every single stock GNX that has been on a dyno has gotten nearer 300hp, so chalk up one more for American car manufacturers under-rating their engines to keep insurance prices sane.
That really annoys me too. TVR rate the Chimaera 500 at 320hp (or I think 340, depending on model) but everybody who has had one dyno'ed says they get around 250-270hp, so you have to pay insurance on a car with a 340hp engine, but actually get a car with 270.
TVR marketing
My question is.... would you have to declare any engine mods that pushed the power back up to the manufacturers stated output?* I mean, it would be a bit harsh to go to your insurer "I have just put this mod on, which gives my car an extra 30hp" and the insurer to say "Hey, you must pay more as your car is now classed as 370hp" even though your mod has still only brought the car to 300hp, 40 less that the stated output.
I suppose you could add the mod, dyno it, and then say to your insurer "I've had my engine modified" and when they say "Oh, has that increased HP?" you can truthfully say "well, TVR said it put out 340hp, and after my mod it only puts out 300hp, so my mod has apparently dropped the manufacturer specified power output by 40hp" and get a reduction on your premium
* to whom it may concern, that was a theoretical question, I don't need an answer, obviously all mods should be declared!