Bgs88@Personally, I think 250 hp at the wheels is a bit optimistic for a naturally aspirated 2.7 MFI engine. My expectation would be somewhere in the 210–220 whp range if it's a really well-built motor with good heads, cams, compression, exhaust, and proper MFI tuning.
As for the RS crankshaft, I agree it's a very strong component, but I think the magnesium case becomes the limiting factor rather than the crank itself. For that reason, I probably wouldn't rev it much beyond 7,300 rpm if the goal is long-term reliability. An engine built purely for racing and rebuilt regularly is a different story, but for a car that's driven and enjoyed, I'd rather stay on the conservative side.
The final output will, of course, depend on the complete specification. I'd be interested to know more about the build—compression ratio, cam profile, cylinder head work, valve sizes, pistons and cylinders, exhaust system, and how the MFI pump has been calibrated. The L120/104 cams are quite aggressive camshafts and are well known in the air-cooled Porsche world.
They generally have these characteristics:
Strong top-end power.
Weaker torque below about 3,500–4,000 rpm.
Come alive between 4,500 and 7,500 rpm.
Work best with high compression (10.5:1 or higher), twin ignition, good cylinder head flow, and a properly calibrated MFI or EFI system.
So if his engine has:
L120/104 cams,
twin plugs,
10.5:1 compression,
well-ported heads,
and a good exhaust,
then it's a very serious naturally aspirated 2.7.
That said, I'd still be a little skeptical of 250 hp at the wheels. That's roughly 290–300 hp at the crank, assuming about a 15% drivetrain loss, which is extremely ambitious for a 2.7-liter MFI engine. It would be exceptional rather than typical.
A realistic expectation for an excellent engine of that specification would probably be:
260–280 hp at the crank
220–235 hp at the wheels
Those are still outstanding numbers for a 2.7, and very rare figures, started to build engine in 1982
As for revs, the RS crankshaft itself isn't the issue—it's a very robust forged crank. The limiting factors are usually the magnesium crankcase, connecting rods, valve-train stability, and overall engine build quality. That's why I'd still be inclined to set the rev limiter around 7,300–7,500 rpm for a long-lived street/track engine, even if it is mechanically capable of more.
This looks like a fantastic build: an RSR-style 1974 Porsche 911 Coupe with a 5-speed gearbox.
The current engine setup is likely capable of around 210–230 hp at the crankshaft. The magnesium case can become the weak point over time, especially if the car is used regularly on track, but it’s also not a bad thing — building another engine down the road is part of the journey with these cars.
If upgrading in the future, I would personally look at something like a short-stroke 3.2L MFI twin-plug or a 3.4L based on a Carrera 3.2 engine with MFI and twin-plug ignition. In my opinion, these setups offer some of the best horsepower-per-dollar combinations while keeping the character that makes these engines so special.
That said, the car is already fantastic as it sits. Once the major work is completed, adding personal touches such as period-correct seats and a few other details would make it even more special.
This is the type of Porsche that should continue to appreciate over time. The combination of this iconic color, the quality of the build, excellent panel gaps, a well-sorted setup, and the classic 15-inch Fuchs-style wheels is exactly the recipe that works.
My personal favorite engine choice would be the 3.4L twin-plug MFI. It offers a great balance of cost, reliability, and incredible torque. Combined with a race-inspired gearbox setup — a longer first gear, shorter 2nd–4th gears, and a slightly longer 5th for relaxed cruising — it becomes an engine and transmission combination that works beautifully both on the street and on track.
Congratulations on a beautiful build. This is one of the most iconic Porsche colors and one of the best interpretations of a classic 911.
