Isdera Imperator 108i

Which Isdera Imperator 108i version to choose

The Isdera Imperator 108i is a Coupe with 1 generation, built from 1984 to 1993, and the buying question is which of the 4 versions to take. All four share the same production window, the same Coupe body, rear-wheel drive labelled RWD, a 5-speed Manual, no forced induction (No), a 106-litre tank, and 135 mm ground clearance.

Which Isdera Imperator 108i version to choose

The Isdera Imperator 108i is a Coupe with 1 generation, built from 1984 to 1993, and the buying question is which of the 4 versions to take. All four share the same production window, the same Coupe body, rear-wheel drive labelled RWD, a 5-speed Manual, no forced induction (No), a 106-litre tank, and 135 mm ground clearance. The spread that actually decides the car is engine size, cylinder count, output, and whether kerb weight is measured: 5.0 MT at 231 hp, two different 5.5 MT cars at 300 hp and 388 hp, and 6.0 MT at 408 hp.

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Isdera Imperator 108i generations (1984–1993)

There is only one generation, so there is no later generation that changed body type, drive, gearbox count, or tank size. The generation runs 1984-01-01 to 1993-12-31, body Coupe, 4 versions. Searches for “series 1”, “series 2”, “mk2”, or a 1991-only car do not map onto a second generation in this data: every version is listed with the same start and stop dates. Choosing a year inside 1984–1993 does not, on these figures, unlock a restyle generation. The choice is between the four powertrains inside that one Coupe.

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Isdera Imperator 108i specs: engines compared

Use the table as the shortlist. Two rows are both named 5.5 MT; they are not the same car — separate them by 300 hp versus 388 hp.

What the extra displacement buys

• 5.5 MT (both) versus 5.0 MT: +488 cc (5461 − 4973). That extra half-litre stays on 8 cylinders, V-shaped, No boost, Manual 5, RWD.
• 6.0 MT versus either 5.5 MT: +526 cc (5987 − 5461) and a jump from 8 to 12 cylinders, still V-shaped, still No boost.

Power per litre (hp ÷ displacement in litres)

• 5.0 MT: 231 / 4.973 ≈ 46.5 hp per litre — the lowest specific output of the four.
• 5.5 MT (300 hp): 300 / 5.461 ≈ 54.9 hp per litre.
• 5.5 MT (388 hp): 388 / 5.461 ≈ 71.0 hp per litre — the highest specific output.
• 6.0 MT: 408 / 5.987 ≈ 68.1 hp per litre, slightly below the 388 hp 5.5 MT despite more total horsepower.

If the goal is the most work from each litre, the 5.5 MT at 388 hp wins the arithmetic. If the goal is the largest engine and the highest peak horsepower, 6.0 MT at 408 hp is the top of the list by 20 hp (408 − 388) over the stronger 5.5 MT, a ≈5.2% step.

Valves, injection, and engine position (only where measured)

• 5.0 MT: valves per cylinder not measured; engine position not measured; fuel system not measured; compression not measured; bore × stroke not measured.
• 5.5 MT (300 hp): 3 valves per cylinder, engine position Central, fuel system Distributed injection (multi-point), compression 10.7, bore × stroke 98 × 90.5.
• 5.5 MT (388 hp): 4 valves per cylinder on the same 5461 cc, 98 × 90.5, 10.7, Central, Distributed injection (multi-point). Same swept volume as the 300 hp car; the listed difference is +1 valve per cylinder, +88 hp (388 − 300), +30 Nm (530 − 500), peak power 1000 rpm higher (6000 versus 5000), and fuel grade 98 instead of 95.
• 6.0 MT: 4 valves per cylinder, 12 cylinders, Central, Distributed injection (multi-point), compression 10 ( 0.7 lower than both 5.5 MT cars), bore × stroke 89 × 80.2.

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Isdera Imperator 108i top speed, 0–100, and mpg

City, highway, and combined consumption are not measured on every version, so none of the four can be ranked on mpg from this data. CO2 and eco class are not measured on all four.

0–100 km/h

• 5.5 MT (300 hp): 5 s — the only version with a measured sprint.
• 5.0 MT: not measured.
• 5.5 MT (388 hp): not measured.
• 6.0 MT: not measured.

Do not treat the missing 5 s figures as “slower than 5 s” or “faster than 5 s”. They are not measured.

Top speed

• 5.5 MT (300 hp): 283 km/h — the only measured top speed.
• 5.0 MT, 5.5 MT (388 hp), 6.0 MT: not measured.

The 388 hp 5.5 MT and the 408 hp 6.0 MT make more peak power than the 300 hp car (+88 hp and +108 hp), but this dataset does not attach a higher top speed or a shorter 0–100 time to them. If a measured sprint and a measured top speed are required to choose, only 5.5 MT at 300 hp supplies both.

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Isdera Imperator 108i dimensions, weight, and tank

Wheel sizes are not measured on all four versions. Ground clearance is 135 mm on all four. Tank is 106 litres on all four. Front and rear suspension are Independent, spring on all four. Front brakes are Ventilated disc on all four; rear brakes are labelled Disc ventilated on all four. Those chassis figures do not separate the versions.

