The Stovebolt Site Forums The Shop Area Engine Shop Push rod power!!!

Some one once told me pushrod engines create more torque than non pushrod engines. When I asked why he dint know, can you tell me?

Hy Odd Bolt, basically the longer the stroke the more torque an engine will produce, there are lots of other factors as well, but how the valves are actuated, by a pushrod/rocker arm setup, or overhead camshaft, doesn't contribute much to torque production, overhead camshaft engines generally have less internal friction, so more useable power is produced.

What 3B said. Valve actuation has absolutely nothing to do with the amount of power an engine is capable of. The bore/stroke ratio and dimensions, valve timing, valve size, combustion chamber geometry, volumetric efficiency, fuel quality, fuel/spark map and state of tune are what determines the amount of torque and engine produces

Back in the 50's some people referred to a overhead valve engine as a push rod engine. And of course the valve in head engines were more powerful than their L head predecessors.

It's also not so much that pushrod engines make "more" torque, but that pushrod engines tend to make it at a much lower rpm band. As Scott pointed out, that comes more from the operating parameters, but there's also the consideration that in addition to being tuned to a higher rpm range, OHC engines also breathe much better, namely due to having more valves per cylinder. Which brings us to the L head and Overhead comaprison. Overhead valve engines breathe better than L head engines. The you have the F head, which is a comprimise.

OHC engines also breathe much better, namely due to having more valves per cylinder

...when they do.

more valves does not indicate better breathing. Combustion chamber and valve geometry determines that, whether it is 2 valves, or 5 valves per cylinder. intake tract geometry, valve shrouding, intake harmonics, engine exhaust scavenging etc. all determine engine breathing. If you want an engine to really breath, force feed the intake and suck out the exhaust.

Let me rephrase myself. OHC engines tend to have a more favorable valve layout, generally with a hemispherical combustion chamber. Intakes on one side, exhausts on the other. It has also been proven that multiple smaller valves will flow better that one large valve, another trait common to the OHC head layout. This also runs hand in hand with everything Scott said.