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Can someone explain torque vs. engine speed?

calonzo

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as Myx was saying, let's say that at 2500rpm, the rod takes 300ft-lbs or torque over 0.1s(making up numbers here) between when it's at the top of its course to where it's at the bottom and the exhaust valve starts to open(power stroke). The rod material is able to withstand 300 ft-lbs max(let's say).

Now, at 5000 rpm, the rod spends 0.05s in its power stroke, same 300 ft-lbs. It will take twice as much torque to give the rod the same amount of force over the power stroke to make it fail since it stays in that load for half the time.

The same goes for nitrous, if you hit nitrous too early, it creates too much torque due to the increased fuel and air entering the engine and you will grenade your engine because the rods spend too much time in the power stroke and the pressure on them bends and eventually breaks them. If you spend less time in that power stroke, it's less time for the pressure to bend the rod. You very rarely snap a rod clean, it'll almost always bend before it breaks.
Ok, so you are saying that it's not just the force that is exerted that determines if the connecting rod will break, but for how much time the force is being exerted on it.

I guess if we are talking about nearing the max force that the connecting rod can take, then I would agree that the duration under that load is a factor to its failure.

My response to that is that you shouldn't increase the load to the maximum force. If you stay below the maximum force, then no matter whether the force is at a lower or higher rpm, it should be equally safe (up to the max rpm of the engine).
 

Benster

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Ok, so you are saying that it's not just the force that is exerted that determines if the connecting rod will break, but for how much time the force is being exerted on it.

I guess if we are talking about nearing the max force that the connecting rod can take, then I would agree that the duration under that load is a factor to its failure.

My response to that is that you shouldn't increase the load to the maximum force. If you stay below the maximum force, then no matter whether the force is at a lower or higher rpm, it should be equally safe (up to the max rpm of the engine).
Yes, if you stay below what the rod can handle it shouldn't break. Then we get into detonation...that's why we have kcontrol on our computer to limit it, but detonation still happens a little. For those who don't know what happens when an engine detonates is when the power stroke starts pushing down on the piston before it reaches the top dead center. This puts EXTREME pressure on the rods and is the most common reason for engine failures. A bad tune exarcerbates this issue a lot. Detonation will put more pressure than what the engine without knocking would do, which means even with 200ft-lbs, a 300ft-lbs rod could still break under a lot or detonation.

Best way to keep detonation is a safe tune and a lot of octane, don't push the engine as far as you can timing and boost-wise.
 

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