Rotational Mass - All Stock vs. All Super-Light

[Brad-ManQ45]

There are a lot of drag cars that have very small high winding engines in heavy cars (class racing) that utilize a heavy flywheel to get the right amount of torque transferred to the wheels off the line. The use of a light flywheel is actually a detriment to these cars. (I'm talking like a 283 in a mid 60's Impala or something bigger, running 4.88 pr higher gears, that spin up to 9 or 10k here.

 

Light cars with big engines definitely don't need a heavy flywheel, though a heavier flywheel will make the car more tractable on the street (think throttle like an on/off switch for a light flywheel and much smoother transitions with heavier wheels.....).

 

For a pure drag car with whatever engine in one of our Z's - go LIGHT!

[Guest Mike]

Brad-ManQ45... Everything in your post makes sense to me. Any info on effects of super-light driveshafts or lightweight cranks/pistons?

[badjuju]

for #3 there are more pressing performance advantages than weight, remember that.

[Guest Mike]

badjuju... Understood. It's not really the weight though. It's how much effect excess weight has on reciprocating and revolving masses. Adding a 100 pounds of seats and doo-dads to your car's interior is noticible but not nearly as much as if you add that much weight to your crankshaft counterbalances (only weight considered/not balance issues). The engine simply will not react as quickly:burnout:

[savageskaterkid]

Tell me if I'm wrong on this, but this is what I was always told. For a rule of thumb, every 100 pounds you take off the car, will drop a tenth in the quarter. But for every 10 pounds you take off the rotational parts of the driveline, it will drop a tenth.

[dr_hunt]

Tell me if I'm wrong on this, but this is what I was always told. For a rule of thumb, every 100 pounds you take off the car, will drop a tenth in the quarter. But for every 10 pounds you take off the rotational parts of the driveline, it will drop a tenth.

 

Ten pounds off rotational, you talking engine, or drivetrain? Engine I'm assuming since it's what accelerates the fastest.

 

You all know that nothing is as insane as WOO sprint cars for light weight, aluminum rears, aluminum spools, lightened gears, carbon fiber driveshafts, direct drive clutch, no trans, coupler to the direct drive box, super light cranks, rods and pistons and if it ain't made of titanium or unobtanium your in the back of the pack. And yes, there are titanium connecting rods.

 

Probably correct, but there's a point where light weight and durability cross.

[Tony D]

check out velasco crankshafts. they have three treatments for crankshaft counterweights to increase revability. you can cut them down and lighten them more if the pistons and rods are lighter to begin with...

 

But chamfering the leading edges of the crank counterweights is very common in any serious race engine...it would be considered a "mild" application of lightening, Velasco does much more on the top-speed car crank prep. They have photos on their website I think... or maybe it was a writeup in PRI. My mind is fooked recently remembering things in print versus online... Sorry.

[Guest Mike]

"...there's a point where light weight and durability cross".

 

Yes... but where is that point, Doc? Given a particular application, where are those magic numbers? Realizing the elusiveness of these figures due to effectively infinit variables, I propose a chart with parts listed for the most popular engines and for differing HP/torque/application builds with options listed for cost compromises. Of course a "complete" list with "every" parts manufacturer listed is essentially impossible or at least economically unfeasible. A basic list is fine. People can then ask for advice regarding substitutions.

 

And before anyone says I should do this... I think most of you know how inept I am as a mechanic:wink:

[Guest Mike]

Tony D... I just performed a "Giggle" search for "velasco crankshafts" and found references to them but not their website. Can you post or PM that?

[jap tin]

It all helps. Aluminum and titanium are your friends.I have an aluminum drive shaft, aluminum spool, cut back ring gear, aluminum pinion yoke, rifle drilled axels with titanium drive studs and aluminum lug nuts. Make everthing that you turn over light as you can.

[Guest Mike]

Okay (I searched) what are "rifle drilled axles"? Axles with holes drilled in them? Any pics available?

[JMortensen]

Try google. It's an axle that looks like a gun barrel. I don't know why the call them "rifled" since there certainly aren't grooves in the axle. You actually don't need all that axle metal in the center. Its the outside portion of the metal that does most of the twisting. Just like sway bars, you can get away with using tubular axles if you make them strong enough and they have a thick enough wall.

[johnc]

In July 2005 the top F1 engine development guy at Cosworth (Nick Hayes) left and joined Richard Childress Racing and is charge of the engine R&D program. One of the problems RCR was facing was broken valves. Their original solution was to make the heavier and stronger. They still broke. Nich Hayes made them lighter and more flexible. No more breakage and a little more power.

 

Lighter engine components often contribute to increases in reliability and power. On the 3L L6 engine that Sunbelt built for me they took 15 lbs out of the crank alone and the engine worked very well.

[Turbo280Z]

yea on my 300zx i put some 350z 17"s and u can feel the diff in the weight of the wheels. u get less accell but a lil more top end IMO

[JMortensen]

yea on my 300zx i put some 350z 17"s and u can feel the diff in the weight of the wheels. u get less accell but a lil more top end IMO

I think you're confusing two things. One is the tire DIAMETER, the other is the combined tire and wheel WEIGHT. I don't know but I would guess that your new wheels are a larger diameter than the old ones. Can't speak to the weight. If the diameter is larger, then it is essentially the same as putting a taller rear gear in. You'll have a lower actual top speed, a higher theoretical top speed, and less power all the way around.

[boodlefoof]

I've always heard the axles you are referring to called "gun drilled."

[Shuyun]

The rule of thumb I have here form Engine/Car builders at Hillard Racing was 1lb or rotating mass was worth 7lb of dead weight. Rotating mass includes anything anywhere on the car that rotates wheels, axels, drive shafts, hubs, gears, cranks, fly wheel, cams, and more.

[xxjoeyxxeb]

Hey guys,

I have just taken Statics and currently in dynamics for mechanical engineering and I can say that many rotating objects are described by Force*Distance, which is a moment. The smaller distance means a smaller moment, which can explain some of the wheel sizing. Weight and angular velocities, and so many other things can affect all the variables you've been talking about. But main concepts are smaller radius and less weight do require less torque to have the same force.

[Guest Mike]

So in theory, if an object weighing a hundred million pounds (yes I know this is relative) and was infinitly small and attached with zero error in the center of a second object weighing only one ounce, this hundred million pound mass would have no effect on rotational velocity of the other object. Okay... got it:wink:

 

Is it fair to assume that the consensus regarding which components have the most effect on power/torque (in order of diminishing effect) is as follows?

 

1. Flywheel

2. Torque converter "or" clutch assembly

3. Wheels/tires

4. Pistons

5. Crank shaft (mostly counter weights)

6. Rods

7. Drive shaft

8. Half shafts

[xxjoeyxxeb]

HAHA, in theory...

Moment = Force x Distance

thats the basic equation and easiest to solve. (trust me I took Statics twice)

But in Dynamics we have done some simple automotive applications, but nothing too in depth. But I do know that the radius of things do affect rotational velocity and moments and forces needed to move them after overcoming friction.... so all these tie into play.

 

Gotta go do my Dynamics homework now... I will be doing a project on a couple automotive applications as I can relate to Dynamics due next Friday so hopefully I can do something that'll help us figure some numbers out, but I don't think we've been taught the skills for some of the in depth topics we're discussing.