Exactly this. My bumbling in trying to explain this in a linear fashion not so good.

 

I have to agree with Polyalphaolefin on this one.
Although you lose the energy stored in the heavy crankshaft it's only on the initial clutch or torque converter engagement, Anything other than that a lighter rotating assembly is free power. You're talking the first couple feet, In a roll race situation the where stored energy is not used the lighter rotating assembly will make the car accelerate faster because the energy that was being used to spin a heavy rotating assembly is now being used to propel the car forward instead. It's also the reason lightened 2 speed transmission is going to be faster than a 4-speed. Anytime you can reduce a rotational mass it will accelerate faster.
When I raced micro sprint ( 600cc R6 motorcycle engine) We removed all but two gears in the transmission = -3lbs, Removed most of the mass of the flywheel = -2lbs and used the lightest gears/ Gun drilled axles/ Lightest wheels we could find to free up power. You wouldn't think it would make that much of a difference but when the engine makes about 60-70 ftlbs of torque and about 130hp removing about 10lbs of rotating weight was a huge advantage. We turned the engine to just over 16,000 rpms. Think about how much power it takes to spin a 5lb mass from 7,000 to 16,000 rpms 40 times during a race and that's just the engine rotating weight alone. The other 5 or so pounds of rotating weight was in the rest of the driveline.
I just came home from a 410ci sprint car race, They spend ridiculous amounts of money cutting every last ounce of rotating weight even if it mean they have to add weight to the car somewhere else to make sure it's above legal minimum weight when they cross the scales.
There's an old saying "Reducing rotating weight by 10lbs is like removing 100lbs from the car" Whiles it's not quite that drastic, It is basically free power as long as you don't compromise the driveline itself and that brings to mind another old saying. " To finish first you must first finish"

 

^^^The statement above is basically true for brake drums, wheels and tires. I had the 15×7 stock alloy wheels on my 1999 Tahoe with a 30.5" tall tire that was 235 wide. I swapped to 20x9.5" wheels with a 285 wide 30.5" tall tire. I noticed a substantial difference in the unsprung/rotating mass. When I needed tires I put 32" tall P305/50R20s on it. Those were heavier yet again and the overall gear ratio reduced. Basically turned my 3.42s into 3.08s with the taller tires. At that point it felt like I was hauling around another 1,000 lbs.

 

I see this all the time in the Tahoe and Silverado groups. Guys will complain that they're only getting 10 mpg, but will have wheels and tires double the weight of stock and 4-8" lift that has the truck catching more air. On top of that, they'll have a couple hundred pounds of subs, box(es), wiring, and 2nd alternator. Yet they wonder why their gas mileage sucks.

 

Funny you say that. That same truck still has the same wheels and tires, has a 2" body lift but has an 8.1/6spd allison in it. It also has a sub box and a pair of 145a AD-244 alternators. Gets about the same mileage now that it did with the stock 350 and cammed 305. It cruises under 2,000 rpm @ 85 mph and the marine HO cammed 8.1 has plenty of torque.

 

This guy, listen to this guy ^^^^^

I've done the lightweight rotating assembly thing. Its AMAZING if you have an automatic. Its TEDIOUS if you have a manual.
In both cases it will save fuel and free up power.

 

Do you have documentation to support this?


Another thing to consider, how does this assembly affect manual driving in winter? In order to get my car moving in relatively deep snow and even with ice underneath, I need to have very precise control with lots of clutch riding to spin my tires slow enough so as I don't dig a hole and get the car stuck. This is where wide tires help in an unexpected way versus pizza-cutters. How exactly would a lighter assembly behave if I need to speed the engine a bit more faster than I otherwise would with the heavier stock assembly? Then, to make matters worse, when driving I need to shift smooth so as not to start fishtailing. If the lighter assembly drops RPMs too quickly this could cause another serious problem.

SS RRR, the build I have in mind is done with year-round daily driving in mind and including hard winter driving. Fuel economy has to be a focus but also the manners of the engine and how much torque it can throw down off idle. With all of this said, thank you for your input as I start to see more and more that going lighter for my daily driving will be a mistake.

 

I have a feeling you'll never get the exact answer that you're looking for because you keep circling yourself on what answer you seek. Just put a simple kit together and send it. You, the driver, have more input on any of these variables than a 50-100 gram difference in bobweight.

I'm all for talking theory and physics. It's what I do everyday. There's a limit of practicality though.

 

A good set of snow tires.

