Rünge Cars’ Hetzer is a bespoke, naturally aspirated, air-cooled 5.3-liter flat-eight designed around the packaging dimensions of the Porsche 964’s M64 flat-six. Road & Track reports a 9,000-rpm redline and a 10,000-rpm electronic limiter; roughly 600 horsepower is an expectation, not a published dyno result. Its reported dimensions make a 964 installation a design goal, not proof of a universal drop-in fit.
What is the Rünge Hetzer?
The Hetzer is an air-cooled, naturally aspirated flat-eight developed in connection with Rünge Cars’ R3 project. Road & Track’s July 2026 reporting gives its displacement as 5.3 liters and describes four camshafts, 32 valves, a 9,000-rpm redline and a 10,000-rpm electronic limiter. Those are reported design specifications, not results from an independent test.
The concept draws on a familiar Porsche layout but adds two cylinders to the flat-six arrangement. In a flat engine, cylinders lie horizontally on opposite sides of the crankshaft. Porsche says that configuration can keep an engine low in the chassis; in a rear-engine car, the engine’s weight also sits over the driven axle. Those are general characteristics of the layout, not evidence of a particular handling gain from the Hetzer.
Will it fit in a Porsche 964?
It was designed with the 964’s M64 engine packaging in mind. Road & Track reports that the Hetzer was packaged within 2 mm of the M64 flat-six dimensions, while Car and Driver’s October 2025 report says it was built to fit a 964 engine bay. That close dimensional target is notable for an eight-cylinder engine, but it does not establish that every 964 can accept one without changes.
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- Die-cast metal body with plastic parts
- Opening doors and engine compartment
- Detailed chassis
- Package Dimensions: 10.6 L x 23.5 H x 11.5 W (centimeters)
The reporting does not specify installation labor, the modifications a particular car may need, or road legality. Packaging dimensions alone do not answer questions about a specific chassis, ancillary systems, or local compliance. Rünge Cars is the appropriate source for current, vehicle-specific installation information.
How much power does the Hetzer make?
About 600 horsepower is the reported expectation, not a confirmed output. Car and Driver explicitly noted in October 2025 that dyno results had not been released; the newer Road & Track account also presents the figure as expected rather than as a measured result. The reviewed reporting provides no like-for-like dynamometer comparison with the Porsche M64 flat-six.
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That distinction matters: a redline and a cylinder count describe the design, while verified horsepower requires published measurement conditions and results. The available sources do not provide those for the Hetzer.
How it compares with the 964’s M64 flat-six
| Feature | Rünge Hetzer | Porsche 964 M64 |
|---|---|---|
| Configuration | Air-cooled flat-eight; four camshafts and 32 valves, as reported by Road & Track. | Flat-six baseline; the reviewed Hetzer reporting does not provide a full M64 specification comparison. |
| Displacement | 5.3 liters, reported by Road & Track. | Not stated in the reviewed Hetzer reporting. |
| Power | Approximately 600 hp expected; no published dyno result in the reviewed reporting. | No like-for-like output figure established by the reviewed sources. |
| Packaging | Reported within 2 mm of the M64 flat-six dimensions by Road & Track. | Reference packaging envelope for the design comparison. |
The comparison is therefore strongest on architecture and packaging: the Hetzer adds two cylinders while targeting dimensions close to the M64 envelope. It is not a verified power contest or proof of interchangeability.
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Why an air-cooled flat-eight is an unusual proposition
Porsche’s explanation of flat engines helps clarify the engineering tradeoff. Opposed cylinders create a low-profile layout, but a flat engine has two cylinder banks and their associated valvetrain, cooling and injection arrangements. Porsche notes that this complexity generally makes flat engines more demanding to manufacture than inline engines. The Hetzer’s reported eight-cylinder, 32-valve specification makes it a particularly elaborate expression of that format; the available accounts do not establish its durability or service requirements.
What is known about its development and availability?
Road & Track identifies Rünge Cars as the owner of the Hetzer design and distribution, and describes Swindon Powertrain in the engine’s development history. That history does not establish Swindon’s role in current sales or support. Rünge’s Runge RS page shows the company’s other low-volume, hand-built Porsche-inspired work, but it is not a Hetzer listing.
The reviewed sources do not settle a current price, order availability, delivery timing, emissions certification or measured output. Readers considering a project should seek current details directly from Rünge Cars rather than treating the reported packaging target or projected power as an offer or guarantee.
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