, specially when it goes against common sense and experience.

If a head flows well for N/A, it will flow well for boost. Many have tit backward and think more boost means more power, but that's not always the case. Boost pressure is a byproduct of air that cannot be forced through the engine. If you take an engine with a turbo on it, then have the head professionally ported (with verified gains), power will go up, boost at the gauge will go down. Also, another misconception is that because you turn up the wick on your turbo, you will make more power. This is true as long as you selected a proper turbo and are not out of the efficiency map - otherwise you are creating more pressure and heat without the hp/psi gain ratio you would expect.

A final misconception of boost is that you are striving for zero cam overlap. I have not found this to be true. In theory, yes, "trap all the mass" seems the way to go, but even in boosted applications, overlap is not a bad thing (again, with a properly selected turbine). If you have a 2:1 exhaust to intake pressure ratio, either your manifold design is horrible, your gate is too small, or the most popular: the turbine that is too small in comparison to the compressor. You have to remember, whatever turbine you select needs to be able to flow the amount of gasses that your engine will produce at the desired HP level. All that being said, if you are under 1.5:1 boost pressure ratios, overlap on your cam is fine. Supersonic air speeds are not going to have time to change direction and revert to the intake tract due to some cam overlap. I bring up the cam overlap because we all know in the days of early 24v, everyone wanted to boost the m50NV since it had no variable timing, and kept the low overlap in comparison to vanos engines (as well as less engine management for stand alone systems).

Finally compression ratios. They don't scare me. As long as you have your timing and fueling in check, a higher compression engine with less boost will outrun the lower compression with higher boost (all else being equal). Sure, they both will delta near the same power (based on mechanical limits of the engine), but the higher compression engine will make more power before and coming into boost, need less pressure (boost) to make equal power, but you will have less "padding" during the tuning.

Now, enough of "Turbo 101", let's get back to the s54. :D