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post #1 of (permalink) Old 12-11-2002, 05:34 PM Thread Starter
 
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more rotating mass= more torque, right?

My buddy and i got to talking about torque, he says that more rotating mass= less torque because it hinders revs. Im saying the heavier crank and flywheel will make a gain in torque. Im told him that revs will gain more horspower, but not torque. who is right?
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post #2 of (permalink) Old 12-11-2002, 06:57 PM
 
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Re: more rotating mass= more torque, right?

my thought is look at the crank on a 454 vs a 305. A 454 has more rotating mass and more torque. how high the motor revs rreally has nothing to do with it
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post #3 of (permalink) Old 12-11-2002, 07:11 PM Thread Starter
 
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Re: more rotating mass= more torque, right?

i used this analagy, a 396 big block vs a 400 smallblock, basically the same displacement and stroke. But the 396 makes more torque, even though its a margianal amount because of the heavier crank.
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post #4 of (permalink) Old 12-11-2002, 07:36 PM
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Re: more rotating mass= more torque, right?

the way i understand torque is "how hard is it to stop the motor". translated litterly from another language it would be "rotational momentum", the higher the mass, the higher the momentum at the same rpm. diesels make a crap load of torque, but they will never rev as high as a gas motor, so you would be correct on all points. but also weight is not the only way to get touque.
post #5 of (permalink) Old 12-11-2002, 11:48 PM
 
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Re: more rotating mass= more torque, right?

it all depends on how you're looking at it and what the system constraints are. basically torque is a "moment of inertia" from a static standpoint it is defined as " a force applied at a distance" like whn you're trying to loosen a stuck bolt. would you use the 10" rachet, or add a 36" cheater bar to it? add the extra distance and the torque is multiplied. so basically it works the same for rotation masses. given the same sized wheels. it takes more torque to spin a solid rubber wheel versus a pneumatic wheel. since it has less mass. this isa good example becasue the bulk of the mass is near the outer portion.
torque in an engine depends on a lot of things...compression stroke, bore...etc etc. but if two engines were identical and the rotating mass (crank and flywheel) were oif different masses. it would be easier to stall out the engine with the lesser rotating mass.
I"m not sure what it would be like in a real application thouhg. becasue it takes more energy to get the mass moving faster in the high mass engine. i gues it depends on how you look at it.
hmmm, ididnt answer the question really, but perhaps shed some light on the issue. this same issue ois why a brake upgrade is important when upgrading to larger tires. ti takes more power to stop the rotational mass of the bigger tires along with the increase in regular old mass.
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post #6 of (permalink) Old 12-12-2002, 12:07 AM
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Re: more rotating mass= more torque, right?

Torque is the amount of "twist" applied to the tranny, bolt,
or whatever.
It has nothing to do with mass.

Take for example a torque wrench.
Pull 50 lbs on it at 1 foot = 50 ft/lbs.
Pull 25 lbs on it at 2 feet, - same = 50 ft lbs.
Pull 100 lbs on it at 6", same = 50 ft/lbs.

The bolt ended up with the same amount of tightness.
The differences was only leverage.

The weight of the wrench (flywheel) - inertial mass - never
came into play, whether the wrench weighed 1 lb or 100 lbs.
And the speed at which you pulled it never came into play
either, whether you jerked it or did it slowly, 50 ft/lbs
is 50 ft/lbs.

The heavier flywheel inhibits rate of change of engine RPM,
whether speeding up or slowing down, but does not change
torque.
Think about it - does removing a flywheel and installing a
flex plate affect the ability of the engine to generate
torque?

Horsepower is a theoretical measurment, calculation, using
torque and speed.
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post #7 of (permalink) Old 12-12-2002, 05:19 AM
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Re: more rotating mass= more torque, right?

There are several things that come into play with a bigblock vs. smallblock debate. There's a reason you'll rarely ever find a smallblock in a farm truck.

Low RPM volumetric efficiency is important. You also need to look at bore vs. stroke. A very important thing is deck height.
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post #8 of (permalink) Old 12-12-2002, 07:57 AM
 
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Re: more rotating mass= more torque, right?

I'm an engine expert by no means, but i believe that it is the throw of the crank that creates most of your torque. The larger throw increases mechanical advantage of the pistion on the crank centerline. Isn't this why people make 383's, to produce more torque using a crank with a longer throw?

Anyway, i think that it is engine geometery, not mass, that produces torque.
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post #9 of (permalink) Old 12-12-2002, 08:15 AM
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Re: more rotating mass= more torque, right?

for more torque DEISEL is what i have heard. but that is expensive and i am in college, and have no money... so plan B.

i think that the more mass on the crank itself means that there will be slower throttle response time. Big blocks have tons o power. What i am thinkin of eventually doin on the K5 is putting in a 383 stroker. I hear those bad boys have a lot of torque. right now, with a 350 v8 and a sm465, my rear driveshaft yoke snapped from the torque that the tranny has on it. So, i think that to get more torque get better gears. Samuri guys with 44's and the I4???? yeah they have like 6.56 gears or so.
post #10 of (permalink) Old 12-12-2002, 08:40 AM
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Re: more rotating mass= more torque, right?

Well from what I have been told by every engine rebuilder I have been talking with lately, more rotating mass is bad for horsepower, and street. I have a 427 tall deck engine that I had hoped on putting into my jimmy. With the tall deck the rotating assembly is much heavier than a standard 427 light truck and car engine (its out of a 5 ton and has 4 ring pistons). The block it self is 'taller' if I remember what the guy told me. Torque wise they were monsters but they lack the ability to rev high, no horsepower, 320 - 340 horses. Every custom shop I called told me no don't do it. Find a 454 instead, or stroke the old 350. So heavier is not necessarily better.
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