Doesnt make any sense to me.

 

Two thoughts (no direct knowledge):

1) Slightly more fuel efficiency with the 400 HP motor so that when combined with the auto, it doesn't get hit with the gas guzzler tax.

2) Slightly lower powerband (ie...better low-mid range power/torque) with the 400 HP motor, improving the "feel" of the car with the automatic.

Both of those goals could be accomplished with the same basic motor, but with a slightly longer intake runner package and different cam profile on the 400 HP motor - though I have no idea what they actually did.

 

They wanted a V8 with active fuel management (AFM), but for some reason AFM will only work with an auto.

Therefore the manual will come with the LS3, and the auto will come with the L99 - basically an LS3 with AFM.

Also, for what ever reason the L99 has slightly less power than the LS3.

 

That makes perfect sense (come to think of it, seems I read that somewhere), and youl almost certainly know a lot more about it than I do.

Bob

 

could it just be a rating and the actually hp numbers are close? GM has underated motors before when in reality they are the same power

 

If GM had the ability to fudge numbers like they used to they would have most likely put them at the same rating. However because of SAE certified ratings, they came up with those different hp numbers for the LS3 and L99.

 

Automatics generally have more drivetrain loss too. I wonder if that had anything to do with the ratings.

 

i think the engines are rated on engine dynos so its measuring actual crank losses and trans effects are not seen there

 

right, they are rated at the engine, not at the wheels.

I betcha it has something to do with AFM limiting the RPM.

 

Regular fuel vs premium would make a difference also. Reminds me of my 96 LT4 Collector Edition Vette where you could only get the 6 speed with the 330hp LT4. So the L99 with AFM is only available with the auto and the LS3 is only available with the stick.

 

ya i dont think the intake is going to be any different. The L76 in the G8 has AFM and its pretty much the same engine other than being a 6.0 vs a 6.2 and it too has the same intake as the LS3. A major difference besides having SLIGHTLY lower compression giving it the ability to use lower octane fuel, though, is that the L76 has vs. the LS3 is GM cut corners and put solid (heavy) valves in the L76, which reduced it's ability to rev (which the afm probably hindered anyways). The L99 im thinkin has the solid valves as well, which could be a factor in changing out the cam and longevity of the springs.

 

What I have been told, not by a GM engineer though, is that with AFM the special lifters limit both revs and valve lift. If that is true then they probably had to limit engine speed and cam profile and found out that they could save a few dollars per motor with solid valves in the L99 and not loose any performance.

Or since this is all speculation anyway, maybe they use the hollow valves anyway but just limit the cam lift and or ramps and the engine speed. Who knows. But it is probably not the case that it is simply engine speed that accounts for the 20 HP since they are rated at the same RPM anyway.

 

Heck during the 3rd gen days Chevy had 2 different power outputs for the auto and the manual with the 5.0 motor.

 

It is all about making sure that the Camaro does not have a Gas Guzzler tax which would kill sales. I am sure if the GG tax was not a factor they would only offer the LS3. My guess is with a computer tune you can get the same performance with the auto and L99 as with the manual LS3

 

maybe. but im sure mod vs. mod the LS3 > L99.