Useless Spoolup Info

[Scoobum]

For those that are too lazy to look it up.

Want your engine to spool/rev up quicker...then here ya' go:

RJC billet aluminum pulleys...and if you can only afford one...get the crank pulley.
9.5" torque convertor...th ink of the weight savings over the stock 12" D5
Balanced rotating assembly
Aluminum driveshaft
Aluminum rear drums
Billet rims...the ones on my car weigh 9 lbs each...compare d to the GN steel rims weighing 28
Erics TT chip...allows you to pull low gear/spoolup fuel and add low gear timing and aggressive mode with his alky chip.

Removing 1 pound of rotating mass is the equivalent of removing 7 pounds of static weight.

[earlbrown]

Removing 1 pound of rotating mass is the equivalent of removing 7 pounds of static weight.

I cringe every time I see overly simplistic (and wrong) statements like that.

[Scoobum]

I did say it was useless info.

[TexasT]

Hey, cool guy wheels are needed. Just look at those giant rims on them donk and slab cars. Surely they help the car go faster.

[good2win22]

Removing 1 pound of rotating mass is the equivalent of removing 7 pounds of static weight.

Maybe it's the dork in me but I sure would like to see exactly how this statement came to fruition... and the formula used to derive this answer

[TexasT]

It was in a magazine once and spiraled out of control. Or maybe not.

[good2win22]

The dork took over and found this on a BMW site:
Conventional wisdom says that conservatively, 1lb worth of rotating mass lost is roughly equivalent to a 4lb sprung mass lost.  This being said, I don't think there's any way to get an exact measurement.  Even where the rotating mass is lost will make a difference.  1lb lost at the tire tread will make a bigger difference than 1 lb lost near wheel bolts.

In terms of converting that to horsepower, it depends on the power to weight ratio before the weight loss.

For instance, let's just assume we agree with the 4/1 ratio for rotating vs spring.

Let's further assume we're talking about a 4000lb vehicle with 500hp (ie.  much like an E60 M5).  We're starting off with a 8 lbs per hp ratio.

Let's take 50 lbs off of the rotating mass.  Given our 4/1 assumption above, that is equivalent to losing 200 lbs.  We're now at 3800lbs and 500hp, giving us 7.6 lbs per hp.

If we wanted to do this by increasing horsepower instead of losing weight:

4000 / 7.6 = 526hp

In other words, we could gain 26hp and we'd be at the "same place."

How much weight would we need to lose to be equal to a 100hp gain in this example?

4000 / 600 = 6.67 lbs per hp

6.67 * 500 = 3333.3 lbs

4000 - 3333.3 = 666.67 lbs sprung weight lost

666.67 / 4 = 166.67 lbs rotating weight lost

166.67 lbs is a LOT of rotating weight to lose
 

[motorhead]

I trust virtually nothing I read on model-specific enthusiast boards - because hillbilly physics.

You'll find more about the effects of rotational mass here: https://www.google.ca/search?q=moment+of+inertia+speedtalk+rotational+mass&oq=moment+of+inertia+speedtalk+rotational+mass&gs_l=mobile-heirloom-serp.3...14302.18916.0.19403.16.16.0.0.0.0.373.3242.2j6j7j1.16.0.msedr...0...1c.1.34.mobile-heirloom-serp..12.4.759.y7jJZz-wmv4&gws_rd=ssl#q=moment+of+inertia+speedtalk+rotational+mass+site:speedtalk.com&safe=off

And yes, the better the N/A engine you build the better it responds to boost.

[earlbrown]

I like how losing weight at the wheels is any kind of equivalent of sprung weight...


Last time I checked, wheels are unstrung weight.


it's all about polar moment of inertia.    It's the distance from the centerline that is just so slight a factor.


Try this, grab a 15# bowling ball and hold it against your chest.  Clock out long it takes to spin your body to full speed.  Then clock how long it takes to stop. 



Then hold the same ball at arms length and do the spin test again.   After your arm bones fuse back together, write down the difference an arms length made.

Fun fact. The weight exerted on the floor was the same on both tests.

[Steve Wood]

It's really a complex calculation and there are a lot of variables at play.

For instance reducing weight of the pulleys, flex plate, converter has a greater effect in first gear than it does in second gear and even more so when compared to third because we are dealing with rotational acceleration which is affect by the gear ratios.

Reducing weight of the wheel/tires gives a variable result because, as Earl points out, the effect depends upon where along the radius the weight was removed.

Removing weight  is good.  Reducing rotational weight is also good...but how good may not be nearly as good as one thinks.

I was thinking the other day that I have been playing with cars about 55 years.  And, if you take any ten year period, about 95% of what I learned turns out to be untrue at some later date.  Magazines are always interesting but they tend to print what their advertisers want them to print.  Often the results cited have zero to do with the reasons written down.

There is a reason that the really successful guys employ top notch engineers and there is a reason why they seldom tell us the real truth behind why they do what they do.  In the day of Google, science is taking a real hit.

[TexasT]

When does light become too light? I know when doing work torque is what gets it done. A big flywheel to keep ot spinning helps in many applications. That in motion and at rest statement and all.

[good2win22]

HRE wheels president explains rotational inertia:
 
https://youtu.be/-3FDthcLieE

[earlbrown]

When does light become too light? I know when doing work torque is what gets it done. A big flywheel to keep ot spinning helps in many applications. That in motion and at rest statement and all.

Mot really. A flywheels takes away from the power pulse and stores it.  It also acts as a smoothing medium of sorts between power pulses.  I.E. conveterting kinetic energy into potential energy and  back....

They also pay attention to moments of inertia, hence the large O.D.    The same way a smaller torque converter allows an engine to rev faster.

[motorhead]

https://www.physicsforums.com/threads/rotational-mass-and-energy-required.577882/

Simple calculators: http://hpwizard.com/rotational-inertia.html

[Scoobum]

When does light become too light? I know when doing work torque is what gets it done. A big flywheel to keep ot spinning helps in many applications. That in motion and at rest statement and all.

Maybe you could stop by my local track and explain the big flywheel thing to the guy with the 4 speed 55 Chev that falls on its face when launched.

All this weight talk reminds me. I gotta drop off this fiberglass bumper at the bodyshop and get 'er painted.

Let's keep this thread rolling. True or false. Higher compression ratio produces more exhaust velocity and more heat...thus quickening spool time.