Kerb / gross weight

• 5.0 MT: kerb 1350 kg, gross 1640 kg (payload window 1640 − 1350 = 290 kg).
• 5.5 MT (300 hp): the same 1350 / 1640 kg.
• 5.5 MT (388 hp): kerb not measured, gross not measured.
• 6.0 MT: kerb not measured, gross not measured.

Weight per horsepower where kerb is measured

• 5.0 MT: 1350 / 231 ≈ 5.84 kg per hp.
• 5.5 MT (300 hp): 1350 / 300 = 4.50 kg per hp — ≈1.34 kg per hp lighter than 5.0 MT at the same kerb weight, because output is 69 hp higher (300 − 231, ≈+30%).

For 5.5 MT (388 hp) and 6.0 MT, kg-per-hp cannot be calculated: kerb weight is not measured. Do not assume they stay at 1350 kg.

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Which Imperator 108i version to choose

There is no generation-to-generation swap: one Coupe generation, four engines. The practical split is 8-cylinder versus 12-cylinder, and inside the 8-cylinder cars, three distinct outputs.

Choose 5.0 MT if the brief is the smallest engine and the lowest listed output. 5.0 MT is 231 hp / 170 kW from 4973 cc, 8 cylinders, V-shaped, No boost, fuel 92, Manual 5, RWD. Torque, 0–100, and top speed are not measured. It is the only version on 92. Versus 5.5 MT (300 hp) it gives up 69 hp and 488 cc at the same 1350 kg kerb, so it is the heaviest-feeling power-to-weight pairing that can actually be calculated (≈5.84 vs 4.50 kg/hp). Versus 6.0 MT it gives up 177 hp (408 − 231) and 4 cylinders.

Choose 5.5 MT (300 hp) if the brief is a measured 0–100 and a measured top speed. This 5.5 MT is 300 hp / 221 kW at 5000 rpm, 500 Nm, 5461 cc, 3 valves per cylinder, Central, Distributed injection (multi-point), compression 10.7, 98 × 90.5, fuel 95, 0–100 5 s, top speed 283 km/h, kerb 1350 kg. It is the only row where performance is not a blank. Specific output (≈54.9 hp/L) sits between 5.0 MT and the 388 hp 5.5 MT. It does not have the peak power of the other 5.5 MT (88 hp less) or of 6.0 MT (108 hp less), and torque is 30 Nm below the 388 hp car and 80 Nm below 6.0 MT (580 − 500).

Choose 5.5 MT (388 hp) if the brief is the strongest 8-cylinder and the highest specific output. This 5.5 MT keeps 5461 cc, 8 cylinders, V-shaped, Central, Distributed injection (multi-point), 10.7, and 98 × 90.5, but lists 4 valves per cylinder, 388 hp / 285 kW at 6000 rpm, 530 Nm from 2800–4800 rpm, and fuel 98 — the only version on 98. Specific output ≈71.0 hp/L beats 6.0 MT’s ≈68.1 hp/L. The cost in the data is missing mass and missing performance: kerb, gross, 0–100, and top speed are not measured. Compared with the other 5.5 MT, the extra 88 hp is ≈+29% on the same displacement; compared with 6.0 MT, it is 20 hp short of the catalogue peak but uses 526 cc less and 4 fewer cylinders.

Choose 6.0 MT if the brief is peak horsepower, peak torque, and 12 cylinders. 6.0 MT is 408 hp / 300 kW at 5200 rpm, 580 Nm at 3800 rpm, 5987 cc, 12 cylinders, V-shaped, 4 valves per cylinder, Central, Distributed injection (multi-point), compression 10, 89 × 80.2, fuel 95, Manual 5, RWD. It is the only 12-cylinder Imperator 108i in this set. Versus the 388 hp 5.5 MT the gains are +20 hp, +50 Nm, +526 cc; versus 5.5 MT (300 hp) they are +108 hp and +80 Nm. Kerb weight, 0–100, and top speed are not measured, so it cannot be shown as quicker than the 300 hp 5.5 MT’s 5 s / 283 km/h on this page.

Short ranking by the numbers that exist

• Highest hp / kW: 6.0 MT (408 / 300).
• Highest Nm: 6.0 MT (580).
• Highest hp per litre: 5.5 MT (388 hp).
• Best calculated kg/hp: 5.5 MT (300 hp) at 4.50 kg/hp (5.0 MT is 5.84; the other two lack kerb).
• Only measured 0–100 and top speed: 5.5 MT (300 hp) — 5 s and 283 km/h.
• Only 12-cylinder: 6.0 MT.
• Only 92 fuel: 5.0 MT. Only 98 fuel: 5.5 MT (388 hp). The two remaining versions use 95.
• Same tank, clearance, drive, gearbox type and count, boost, body, and years on all four: 106 L, 135 mm, RWD, Manual 5, No, Coupe, 1984–1993.

Price and cars for sale are not in this dataset, so “extra money” here means extra displacement, extra cylinders, extra hp, and extra Nm — not a sticker. If the buyer needs figures that are actually filled in (weight plus sprint plus top speed), the version that has them together is 5.5 MT at 300 hp. If the buyer wants the strongest 8-cylinder on paper, it is 5.5 MT at 388 hp. If the buyer wants the catalogue maximum of power, torque, and cylinder count, it is 6.0 MT. 5.0 MT is the entry by output and by litres, with more blanks on torque and performance than the 300 hp 5.5 MT.