The more I read about this engine the more it seems like this thing is putting out (or has the potential if not for the tq managment) more than is advertised.

Clues:
LS4 specs
5.3L OHV, 2 valves per cylinder
Compression ratio: 10:1
Horsepower (hp / kw @ rpm): 290 / 216 @ 5200 (estimated)
Torque (lb-ft / Nm @ rpm): 325 / 441 @ 4000 (estimated)
Recommended fuel: 92 octane recommended
Maximum engine speed (rpm): 6100

L33 specs (silverado Vortec H.O)
5.3L OHV, 2 valves per cylinder
Compression ratio: 9.5:1
Horsepower (hp / kw @ rpm): 310/231 @ 5200
Torque (lb-ft / Nm @ rpm): 335/452 @ 4000
Recommended fuel: 87 octane
Maximum engine speed (rpm): 5900

LH6 specs (Trailblazer w/ DoD)
5.3L OHV, 2 valves per cylinder
Compression ratio: 9.5:1
Horsepower (hp / kw @ rpm): 300/216.3 @ 5200
Torque (lb-ft / Nm @ rpm): 330/438.7 @ 4000
Recommended fuel: 87 octane
Maximum engine speed (rpm): 5900

Based on these specs you would think the LS4 would be the most powerful, anyone know the specs on the intake and cam? Also note how Pontiac list the HP/TQ as estimated, They did that with the 340HP pre-production GTO too.

 

I think the LS7859003 is (or will be) underrated.

Just thought I'd throw that in, as everything seems to be underrated on the internet these days.

 

1. The old-tech slushbox is "torque limited," to say the least.

2. Transverse placement can lead to less than ideal induction and exhaust systems.

3. I wouldn't read too much into the V8-powered Grand Prix GXP. This car looks and smells like a desperation move.

 

Whether it's underrated or not is hard to say, they could limit its output based on the application.

Having said that, its potential is probably in the 330 - 360 HP range with correct tuning for a factory. We all speculated earlier (perhaps even educationally guessed!) that should LS4 end up as entry level V8, it'll push in the neighbourhood of 350 HP, a safe assumption in my opinion.

It's like Nissan's VQ engine. 260 in current G35 sedan, 287 in 350Z, and 298 in 2005 models. A little tuning and massaging. Besides, the LS4 to be put in our hoped for coupe will be 3 years from now - I think it's safe to assume the numbers will climb up.

 

Sorry guys. I know this one is not false. Altho the engine displacement is the same as the truck engine, so many parts had to changed for the transverse mounting. IN fact, in that configuration, the exhuast routing makes it extremely hard for emisson requirements to be met. Therefore, those restrictions are making anything north of 300 hard. (BTW: the offical rating will be raised to 300 right before production)

 

I guess you worded it better. Stuffed under a cramped FWD hood in a restrictive manner the LS4 might be chokedback to 300HP. But an LS4 engine running with the same air/exhust flow as the L33 & LH6 is going to be putting out more HP than the L33 & LH6 IMO