Documented forum build · 997.1 · water-cooled
2008 997.1 Carrera 4S 4.1 upgrade
A preventive 3.8-to-4.1-litre Hartech rebuild with a published rolling-road result and owner follow-ups at 5,000 and 15,000 miles.
Evidence: Opening post · Documented work list · Reported rolling-road figures · 5,000-mile follow-up · 15,000-mile follow-up
- Vehicle
- 2008 Porsche 997.1 Carrera 4S Cabriolet
- Engine
- 3.8-litre 997.1 Carrera 4S flat six → 4.1-litre Hartech closed-deck flat six
- Forum
- 911UK
- Thread author
- drmark · 6 December 2022
Vehicle and engine evidence: Opening post · Cylinder findings · 4.1-litre decision · Documented work list
Why it came apart
A preventive rebuild was chosen despite no reported smoke or oil consumption; inspection was then reported to show moderate early bore scoring.
Source: Opening post · Cylinder findings
What the project aimed to do
Increase displacement and mid-range response while renewing the engine and ageing ancillaries.
Source: 4.1-litre decision · Mid-range response objective · Documented work list
Who did what
The owner documented the decision, specification, dyno results and mileage follow-up; Hartech performed the engine build.
Source: Complete 911UK thread · Documented work list · Reported rolling-road figures
Original 3.8-litre engine at a reported 67,000 miles; the exact engine code is not stated in the reviewed posts.
Vehicle context: Opening post · Cylinder findings
Documented sequence
Preventive strip and bore inspection
The opening posts record the preventive decision and the moderate bore scoring reportedly found after dismantling.
Source: Opening post · Cylinder findings
4.1-litre decision
The owner selected the 4.1-litre upgrade after discussing the available rebuild scopes.
Source: 4.1-litre decision
Engine and ancillary work
The thread lists the internal build, head work and the cooling, oiling, clutch and exhaust items renewed at the same time.
Source: Documented work list
Rolling-road measurement
The owner published the reported peak figures and a separate 3,000 rpm torque point after completion.
Source: Reported rolling-road figures · Reported torque at 3,000 rpm
Long-distance follow-up
Updates at 5,000 and 15,000 miles describe oil use, servicing and long-distance operation.
Source: 5,000-mile follow-up · 15,000-mile follow-up
Named components and work
4.1-litre closed-deck conversion
Six high-strength aluminium-alloy, nickel-silicon-plated, closed-deck wet liners with performance pistons and rings.
Source: Documented work list
Bottom end, timing and heads
Crankshaft and connecting-rod bearings, timing chains and guides, IMS work and reconditioned cylinder heads.
Source: Documented work list
Cooling, oiling and ancillaries
Low-temperature thermostat, water and oil pumps, oil cooler, air-oil separator, tandem pump, clutch, engine mounts, coils and oxygen sensors are listed in the project scope.
Source: Documented work list
Exhaust
Top Gear manifolds and 200-cell catalytic converters; the author later found the configuration too loud above roughly 4,500 rpm.
Source: Documented work list · 5,000-mile follow-up
Reported outcomes
Owner-reported peak power
379 bhp
Published rolling-road figure; no independent verification or graph reproduction is provided here.
Source: Reported rolling-road figures
Owner-reported peak torque
336 lb-ft / 456 Nm
The paired figures are preserved; the thread's "lb/ft" shorthand is normalised to conventional "lb-ft" torque notation.
Source: Reported rolling-road figures
Owner-reported torque at 3,000 rpm
440 Nm
A separate low-speed torque point posted by the author.
Source: Reported torque at 3,000 rpm
Owner follow-up
15,000 miles
At the latest reviewed update the owner reported no oil top-up after the first 1,000 miles and a successful service and MOT.
Source: 15,000-mile follow-up
Evidence limits
- The exact engine code is not stated in the reviewed forum posts.
- Dyno figures, graph and mileage reports are owner or builder statements and were not independently verified.
- The site's summary does not reproduce the forum's dyno image or project photographs.
- The exhaust noise judgement is the owner's experience, not a measured sound-level result.
Access note: The complete thread and cited posts were publicly readable without an account when reviewed.
Reviewed source trail
- Complete 911UK thread · reviewed 2026-08-23
- Opening post · reviewed 2026-08-23
- Cylinder findings · reviewed 2026-08-23
- 4.1-litre decision · reviewed 2026-08-23
- Mid-range response objective · reviewed 2026-08-23
- Documented work list · reviewed 2026-08-23
- Reported rolling-road figures · reviewed 2026-08-23
- Reported torque at 3,000 rpm · reviewed 2026-08-23
- 5,000-mile follow-up · reviewed 2026-08-23
- 15,000-mile follow-up · reviewed 2026-08-23