Is the LT4 underrated from GM?
 

I'm just curious if people have found the 650 crank HP rating from GM to be accurate or is it a little underrated like the hellcat? I know this is kind of a silly question and all dyno's are different. 549 WHP would be about 650 crank yeah? Are people seeing higher numbers than that stock?

Not really. Most baseline whp dynos come right in where you'd expect for 650 crank.

But like all things there is a distribution curve so some cars will be a little hot and others a little not.

I feel it’s right where advertised and stays there after several demo runs. Which is what I want. No hero 1 roll run hit wonders like that 2013 A6 LSA ZL1...

I think they are pretty on target. Most are dynoing (not a real word) around 540-550 and depending on the dyno as low as 510. So I’d say pretty accurate.

It's an SAE certified engine so among other things random engines were pulled off the line and evaluated. If they weren't within specified SAE parameters GM would not be allowed to use the rating. If yours is making more or less than advertised you have an issue.

Not underrated, but they sure left a lot on the table if you don't mind throwing your warranty away.

The German cars are typically under-rated, as the advertised numbers are actually the numbers at the wheels, not the crank. They aren't claiming SAE certified though. This allows them to be "compared" with cars that make less HP and torque in auto tests, and of course, in those tests they smash those other cars, making the BMW or Audi or whatever look like golden-children, except if you are going just on HP/TQ, it wasn't a fair fight to start with. The new G20-based BMW 340 is going to put out 382hp and 369ft/lb. Think about that for a second. While not quite as much as an LT1 and it's going to probably end up a bit heavier, that's still a ton of power and the thing is going to GO, a 4-door sedan. Probably sitting at more like 425hp and 415tq at the crank. This why some of the big heavy hitters go so damn fast, in addition to their DCTs and flat torque ranges...they simply have more HP.

That is not his question.:rolling5thgen:

My point was that SAE certified engines will be putting out what they are SAE certified to do, other engines have been "underrated" because the advertised numbers are elsewhere in the system, which may lead to the false perception that other manufacturers do the same thing. As for your perception, don't really care.

Oh. If you didn’t care why did you answer? Its cool. You are blocked. I really don’t care about your pereception.

?

Purely based on numbers.

85% x 650 = 552.5 at the wheels.

85% drive train loss is a general guess but it seems to be about right.
it might be interesting to look at numbers for M6 vs A10 to see if theres much of a difference. Guessing not much if any, the A10 is very modern.

I think this is a good point for someone that may be transitioning from foreign to domestic.

Generally I find that most domestic cars are underrated and I think it's because their quote needs to be considerate of all climates where the car is sold.

So am I wrong if I thought stock hellcats put down 620-630 WHP stock if not a little more?