I was thinking about the difference in power levels between the two following examples:

5.3L Truck A4
5.7L Fbody A4

Mods

5.3L w/ full bolt ons, 220 cam
5.7L w/ full bolt ons, 220 cam

5.3L = 320rwhp
5.7L = 380rwhp

Please do not knit-pick. This is for discussion purposes only. Okay, so why does the 5.3L make 60 less power to the wheels? Please list what you see as a loss and if it's a bit wacko, give an estimated power loss... at least an assumption.

I'll start off:
*Bore size
*Compression

What else?

 

Head flow, intake, and what you said.

 

Friction maybe, aluminum block versus iron?

 

Smaller bore,smaller intake valves,less valve timing and lower compression ratio on the 5.3.Plus the larger displacement 5.7 responds better to the 220 duration cam and the F-body has a better selection of exhaust systems.

 

You also have to think of the drivetrain loses in the trucks compaired to the f-body. Trucks have longer drive shafts, larger rearend and normally larger tires.

 

i think that the aluminum block has iron sleeves though.

 

Its a combination of everything, LS1-(5.7) Larger displacement, better flowing heads, higher compression, Less drivetrain loss in a Fbody( Especially if its a manual) Like previously mentioned with that cam, the LS1 will respond better becuase of larger displacement and better flowing heads.

 

Okay... more friction???
Never heard that one before.

I have head flow figures right here and they show the truck heads keeping up with the LS1 heads (to an extent). Yeah, a few cfm here and there, mainly on the exhaust.
Whitt is correct tho, they do have a larger intake valve so, this may show some difference.
But realistically, how much power is gained by professionally ported heads where an increase of 60cfm @ .6'' is seen? 20-30rwhp? So, the heads can't be a huge contributor.

*Drivetrain loss
*Compression
*Bore size

I think were missing some hp. Compression is only a half of a point. Heads are only marginally better.

I think the intake manifold is contributing to this difference but, everyone seems to think the LS6 doesn't flow better.


Hmmm, definetly can't see that for ****.
It says 5.3L heads 226cfm @ .6'' and 5.7L heads 227cfm @ .6''. Yes, there is more to flow than cfm readings... I'm just posting figures.

 

when you say there is more to flow than cfm readings
are you referring to
velocity and atomization with the different heads?

and even though they flow close to the same numbers,
this doesnt tell you much about how the air fuel mixture will act once it gets past the valve and into the chamber?

 

GD,
No, not really. If you know in what ways the a/f mixture differs please post how. Or, how atomization differences between a 5.3/5.7 head. I'd like to hear it.
Velocity is important but, stock vs. stock.... both utilize a 200/70cc runner combo.
The key difference in flow is going to be that intake valve in my opinion and the larger bore the 5.7 head is allowed to flow into.
To relate this to the topic at hand, I do not believe the LS1 heads make up a large portion of that difference in power. But if you feel they do, please explain how.
Thanks.