What I don't get is why the 6.9 has a problem with piston speed (apparently), but other engines of a similar size (or bigger) don't and seem happy to rev higher??
M100, 6.9
Bore and stroke = 107mm x 95mm
Displacement = 6,834 cc
Compression Ratio = 8.8:1
Max HP = 286 bhp @ 4250 rpm
Max Torque = 405 lb/ft @ 3,000 rpm
455 Buick
455.72-cubic-inch (7,467.9 cc)
4.31 in (109 mm) bore and 3.90 in (99 mm) stroke
Std 350 hp (260 kW)
Stage 1 360 hp (270 kW).
Std 510 lb·ft (690 N·m) of torque at 2800 rpm (more than any other muscle car engine).
The 455 was one of the first "thin-wall casting" engine blocks (at GM), and because of this advance in production technology it weighs significantly less than other engines of comparable size (for example, 150 lb (68 kg) less than a Chevrolet 454 and only 25 lb (11 kg) more than a Chevrolet 350).
From what I understand the LS engines have tiny (short skirt) pistons which could account for the difference...
LS7
7,008 cc (7.008 L; 427.7 cu in)
4.125in (104.775mm) bore and 4.00in (101.6mm) stroke
505 hp (377 kW) at 6300 rpm
470 lb·ft (640 N·m) at 4800 rpm with a 7100 rpm redline
The crankshaft and main bearing caps are forged steel
The connecting rods are forged titanium
The pistons are hypereutectic
Titanium intake valves 2.20 in (56 mm)
Sodium-filled exhaust valves 1.61 in (41 mm).
During GM's reliability testing of this engine in its prototype phase, the LS7 was remarked to have been repeatedly tested to be 8000 rpm capable, although power was not recorded at that rpm level, due to the constraints of the camshaft's hydraulic lifters and the intake manifold ability to flow required air at that engine speed.
Holden Special Vehicles fitted the LS7 to a special edition model, the W427. The HSV-tuned engine produced 375 kW (503 hp) and 640 N·m (470 lb·ft), at the time making it the most powerful car ever built in Australia.
