Porsche 911 Modified

Porsche 911 Modified

Coupé, 1971


  • GT3 fast
  • 3.8 litre / 340 hp / 980 kg
  • G50 gearbox

In 1973, Porsche introduced the M491 for racing. The Renn Sport Reunion (RSR) was officially born. Of the 1580 RS’ built, only 55 became the legendary ´73 RSR race car.

This car is a worthy recreation of the famous ’73 RSR and is a true trackday weapon as well as a rewarding drivers car. Road registered in Denmark and formerly road registered in France.

It is stripped down as a true race car – no nonsense and lightened as much as possible – 980 kg with fluids.

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The vehicle in detail

On a track this car is able to keep up with 996 GT3 RS, 997 GT3 RS and 991.1 GT3 – but of course much more fun and demanding to drive.

It was specially built by Belgian classic race driver and builder, Marc De Siebenthal for a French enthusiast..

He built the car by hand on a 1971 road registered stripped down frame and strengthened the weaker parts with welded steel plates to make the car strong and race durable.

The Danish present owner bought it from him in 2014 as a serious replacement for his at that time newly sold 996 GT3 RS. The goal was to get a trackday weapon just as fast but also just as fun as the 996 GT3 RS. And exactly that he got!

The engine is a 3.8 litre 964 engine with Jenvey Throttle bodies

The gearbox is a durable G50 to handle this amount of power – with 996 GT3 limited slip differential and gearbox cooling like a true race car and a raised shifter close to the steering wheel.

In front, the car is fitted with a 100L racing fuel cell from ATL as well as 3 fuel pumps and a scavenge tank. This makes it less likely that the fuel pumps will starve due to fuel slosh when cornering and braking.

The engine is cooled by a front mounted special made oil cooler in the centre of the front.


The vehicle in detail:


3.8L 964 with Mahle machine-in pistons & cylinders

340 HP / 6800 RPM

Jenvey Throttle bodies with carbon housed Jenvey air filters.

Schrick camshafts specifically designed for the 964 RSR and 993 RSR with throttle body kits

Crankcase is modified with dowel pinning

Crankshaft is balanced

Bosch Motronic and dual ignition

Special made Dansk RSR muffler with chambers to make it possible to go 95 dB

Sachs racing clutch with single mass flywheel



Bilstein RSR coilover suspension kit with much more stiffer H&R coils (not the ones on the pictures)

993 turbo front calipers

930 turbo rear calipers

Wheels: 15” Braid ultra-light  9” front and 11” rear mounted with Michelin TB5+ / Toyo Proxes R888



Car is fitted with fibreglass on:

Front bumper

Rear bumper

Hood (carbon/Kevlar)

Doors (fibreglass/carbon)

Rear spoiler/lid

Front fenders

Rear fender extenders

All windows made from Lexan, except front window screen.

Roll cage with strengthened welded mounting points

FIA approved Recaro nomex seats


Sold on behalf of a trusted client / Im Kundenauftrag.


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Year of construction: 1971
Model: 911 Modified
Body: Coupé
Series: 911 Backdate/Modified
Mileage: 100000 km
Power: 340 HP
Cylinder capacity: 3.8 Liter
Steering: left
Transmission: Manual
Drive: Rear drive
Fuel: Gasoline
Interior color: Black
Interior material: Fabric
Exterior color: Silver
Condition: Fully restored
New / used: Used car
Ready to drive: yes
Registered: yes

More information

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Michael Knudsen

Michael Knudsen from autoklasse looks forward to your questions and is happy to help you.

Porsche 911 Modified

Price: EUR 199,900

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