Most of you know us from the S54 side — the crankshaft journal-widening kits, rod bearing work, SMG conversions. We recently finished our first full S58 build (the new G80/G82 M3/M4 engine) and I figured this crowd would appreciate seeing what BMW's newest six looks like from the same bench the S54s cross, with all the measurements.
Background: customer's G80 M3, weekend/track car, barely 5,000 miles. Stock internals, tuned well past factory output with an aftermarket port injection kit. The bottom end let go on the street — rod through the block. We haven't finished tearing down the failed engine yet, so I'm not claiming a definitive root cause; I'll post what we find when it comes apart. Goal for the replacement was 800+hp capability.
The core
Good low-mileage S58 cores are hard to find for a platform this new — sourcing took longer than the bench work. Full teardown, every bearing inspected, crank magnafluxed (no repairs needed). One teardown find worth sharing: cleaning up one of the stock pistons revealed a hairline fracture near the second ring land that was invisible under the carbon. We've seen a similar failure pattern on a B58.
Every bearing shell indexed in firing order in 3D-printed trays so nothing gets transposed during measurement.
The build
Measurements — targets vs. what we achieved
This is the part I think is most useful to anyone considering a build, so here's the actual data. Everything below gets written into a build record that stays on file for the life of the engine — this one runs fifteen pages.
On that last point: whenever a build uses a new piston spec, we verify compression ratio from measured volumes rather than running the published number. Worth doing on any fresh combination.
S58 vs S54/S55 from the bench
This is the part I found most interesting given how much time we've spent inside S54s. Hold an S58 rod next to an S54 rod and the difference is immediate — the big end and bearing surface are dramatically wider. Twenty years of us widening S54 journals to buy bearing surface area, and BMW finally just designed it in from the factory. The timing gear teeth are machined into the crank itself, so the S55 crank hub issue doesn't exist on this engine. There's an integrated girdle across the mains tied into the oil pickup, and the VANOS drive is lighter than the S55's. Whatever you think of the modern cars, this is a very well-engineered bottom end.
Break-in and handback
Break-in was done on the road: progressive heat cycles, strict throttle discipline in the early hours, inspection between cycles. The car went back to the owner on a completely stock calibration with the port injection removed — a proven, leak-free engine on a known tune, so the owner's tuner can build power on a foundation that's been measured at every step. The owner shipped the car in from out of state and flew out to pick it up.
Full write-up with the build record sample: Building an 800+ HP S58, Start to Finish
Happy to get into clearances, measurement methods, or parts selection if anyone has questions.
Background: customer's G80 M3, weekend/track car, barely 5,000 miles. Stock internals, tuned well past factory output with an aftermarket port injection kit. The bottom end let go on the street — rod through the block. We haven't finished tearing down the failed engine yet, so I'm not claiming a definitive root cause; I'll post what we find when it comes apart. Goal for the replacement was 800+hp capability.
The core
Good low-mileage S58 cores are hard to find for a platform this new — sourcing took longer than the bench work. Full teardown, every bearing inspected, crank magnafluxed (no repairs needed). One teardown find worth sharing: cleaning up one of the stock pistons revealed a hairline fracture near the second ring land that was invisible under the carbon. We've seen a similar failure pattern on a B58.
Every bearing shell indexed in firing order in 3D-printed trays so nothing gets transposed during measurement.
The build
- Sleeved block — cylinder strength plus freedom on piston choice
- Copper O-rings machined into the block + ARP head studs — head seal under sustained boost. Combustion leakage past the gasket is a failure mode we've seen more than once on pushed S55s
- CP-Carrillo forged pistons and rods, ring lands and skirts spec'd for this application
- 8.9:1 compression — measured, not taken from the piston spec sheet (more below)
- Stage 1 cylinder head, rebuilt to spec — no porting needed for this combination
- OEM sealing throughout — the S58 relies on silicone sealing in a lot of places and we source those parts through BMW
Measurements — targets vs. what we achieved
This is the part I think is most useful to anyone considering a build, so here's the actual data. Everything below gets written into a build record that stays on file for the life of the engine — this one runs fifteen pages.
- Piston-to-wall clearance: target 0.0032" — achieved 0.00305–0.00315" across all six cylinders
- Ring end gaps (forced-induction spec): top 0.019", second 0.023" — filed and individually verified per cylinder
- Oil rail tension: measured three times per cylinder and averaged — 10.3–11.8 lbs
- Main bearing clearance: 0.0023–0.0028" across all seven journals, clearance set per journal, not per set
- Crank runout: under 0.0005" — end play: 0.007" (acceptance 0.005–0.010")
- Rod bolt stretch: relaxed length, stretched length, torque and angle recorded for all twelve bolts — 0.0065–0.0073" against a 0.0065–0.0075" window
- Wristpin clearance: 0.0012–0.002", checked to the rod and to the piston at every position
- Squish (piston-to-head): 0.042" all six (0.038" minimum acceptable)
- Compression ratio: 8.93:1 — chamber and piston dish volumes physically measured with liquid
On that last point: whenever a build uses a new piston spec, we verify compression ratio from measured volumes rather than running the published number. Worth doing on any fresh combination.
S58 vs S54/S55 from the bench
This is the part I found most interesting given how much time we've spent inside S54s. Hold an S58 rod next to an S54 rod and the difference is immediate — the big end and bearing surface are dramatically wider. Twenty years of us widening S54 journals to buy bearing surface area, and BMW finally just designed it in from the factory. The timing gear teeth are machined into the crank itself, so the S55 crank hub issue doesn't exist on this engine. There's an integrated girdle across the mains tied into the oil pickup, and the VANOS drive is lighter than the S55's. Whatever you think of the modern cars, this is a very well-engineered bottom end.
Break-in and handback
Break-in was done on the road: progressive heat cycles, strict throttle discipline in the early hours, inspection between cycles. The car went back to the owner on a completely stock calibration with the port injection removed — a proven, leak-free engine on a known tune, so the owner's tuner can build power on a foundation that's been measured at every step. The owner shipped the car in from out of state and flew out to pick it up.
Full write-up with the build record sample: Building an 800+ HP S58, Start to Finish
Happy to get into clearances, measurement methods, or parts selection if anyone has questions.