[HIGHOCTANE]

Originally Posted by joelster

I just read through this whole thread and none of you guys answered the Op's question as to why the Ford motor is more efficient, lol.

It has A LOT to do with 4-valves per cylinder for the Ford vs 2-valves per cylinder for the Chevy. In a round cylinder which all motors have, if you are running 2 valves (1 intake and 1 exhaust) and they aren't canted much you can only go to roughly 2.1" on the intake and 1.7" on the exhaust with a 4" bore. On the Ford design you can run 2- 1.5" intake valves and 2- 1.2" exhaust valves, with a 4" bore. The actual surface area of the Ford intake and exhaust valves is substantially higher vs the Chevy valves.

What does this mean?

In a nutshell, it means at any given valve lift, the Ford has the ability to pack more air and fuel into the cylinder if the cylinder were the same size as the Chevy. In this particular case Ford went with a smaller cylinder and smaller displacement (5.0), but it is actually cramming about the same amount of air/fuel into it as the Chevy (6.2)motor.

There are other factors at play here such as the intake manifold efficiency, the intake runner design which doesn't have to concern intself with pushrods getting in the way, and friction losses due to pushrods and rocker arms, but the big difference is the number of valves per cylinder.

IMO the Chevy Engineers have worked hard to keep the push rod motors in the game...and have done an excellent job.
The 4V motors breathe very well...simple physics...they have an advantage....a 6.2 DOHC 4V engine designed by the GM engineers would be SICK...I reaslly hope they go this route with the Z....it doesn't need a blower or more displacement...4V DOHC JMO