Originally posted by lafear01
Pushrods have nothing to do with it! (in case that's what you meant.)
5.0L have better TQ due to 4" bore and shorter 3" stroke! that's the only reason. The DOHC would have great TQ down low if they didn't kill our displacement. FYI :
4.6L = 3.55" bore x 3.54" stroke. IMHO i'd take the 4x3 anyday! just give me the DOHC as well. Then we have a truly great motor!
You're right about the pushrods. A DOHC engine is more reliable, more power efficient, and can operate at higher RPM. But DOHC doesn't itself reduce the available torque.
But you got the stroke / bore exactly backwards. For a given displacement, short stroke / big bore is for high RPM power; and long stroke / small bore is for low end torque.
The longer stroke gives the piston a longer moment arm to spin the crankshaft -- more crankshaft torque. But it makes the piston travel further with each revolution -- limiting high RPM operation, which limits the gearing you can use.
High RPM engines must have a short stroke, in order to reduce the speed of the pistons. They don't necessarily have less torque, but they get their torque at high RPM -- which is A GOOD THING because it lets you use more gearing.
Consider a typical 4-cylinder motorcycle engine -- redline 13,000 RPM, stroke 44 mm, bore 77 mm. High power, low torque.
Now consider a Harley Davidson engine -- redline 5,500 RPM, stroke 107mm, bore 92mm. Low power, high torque.
Of course, the high power low torque engine literally blows away the high torque low power engine in every performance category.