 

lol @ documentation, its called experience

Documents that show what? How tedious it is to drive a manual trans with no weight in the rotating parts?
Just imagine how fast the engine would stop if it was weightless.

ex. Spin a weightless object in zero gravity and grab it with your hand. What happens? It stops instantly.
ex2. spin a very very heavy object in zero gravity and grab it with your hand. What happens? It rips your hand off.
ex3. take a 300kg wheel to the track, spin it up to about 500rpm and then drop it on the track, what happens? It will go quite a distance before running out of energy
ex4. take a 0.01lb wheel to the track, spin it up to about 500rpm and then drop it on the track. What happens? It will stop and fall over instantly.

What you are looking at is the difference in energy stored inside a rotating part. The heavier the part, more energy is stored.
The stored energy is what keeps it spinning. If the flywheel as 3000lbs and the vehicle was 1lb, the vehicle could not slow down the flywheel when you let out the clutch.
Likewise if the flywheel is 1lb and the vehicle is 3000lbs, the flywheel will stop instantly if you let out the clutch (engine stall)

these extreme examples should make it obvious that having a very light "flywheel" (everything connected to the flywheel counts as flywheel weight more or less)
is not a good idea in a daily. You are at a light and not paying attention you will stall the engine. You shift a gear and the rpm drops so fast you mess the natural synchronization event if you aren't in 100% racing shift mode. You put it into first and try to get the car moving uphill but the flywheel is so light you have to rev the engine really high and wind up torching the clutch trying to feather it. You are in stop and go traffic and every 5 seconds you have to rev the engine to the moon to move 3 feet,
It could melt/ruin the clutch or cause hate driving the car.

documentation be damned

 

Oh dear....

 

there are (perhaps hundreds) of models on the internet:
https://www.mathworks.com/videos/mod...ain-68822.html
If you sit down with paper to create a model of something simple it can be dramatic:


To actually "do" anything rapidly enough you will want to simulate a model using a computer, and adjust variables over time under various conditions.
In a controls course we created equation like above and used it to simulate several different electrical motors, then measured their frequency response and other details while adjusting it to be more comparable to a real electric motor we also had to measure from. The simulation can come very close to the real thing and then by examining phase and amplitude (Bode plot will show peak resonance and other behaviors) it becomes possible to dampen or accentuate the response of a dynamical system, by controlling it to fall within that range. For example my professor had an electric jellyfish and there was a peak resonance at some specific operating frequency, so they programmed a micocontroller to keep it operating in that range to take advantage of the additional energy that was available to move the robot. They were only able to find that peak area because of the simulation model though. For example if you design a whole car without these models it will have all kinds of vibration issues to deal with, and not just in the engine/drivetrain, there are resonances in any dynamic system such as exhaust/intake gas flow which is how engineers choose runner length in intake manifolds and header length for racing at specific operating frequencies (rpm) without empirical testing (but it still usually requires testing and re-evaluation, its just the first test is much closer to 'finished' hopefully)

Engines are remarkably simple compared to most other machines I've glimpsed. Even if knowing everything about engines seems like it will be insignificant and practically useless in the vast majority of other machine encounters. Even an airplane seems basic, I would switch to them because its just a light car with wings.

 

If we're going to get really technical, all objects in zero gravity would be weightless.

 

they will still collect and contain kinetic rotating energy which can easily rip your hands off if you touch it while its spinning
If you take a huge fan to outer space and let it go floating around, then from your space ship power it up and spin it very fast,
anything that touches it will be subject to the rotating kinetic energy and get torn apart if the fan materials can sustain the forces.

 

Why must you insist in doing this crap? You always have a 3,000 word response that in the end people don't bother to read because it's a bunch on crap that has little to do with the topic. Nobody is in outer space but you apparently.
I really wish you took the reason for the last ban seriously.

 

Understood, and that’s a function of their mass, which is constant. Sorry. I was a physics major until my brain could no longer keep up.

 

So uhm. What was your intended message/correction? lol

Sorry now I'm the one whos confused, oh was it because I said pounds as in Earth gravity?
I understand your adherence to units /unit systems and mentioning it online is acceptable when there is a correction that alters the meaning of the entire passage, I agree.

In this case I thought it was clear that the object weight is 3000lbs here on Earth first, then we shot it into space and did the kinetic energy tests.

However your point remains valid, I rarely consider zero gravity situations so it isn't automatic for me to convert to mass. But you are right, I really should have used mass measurements when switching to 0g.

 

Why not think of your largest problem in life, and PM it to me,

and I will try to fix it because I am bored for 50 more hours.

Because I love all life, especially humans but I save ants too if I can.

 

The key is to inject a crap ton, IE no jets at all, of nitrous to power through that light weight stuff and ******* send it.

Every red light. SEND IT.

 

Was thinking about putting this on my LP. Is my car too slow to deserve such a legendary phrase?