saving Stock rods by keeping peak torque low ?
12-06-2018, 07:27 PM
#41
In my humble opinion time is a factor up to a point. In a narrower period of time you have elastic deflection that rebounds. During a longer period of time you are more likely to bend something beyond its elasticity and introduce a perminate bend.
The million dollar question is how closely the two are to one another. In all likelihood the delta is so minor as to make the entire concept irrelevant.
Last edited by k24madness; 12-06-2018 at 09:04 PM.
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12-06-2018, 08:13 PM
#44
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The best clause I have seen in this is from Savington... "if you want to".. in this statement: "Keep the timing soft and you can probably make 220wtq at 3000rpm on a stock motor if you want to."
Because as I have thought about it more, there are few times, if any, where torque at such a low RPM has value. Even at the drag strip, I would plan to launch at higher RPM; and on the street, I cannot hook that much torque in first gear, and all other gears are then above 4-5 K if running up through them.
And in first gear, there is not enough time or load to spool the turbo before the engine is well past 3K.
Because as I have thought about it more, there are few times, if any, where torque at such a low RPM has value. Even at the drag strip, I would plan to launch at higher RPM; and on the street, I cannot hook that much torque in first gear, and all other gears are then above 4-5 K if running up through them.
And in first gear, there is not enough time or load to spool the turbo before the engine is well past 3K.
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12-06-2018, 08:14 PM
#45
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A thought experiment:
Take a 3 foot long steel roundbar, 1/2" in diameter.
You stand it on its end and apply increasing mass to the top of the steel rod until you find the force required to fold the rod onto itself.
If you watched the rod fold on high speed you would see that the rod is being initially bent through its elastic deformation stage and quite a few milliseconds would pass before the rod reaches its plastic deformation stage.
Therefor if the load is applied for a lesser period of time than it takes to reach plastic deformation the rod will not permanently deform.
Assuming 8,000 rpm in a 4 stroke, and 20 crankshaft degrees of peak cylinder pressure the load is applied for less than 1 millisecond.
What do you all think? I have run this past a mechanical engineering phd (a friend) and a physics phd (my auntie) who agree.
Dann
Take a 3 foot long steel roundbar, 1/2" in diameter.
You stand it on its end and apply increasing mass to the top of the steel rod until you find the force required to fold the rod onto itself.
If you watched the rod fold on high speed you would see that the rod is being initially bent through its elastic deformation stage and quite a few milliseconds would pass before the rod reaches its plastic deformation stage.
Therefor if the load is applied for a lesser period of time than it takes to reach plastic deformation the rod will not permanently deform.
Assuming 8,000 rpm in a 4 stroke, and 20 crankshaft degrees of peak cylinder pressure the load is applied for less than 1 millisecond.
What do you all think? I have run this past a mechanical engineering phd (a friend) and a physics phd (my auntie) who agree.
Dann
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12-06-2018, 08:19 PM
#46
Tweaking Enginerd
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The best clause I have seen in this is from Savington... "if you want to".. in this statement: "Keep the timing soft and you can probably make 220wtq at 3000rpm on a stock motor if you want to."
Because as I have thought about it more, there are few times, if any, where torque at such a low RPM has value. Even at the drag strip, I would plan to launch at higher RPM; and on the street, I cannot hook that much torque in first gear, and all other gears are then above 4-5 K if running up through them.
And in first gear, there is not enough time or load to spool the turbo before the engine is well past 3K.
Because as I have thought about it more, there are few times, if any, where torque at such a low RPM has value. Even at the drag strip, I would plan to launch at higher RPM; and on the street, I cannot hook that much torque in first gear, and all other gears are then above 4-5 K if running up through them.
And in first gear, there is not enough time or load to spool the turbo before the engine is well past 3K.
Power everywhere, regardless of gear or rpm, is pretty nice on the street.
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12-07-2018, 12:43 AM
#51
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12-07-2018, 01:33 AM
#53
Creep describes plastic deformation below yield stress as a function of time. So the more general question of "what stress will this part meaningfully deform at" can include time as a variable, even if it's not strictly called the yield stress. But I agree that this is not relevant to this discussion, since a con rod run at 3000rpm for 1 minute and a con rod run at 7000rpm for 1 minute spend the exact same amount of time in compression.
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12-07-2018, 01:38 AM
#54
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FWIW, I ran 240-ish rwhp (dynojet) for 50K+ miles on a totally stock 99 motor, and when I took it apart to build it (because I wanted to make more), the rods were straight as an arrow. That motor never ran boost with less than 95 octane though.
--Ian
--Ian
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