Documented owner build record · 993 · air-cooled
993 3.6 to 3.8 conversion, Tech 9
A burnt exhaust valve turned into a full 3.8-litre conversion: 102 mm Mahle pistons and cylinders, a machined case and rally-profile cams, published by the owner with a costed decision trail and a reported 320 bhp and 292 lb-ft.
Evidence: Complete build write-up
- Vehicle
- Porsche 993 Carrera S
- Engine
- 3.6-litre 993 flat six with leaks at the chain housings, power steering pump housing, cam covers and through bolts, and 80% leakage past the cylinder 5 exhaust valve → 3.8-litre flat six on 102 mm Mahle pistons and cylinders in a machined case, with Tech 9 rally-profile cams, vernier cam drive wheels and uprated head studs
- Published at
- Air Cooled Bug
- Author
- Mr Coyne · 14 April 2019
Vehicle and engine evidence: Complete build write-up · The car's index page on the same site
Why it came apart
Oil leaks worse than the pre-purchase inspection suggested, consumption close to the handbook tolerance limit, and a leak-down test returning 80% leakage through the cylinder 5 exhaust valve — found to be badly burnt once the engine was opened.
Source: Complete build write-up
What the project aimed to do
A quicker 993 with noticeably more go: a car able to cross Europe at pace, keep up with modern traffic on an autobahn and still behave in London traffic. The author explicitly asked Tech 9 to aim at torque and driveability rather than a headline power figure.
Source: Complete build write-up
Who did what
Tech 9 Motorsport in Hale specified and built the engine to the owner's brief; the owner chose the builder after comparing Tech 9 with Nine Excellence and visiting both. Tech 9 reported progress weekly by email with photographs uploaded to a Flickr gallery, and delivered the build in seven weeks against a six-to-eight-week estimate.
Source: Complete build write-up
A Varioram wide-body 993 that the author compares directly with a standard 993S, later driven across the United States. The page does not state the model year, and gives mileage only in passing while arguing that a top-end rebuild at 150,000 miles would be a half job.
Vehicle context: Complete build write-up · The car's index page on the same site
Documented sequence
Diagnosis and the decision to go further
The leak-down result made the cylinder 5 exhaust valve the immediate problem. The author sets out why they rejected a re-seal and a top-end rebuild: a re-seal would not last, and a top end at that mileage would leave the known leaks at the chain housings, power steering pump housing and through bolts untouched. Splitting the case for a full rebuild puts the pistons and cylinders on the bench anyway, which is where the 3.8 option arises.
Source: Complete build write-up
Choosing a builder and costing the options
The page publishes the builder shortlist and a median cost band for each level of work — re-seal, top end, full rebuild and 3.8 — while noting that the true extent of the job cannot be pinned down until the engine is out and open, and that Mahle pistons and cylinders alone were around £5,000.
Source: Complete build write-up
Machining and specification change
The case was machined to accept the 102 mm pistons and cylinders. Part way through, Tech 9 proposed adding their rally-profile cams as the best route to the stated brief; one of the existing cams was showing signs of pitting, so that area was going to cost money regardless.
Source: Complete build write-up
Build and weekly reporting
Everything was replaced or renewed around the upgrade parts. The author describes weekly email updates with supporting photographs, and completion in seven weeks — with parts shipped from the USA, sub-contracted case machining and customs all named as timing factors.
Source: Complete build write-up
Collection and road assessment
The car was collected from Liverpool and assessed the same day on the B4391 and A4212 in North Wales, then over a laden run to Cornwall on the A303 and A30, then on a familiar dual-carriageway route in London with the car empty. The author reports each of these separately rather than as a single verdict.
Source: Complete build write-up
Named components and work
Displacement
Mahle 3.8 pistons and cylinders — the author notes these are the same parts Porsche used — with the case machined to accept the 102 mm bore.
Source: Complete build write-up
Camshafts and cam timing
Tech 9 rally-profile cams, with the original slotted cam chain drive wheels replaced by vernier-style wheels so cam timing could be set accurately and, in the author's words, matched very accurately across both banks.
Source: Complete build write-up
Valve train
Lightweight titanium valve retainers and steel valve springs matched to the cam profile for valve control, on uprated cylinder head studs.
Source: Complete build write-up
Rebuild content
The heads were restored and parts vapour blasted; cam covers, belts, filters, O-rings, bearings, seals, gaskets, studs, chains and valves were all replaced or renewed.
Source: Complete build write-up
Reported outcomes
Owner-reported power and torque
320 bhp and 292 lb-ft (395 Nm)
Published as the build's numbers, at 217 bhp per tonne with hollow-spoke wheels fitted and the lightweight flywheel not deducted. The author sets them against a standard 993S at 281 bhp and a 993 RS at 296 bhp, and immediately points out the RS is 205 kg lighter. No dyno graph is reproduced on the page.
Source: Complete build write-up
Driveability with high-lift cams
No lumpy idle, but a specific cold-start procedure
The author had been apprehensive that aggressive cams would make the car irritating in traffic. They report it behaves close to standard once warm, provided the key is turned without touching the pedals and the engine is left to settle for about a minute; touch the throttle during that period and it stalls repeatedly.
Source: Complete build write-up
Where the change is felt
Torque in third and fourth, and cams coming alive around 4,000 rpm
The author attributes the stronger mid-range directly to the larger pistons and cylinders, and describes the rally cams as almost turbo-like from around 4,000 rpm where the Varioram comes in.
Source: Complete build write-up
Fuel consumption
Roughly one to two mpg worse on a long run
Best post-build figure around 28-29 mpg against 30-31 mpg before; the author reports no change in their usual 24-25 mpg driving, or around town.
Source: Complete build write-up
Evidence limits
- The power and torque figures are published as a result without a dyno sheet, run conditions or correction factor on the page.
- The author states plainly that they have no pre-build acceleration or top-speed data, so no before-and-after timing comparison exists.
- The side-by-side run against a 997S is described by the author himself as hardly a scientific test.
- The invoice reproduced at the foot of the page is acknowledged to be incomplete — the vernier pulleys went into the engine but not onto it, and some diagnostic work was billed separately.
- The model year and the mileage at rebuild are not stated directly; the page refers to 150,000 miles only while arguing against a top-end-only job.
- This is a single owner-published account of a professional build, not an assembly procedure, and nothing on the page was independently verified.
Access note: The build page and the car's index page were publicly readable without an account or paywall when reviewed.
Reviewed source trail
- Complete build write-up · reviewed 2026-08-26
- The car's index page on the same site · reviewed 2026-08-26