Originally Posted by SubieRubyRoo
Originally Posted by DoubleWasp
Depends on the engine, mostly the Volumetric Efficiency. How much air and fuel gets into the cylinder per pump of the piston at WOT. Engines that have high VE above 5252 rpm will continue to increase torque past that limit. This is seriously uncommon in street engines, but the Honda S2000 is one exception that I believe does this.
There is always torque. Think of horsepower as the effect of torque causing rpm. Torque can exist with or without rpm, but because there is nothing locking a crankshaft in place, it spins in response to the actions of explosions acting on the Pistons and rods.
So why is the torque dropping after 5252 say on your typical V8? That's because of the design of the engine. The engine is designed for best cylinder filling of air and fuel (through tuning of the intake/exhaust velocity) at lower rpms, for most torque where it will be used the most. The smaller and longer tracts are great at doing at this at lower rpms. The smaller and shorter camshaft durations and lifts are also great at doing this. But there is a limit.
At higher rpms, the engine starts to choke a little. Intake runners are too small to flow the air the cylinder wants, long enough that restriction is increasing, and those valves are too small and aren't open big enough or long enough to meet demand. VE at that speed begins to suffer. Torque past the limit of greatest VE begins to drop. But guess what? The engine is still increasing in rpm. It's doing a bad job of processing air and fuel efficiently, but it's still getting by. It's getting less air and fuel per pump of piston but it's doing a lot more pumping.
Less force of torque, but still more actions are being performed by the torque that is being produced, and hence the horsepower number is still above the torque number.
If you look at those dyno sheets, you will see that horsepower takes a dump not long after torque takes a dump as VE becomes so bad that the engine is literally hitting a wall, or the electronic or mechanical rpm limit just shuts the whole thing down before the engine flings into pieces.
It's been quite some time since I've seen anything as blatantly false as the garbage you spewed here. HP and torque crossing at 5252rpm has nothing whatsoever to do with the design of the engine, and has absolutely everything to do with the way HP is calculated.
The truth about TQ and HP
It's hasn't been a long time since I have dealt with a person who chose to comment without reading.
At no point in either of my two posts do I EVER address the crossing of HP and Torque at 5252rpm. Only which direction torque goes after 5252rpm and why.